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impala/docs/topics/impala_math_functions.xml
Anshula Jain ca3fe6d6af IMPALA-12692 : [DOCS] Typo in docs about random() function 
Changed name of random fucntion in impala_math_functions.xml
from "RANDOME(), RANDOME(BIGINT seed)" to "RANDOM(), RANDOM(BIGINT seed)"

Change-Id: I4844eb8d155326081c385d88b98a591dbbde7369
Reviewed-on: http://gerrit.cloudera.org:8080/21126
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
Reviewed-by: Michael Smith <michael.smith@cloudera.com>
2024-03-08 16:34:50 +00:00

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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="math_functions">
<title>Impala Mathematical Functions</title>
<titlealts audience="PDF">
<navtitle>Mathematical Functions</navtitle>
</titlealts>
<prolog>
<metadata>
<data name="Category" value="Impala"/>
<data name="Category" value="Impala Functions"/>
<data name="Category" value="SQL"/>
<data name="Category" value="Data Analysts"/>
<data name="Category" value="Developers"/>
<data name="Category" value="Querying"/>
</metadata>
</prolog>
<conbody>
<p>
Mathematical functions, or arithmetic functions, perform numeric calculations that are
typically more complex than basic addition, subtraction, multiplication, and division. For
example, these functions include trigonometric, logarithmic, and base conversion
operations.
</p>
<note>
In Impala, exponentiation uses the <codeph>pow()</codeph> function rather than an
exponentiation operator such as <codeph>**</codeph>.
</note>
<p conref="../shared/impala_common.xml#common/related_info"/>
<p>
The mathematical functions operate mainly on these data types:
<xref href="impala_int.xml#int"/>, <xref href="impala_bigint.xml#bigint"/>,
<xref href="impala_smallint.xml#smallint"/>, <xref href="impala_tinyint.xml#tinyint"/>,
<xref href="impala_double.xml#double"/>, <xref href="impala_float.xml#float"/>, and
<xref href="impala_decimal.xml#decimal"/>. For the operators that perform the standard
operations such as addition, subtraction, multiplication, and division, see
<xref href="impala_operators.xml#arithmetic_operators"/>.
</p>
<p>
Functions that perform bitwise operations are explained in
<xref href="impala_bit_functions.xml#bit_functions"/>.
</p>
<p>
<b>Function reference:</b>
</p>
<p>
Impala supports the following mathematical functions:
</p>
<ul>
<li>
<xref href="#math_functions/abs">ABS</xref>
</li>
<li>
<xref href="#math_functions/acos">ACOS</xref>
</li>
<li>
<xref href="#math_functions/asin">ASIN</xref>
</li>
<li>
<xref href="#math_functions/atan">ATAN</xref>
</li>
<li>
<xref href="#math_functions/atan2">ATAN2</xref>
</li>
<li>
<xref href="#math_functions/bin">BIN</xref>
</li>
<li>
<xref href="#math_functions/ceil">CEIL, CEILING, DCEIL</xref>
</li>
<li>
<xref href="#math_functions/conv">CONV</xref>
</li>
<li>
<xref href="#math_functions/cos">COS</xref>
</li>
<li>
<xref href="#math_functions/cosh">COSH</xref>
</li>
<li>
<xref href="#math_functions/cot">COT</xref>
</li>
<li>
<xref href="#math_functions/degrees">DEGREES</xref>
</li>
<li>
<xref href="#math_functions/e">E</xref>
</li>
<li>
<xref href="#math_functions/exp">EXP</xref>
</li>
<li>
<xref href="#math_functions/factorial">FACTORIAL</xref>
</li>
<li>
<xref href="#math_functions/floor">FLOOR, DFLOOR</xref>
</li>
<li>
<xref href="#math_functions/fmod">FMOD</xref>
</li>
<li>
<xref href="#math_functions/fnv_hash">FNV_HASH</xref>
</li>
<li>
<xref href="#math_functions/greatest">GREATEST</xref>
</li>
<li>
<xref href="#math_functions/hex">HEX</xref>
</li>
<li>
<xref href="#math_functions/is_inf">IS_INF</xref>
</li>
<li>
<xref href="#math_functions/is_nan">IS_NAN</xref>
</li>
<li>
<xref href="#math_functions/least">LEAST</xref>
</li>
<li>
<xref href="#math_functions/ln">LN</xref>
</li>
<li>
<xref href="#math_functions/log">LOG</xref>
</li>
<li>
<xref href="#math_functions/log10">LOG10</xref>
</li>
<li>
<xref href="#math_functions/log2">LOG2</xref>
</li>
<li>
<xref href="#math_functions/max_int">MAX_INT, MAX_TINYINT, MAX_SMALLINT,
MAX_BIGINT</xref>
</li>
<li>
<xref href="#math_functions/min_int">MIN_INT, MIN_TINYINT, MIN_SMALLINT,
MIN_BIGINT</xref>
</li>
<li>
<xref href="#math_functions/mod">MOD</xref>
</li>
<li>
<xref href="#math_functions/murmur_hash">MURMUR_HASH</xref>
</li>
<li>
<xref href="#math_functions/negative">NEGATIVE</xref>
</li>
<li>
<xref href="#math_functions/pi">PI</xref>
</li>
<li>
<xref href="#math_functions/pmod">PMOD</xref>
</li>
<li>
<xref href="#math_functions/positive">POSITIVE</xref>
</li>
<li>
<xref href="#math_functions/pow">POW, POWER, DPOW, FPOW</xref>
</li>
<li>
<xref href="#math_functions/precision">PRECISION</xref>
</li>
<li>
<xref href="#math_functions/quotient">QUOTIENT</xref>
</li>
<li>
<xref href="#math_functions/radians">RADIANS</xref>
</li>
<li>
<xref href="#math_functions/rand">RAND, RANDOM</xref>
</li>
<li>
<xref href="#math_functions/round">ROUND, DROUND</xref>
</li>
<li>
<xref href="#math_functions/scale">SCALE</xref>
</li>
<li>
<xref href="#math_functions/sign">SIGN</xref>
</li>
<li>
<xref href="#math_functions/sin">SIN</xref>
</li>
<li>
<xref href="#math_functions/sinh">SINH</xref>
</li>
<li>
<xref href="#math_functions/sqrt">SQRT</xref>
</li>
<li>
<xref href="#math_functions/tan">TAN</xref>
</li>
<li>
<xref href="#math_functions/tanh">TANH</xref>
</li>
<li>
<xref href="#math_functions/truncate">TRUNCATE, DTRUNC, TRUNC</xref>
</li>
<li>
<xref href="#math_functions/unhex">UNHEX</xref>
</li>
<li>
<xref href="#math_functions/width_bucket">WIDTH_BUCKET</xref>
</li>
</ul>
<dl>
<dlentry rev="1.4.0" id="abs">
<dt rev="1.4.0 2.0.1">
ABS(numeric_type a)
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Returns the absolute value of the argument.
<p
rev="2.0.1"
conref="../shared/impala_common.xml#common/return_type_same"/>
<p>
<b>Usage notes:</b> Use this function to ensure all return values are positive. This
is different than the <codeph>POSITIVE()</codeph> function, which returns its
argument unchanged (even if the argument was negative).
</p>
</dd>
</dlentry>
<dlentry id="acos">
<dt>
ACOS(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the arccosine of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="asin">
<dt>
ASIN(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the arcsine of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="atan">
<dt>
ATAN(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the arctangent of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="atan2" rev="2.3.0 IMPALA-1771">
<dt rev="2.3.0 IMPALA-1771">
ATAN2(DOUBLE a, DOUBLE b)
</dt>
<dd rev="2.3.0 IMPALA-1771">
<b>Purpose:</b> Returns the arctangent of the two arguments, with the signs of the
arguments used to determine the quadrant of the result.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="bin">
<dt>
BIN(BIGINT a)
</dt>
<dd>
<b>Purpose:</b> Returns the binary representation of an integer value, that is, a
string of 0 and 1 digits.
<p>
<b>Return type:</b> <codeph>STRING</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="ceil">
<dt rev="1.4.0">
CEIL(DOUBLE a), CEIL(DECIMAL(p,s) a), CEILING(DOUBLE a), CEILING(DECIMAL(p,s) a),
DCEIL(DOUBLE a), DCEIL(DECIMAL(p,s) a)
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Returns the smallest integer that is greater than or equal to the
argument.
<p>
<b>Return type:</b> Same as the input value
</p>
</dd>
</dlentry>
<dlentry id="conv">
<dt>
CONV(BIGINT n, INT from_base, INT to_base), CONV(STRING s, INT from_base, INT to_base)
</dt>
<dd>
<b>Purpose:</b> Returns a string representation of the first argument converted from
<codeph>from_base</codeph> to <codeph>to_base</codeph>. The first argument can be
specified as a number or a string. For example, <codeph>CONV(100, 2, 10)</codeph> and
<codeph>CONV('100', 2, 10)</codeph> both return <codeph>'4'</codeph>.
<p>
<b>Return type:</b> <codeph>STRING</codeph>
</p>
<p>
<b>Usage notes:</b>
</p>
<p>
If <codeph>to_base</codeph> is negative, the first argument is treated as signed,
and otherwise, it is treated as unsigned. For example:
</p>
<ul>
<li>
<codeph>conv(-17, 10, -2) </codeph>returns <codeph>'-10001'</codeph>,<codeph>
-17</codeph> in base 2.
</li>
<li>
<codeph>conv(-17, 10, 10)</codeph> returns
<codeph>'18446744073709551599'</codeph>. <codeph>-17</codeph> is interpreted as an
unsigned, 2^64-17, and then the value is returned in base 10.
</li>
</ul>
<p>
The function returns <codeph>NULL</codeph> when the following illegal arguments are
specified:
</p>
<ul>
<li>
Any argument is <codeph>NULL</codeph>.
</li>
<li>
<codeph>from_base</codeph> or <codeph>to_base</codeph> is below
<codeph>-36</codeph> or above <codeph>36</codeph>.
</li>
<li>
<codeph>from_base</codeph> or <codeph>to_base</codeph> is <codeph>-1</codeph>,
<codeph>0</codeph>, or <codeph>1</codeph>.
</li>
<li>
The first argument represents a positive number and <codeph>from_base</codeph> is
a negative number.
</li>
</ul>
<p>
If the first argument represents a negative number and <codeph>from_base</codeph> is
a negative number, the function returns <codeph>0</codeph>.
</p>
<p>
If the first argument represents a number larger than the maximum
<codeph>bigint</codeph>, the function returns:
</p>
<ul>
<li>
The string representation of -1 in <codeph>to_base</codeph> if
<codeph>to_base</codeph> is negative.
</li>
<li>
The string representation of 18446744073709551615' (2^64 - 1) in
<codeph>to_base</codeph> if <codeph>to_base</codeph> is positive.
</li>
</ul>
<p>
If the first argument does not represent a valid number in
<codeph>from_base</codeph>, e.g. 3 in base 2 or '1a23' in base 10, the digits in the
first argument are evaluated from left-to-right and used if a valid digit in
<codeph>from_base</codeph>. The invalid digit and the digits to the right are
ignored.
</p>
<p>
For example:
<ul>
<li>
<codeph> conv(445, 5, 10)</codeph> is converted to <codeph>conv(44, 5,
10)</codeph> and returns <codeph>'24'</codeph>.
</li>
<li>
<codeph> conv('1a23', 10, 16)</codeph> is converted to <codeph>conv('1', 10 ,
16)</codeph> and returns <codeph>'1'</codeph>.
</li>
</ul>
</p>
</dd>
</dlentry>
<dlentry id="cos">
<dt>
COS(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the cosine of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="cosh" rev="2.3.0 IMPALA-1771">
<dt rev="2.3.0 IMPALA-1771">
COSH(DOUBLE a)
</dt>
<dd rev="2.3.0 IMPALA-1771">
<b>Purpose:</b> Returns the hyperbolic cosine of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="cot" rev="2.3.0 IMPALA-1771">
<dt rev="2.3.0 IMPALA-1771">
COT(DOUBLE a)
</dt>
<dd rev="2.3.0 IMPALA-1771">
<b>Purpose:</b> Returns the cotangent of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
<p conref="../shared/impala_common.xml#common/added_in_230"/>
</dd>
</dlentry>
<dlentry id="degrees">
<dt>
DEGREES(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Converts argument value from radians to degrees.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="e">
<dt>
E()
</dt>
<dd>
<b>Purpose:</b> Returns the
<xref
href="https://en.wikipedia.org/wiki/E_(mathematical_constant"
scope="external" format="html">mathematical
constant e</xref>.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="exp">
<dt>
EXP(DOUBLE a), DEXP(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the
<xref
href="https://en.wikipedia.org/wiki/E_(mathematical_constant"
scope="external" format="html">mathematical
constant e</xref> raised to the power of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="2.3.0" id="factorial">
<dt rev="2.3.0">
FACTORIAL(integer_type a)
</dt>
<dd rev="2.3.0">
<b>Purpose:</b> Computes the
<xref
href="https://en.wikipedia.org/wiki/Factorial" scope="external"
format="html">factorial</xref>
of an integer value. It works with any integer type.
<p
conref="../shared/impala_common.xml#common/added_in_230"/>
<p>
<b>Usage notes:</b> You can use either the <codeph>factorial()</codeph> function or
the <codeph>!</codeph> operator. The factorial of 0 is 1. Likewise, the
<codeph>factorial()</codeph> function returns 1 for any negative value. The maximum
positive value for the input argument is 20; a value of 21 or greater overflows the
range for a <codeph>BIGINT</codeph> and causes an error.
</p>
<p>
<b>Return type:</b> <codeph>BIGINT</codeph>
</p>
<p conref="../shared/impala_common.xml#common/added_in_230"/>
<codeblock>select factorial(5);
+--------------+
| factorial(5) |
+--------------+
| 120 |
+--------------+
select 5!;
+-----+
| 5! |
+-----+
| 120 |
+-----+
select factorial(0);
+--------------+
| factorial(0) |
+--------------+
| 1 |
+--------------+
select factorial(-100);
+-----------------+
| factorial(-100) |
+-----------------+
| 1 |
+-----------------+
</codeblock>
</dd>
</dlentry>
<dlentry id="floor">
<dt>
FLOOR(DOUBLE a), FLOOR(DECIMAL(p,s) a), DFLOOR(DOUBLE a), DFLOOR(DECIMAL(p,s) a)
</dt>
<dd>
<b>Purpose:</b> Returns the largest integer that is less than or equal to the
argument.
<p>
<b>Return type:</b> Same as the input type
</p>
</dd>
</dlentry>
<dlentry id="fmod">
<dt>
FMOD(DOUBLE a, DOUBLE b), FMOD(FLOAT a, FLOAT b)
</dt>
<dd>
<b>Purpose:</b> Returns the modulus of a floating-point number.
<p>
<b>Return type:</b> <codeph>FLOAT</codeph> or <codeph>DOUBLE</codeph>, depending on
type of arguments
</p>
<p conref="../shared/impala_common.xml#common/added_in_111"/>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p>
Because this function operates on <codeph>DOUBLE</codeph> or <codeph>FLOAT</codeph>
values, it is subject to potential rounding errors for values that cannot be
represented precisely. Prefer to use whole numbers, or values that you know can be
represented precisely by the <codeph>DOUBLE</codeph> or <codeph>FLOAT</codeph>
types.
</p>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
The following examples show equivalent operations with the <codeph>fmod()</codeph>
function and the <codeph>%</codeph> arithmetic operator, for values not subject to
any rounding error.
</p>
<codeblock>select fmod(10,3);
+-------------+
| fmod(10, 3) |
+-------------+
| 1 |
+-------------+
select fmod(5.5,2);
+--------------+
| fmod(5.5, 2) |
+--------------+
| 1.5 |
+--------------+
select 10 % 3;
+--------+
| 10 % 3 |
+--------+
| 1 |
+--------+
select 5.5 % 2;
+---------+
| 5.5 % 2 |
+---------+
| 1.5 |
+---------+
</codeblock>
<p>
The following examples show operations with the <codeph>fmod()</codeph> function for
values that cannot be represented precisely by the <codeph>DOUBLE</codeph> or
<codeph>FLOAT</codeph> types, and thus are subject to rounding error.
<codeph>fmod(9.9,3.0)</codeph> returns a value slightly different than the expected
0.9 because of rounding. <codeph>fmod(9.9,3.3)</codeph> returns a value quite
different from the expected value of 0 because of rounding error during intermediate
calculations.
</p>
<codeblock>select fmod(9.9,3.0);
+--------------------+
| fmod(9.9, 3.0) |
+--------------------+
| 0.8999996185302734 |
+--------------------+
select fmod(9.9,3.3);
+-------------------+
| fmod(9.9, 3.3) |
+-------------------+
| 3.299999713897705 |
+-------------------+
</codeblock>
</dd>
</dlentry>
<dlentry rev="1.2.2" id="fnv_hash">
<dt rev="1.2.2">
FNV_HASH(type v),
</dt>
<dd rev="1.2.2">
<b>Purpose:</b> Returns a consistent 64-bit value derived from the input argument, for
convenience of implementing hashing logic in an application.
<p>
<b>Return type:</b> <codeph>BIGINT</codeph>
</p>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p>
You might use the return value in an application where you perform load balancing,
bucketing, or some other technique to divide processing or storage.
</p>
<p>
Because the result can be any 64-bit value, to restrict the value to a particular
range, you can use an expression that includes the <codeph>ABS()</codeph> function
and the <codeph>%</codeph> (modulo) operator. For example, to produce a hash value
in the range 0-9, you could use the expression <codeph>ABS(FNV_HASH(x)) %
10</codeph>.
</p>
<p>
This function implements the same algorithm that Impala uses internally for hashing,
on systems where the CRC32 instructions are not available.
</p>
<p>
This function implements the
<xref
href="http://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function"
scope="external" format="html">Fowler–Noll–Vo
hash function</xref>, in particular the FNV-1a variation. This is not a perfect hash
function: some combinations of values could produce the same result value. It is not
suitable for cryptographic use.
</p>
<p>
Similar input values of different types could produce different hash values, for
example the same numeric value represented as <codeph>SMALLINT</codeph> or
<codeph>BIGINT</codeph>, <codeph>FLOAT</codeph> or <codeph>DOUBLE</codeph>, or
<codeph>DECIMAL(5,2)</codeph> or <codeph>DECIMAL(20,5)</codeph>.
</p>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<codeblock>[localhost:21000] &gt; create table h (x int, s string);
[localhost:21000] &gt; insert into h values (0, 'hello'), (1,'world'), (1234567890,'antidisestablishmentarianism');
[localhost:21000] &gt; select x, fnv_hash(x) from h;
+------------+----------------------+
| x | fnv_hash(x) |
+------------+----------------------+
| 0 | -2611523532599129963 |
| 1 | 4307505193096137732 |
| 1234567890 | 3614724209955230832 |
+------------+----------------------+
[localhost:21000] &gt; select s, fnv_hash(s) from h;
+------------------------------+---------------------+
| s | fnv_hash(s) |
+------------------------------+---------------------+
| hello | 6414202926103426347 |
| world | 6535280128821139475 |
| antidisestablishmentarianism | -209330013948433970 |
+------------------------------+---------------------+
[localhost:21000] &gt; select s, abs(fnv_hash(s)) % 10 from h;
+------------------------------+-------------------------+
| s | abs(fnv_hash(s)) % 10.0 |
+------------------------------+-------------------------+
| hello | 8 |
| world | 6 |
| antidisestablishmentarianism | 4 |
+------------------------------+-------------------------+</codeblock>
<p>
For short argument values, the high-order bits of the result have relatively low
entropy:
</p>
<codeblock>[localhost:21000] &gt; create table b (x boolean);
[localhost:21000] &gt; insert into b values (true), (true), (false), (false);
[localhost:21000] &gt; select x, fnv_hash(x) from b;
+-------+---------------------+
| x | fnv_hash(x) |
+-------+---------------------+
| true | 2062020650953872396 |
| true | 2062020650953872396 |
| false | 2062021750465500607 |
| false | 2062021750465500607 |
+-------+---------------------+</codeblock>
<p>
<b>Added in:</b> Impala 1.2.2
</p>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="greatest">
<dt rev="1.4.0">
GREATEST(BIGINT a[, BIGINT b ...]), GREATEST(DOUBLE a[, DOUBLE b ...]),
GREATEST(DECIMAL(p,s) a[, DECIMAL(p,s) b ...]), GREATEST(STRING a[, STRING b ...]),
GREATEST(TIMESTAMP a[, TIMESTAMP b ...])
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Returns the largest value from a list of expressions.
<p conref="../shared/impala_common.xml#common/return_same_type"/>
</dd>
</dlentry>
<dlentry id="hex">
<dt>
HEX(BIGINT a), HEX(STRING a)
</dt>
<dd>
<b>Purpose:</b> Returns the hexadecimal representation of an integer value, or of the
characters in a string.
<p>
<b>Return type:</b> <codeph>STRING</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="is_inf">
<dt rev="1.4.0">
IS_INF(DOUBLE a)
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Tests whether a value is equal to the special value <q>inf</q>,
signifying infinity.
<p>
<b>Return type:</b> <codeph>BOOLEAN</codeph>
</p>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p conref="../shared/impala_common.xml#common/infinity_and_nan"/>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="is_nan">
<dt rev="1.4.0">
IS_NAN(DOUBLE a)
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Tests whether a value is equal to the special value <q>NaN</q>,
signifying <q>not a number</q>.
<p>
<b>Return type:</b> <codeph>BOOLEAN</codeph>
</p>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p conref="../shared/impala_common.xml#common/infinity_and_nan"/>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="least">
<dt rev="1.4.0">
LEAST(BIGINT a[, BIGINT b ...]), LEAST(DOUBLE a[, DOUBLE b ...]), LEAST(DECIMAL(p,s)
a[, DECIMAL(p,s) b ...]), LEAST(STRING a[, STRING b ...]), LEAST(TIMESTAMP a[,
TIMESTAMP b ...])
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Returns the smallest value from a list of expressions.
<p conref="../shared/impala_common.xml#common/return_same_type"/>
</dd>
</dlentry>
<dlentry id="ln">
<dt>
LN(DOUBLE a), DLOG1(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the
<xref
href="https://en.wikipedia.org/wiki/Natural_logarithm"
scope="external" format="html">natural
logarithm</xref> of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="log">
<dt>
LOG(DOUBLE base, DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the logarithm of the second argument to the specified base.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="log10">
<dt>
LOG10(DOUBLE a), DLOG10(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the logarithm of the argument to the base 10.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="log2">
<dt>
LOG2(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the logarithm of the argument to the base 2.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="max_int">
<dt rev="1.4.0">
MAX_INT(), MAX_TINYINT(), MAX_SMALLINT(), MAX_BIGINT()
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Returns the largest value of the associated integral type.
<p>
<b>Return type:</b> The same as the integral type being checked.
</p>
<p>
<b>Usage notes:</b> Use the corresponding <codeph>min_</codeph> and
<codeph>max_</codeph> functions to check if all values in a column are within the
allowed range, before copying data or altering column definitions. If not, switch to
the next higher integral type or to a <codeph>DECIMAL</codeph> with sufficient
precision.
</p>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="min_int">
<dt rev="1.4.0">
MIN_INT(), MIN_TINYINT(), MIN_SMALLINT(), MIN_BIGINT()
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Returns the smallest value of the associated integral type (a negative
number).
<p>
<b>Return type:</b> The same as the integral type being checked.
</p>
<p>
<b>Usage notes:</b> Use the corresponding <codeph>min_</codeph> and
<codeph>max_</codeph> functions to check if all values in a column are within the
allowed range, before copying data or altering column definitions. If not, switch to
the next higher integral type or to a <codeph>DECIMAL</codeph> with sufficient
precision.
</p>
</dd>
</dlentry>
<dlentry id="mod" rev="2.2.0">
<dt rev="2.2.0">
MOD(numeric_type a, same_type b)
</dt>
<dd rev="2.2.0">
<b>Purpose:</b> Returns the modulus of a number. Equivalent to the <codeph>%</codeph>
arithmetic operator. Works with any size integer type, any size floating-point type,
and <codeph>DECIMAL</codeph> with any precision and scale.
<p
conref="../shared/impala_common.xml#common/return_type_same"/>
<p conref="../shared/impala_common.xml#common/added_in_220"/>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p>
Because this function works with <codeph>DECIMAL</codeph> values, prefer it over
<codeph>fmod()</codeph> when working with fractional values. It is not subject to
the rounding errors that make <codeph>fmod()</codeph> problematic with
floating-point numbers.
</p>
<p rev="IMPALA-6202">
Query plans shows the <codeph>MOD()</codeph> function as the <codeph>%</codeph>
operator.
</p>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
The following examples show how the <codeph>mod()</codeph> function works for whole
numbers and fractional values, and how the <codeph>%</codeph> operator works the
same way. In the case of <codeph>mod(9.9,3)</codeph>, the type conversion for the
second argument results in the first argument being interpreted as
<codeph>DOUBLE</codeph>, so to produce an accurate <codeph>DECIMAL</codeph> result
requires casting the second argument or writing it as a <codeph>DECIMAL</codeph>
literal, 3.0.
</p>
<codeblock>select mod(10,3);
+-------------+
| mod(10, 3) |
+-------------+
| 1 |
+-------------+
select mod(5.5,2);
+--------------+
| mod(5.5, 2) |
+--------------+
| 1.5 |
+--------------+
select 10 % 3;
+--------+
| 10 % 3 |
+--------+
| 1 |
+--------+
select 5.5 % 2;
+---------+
| 5.5 % 2 |
+---------+
| 1.5 |
+---------+
select mod(9.9,3.3);
+---------------+
| mod(9.9, 3.3) |
+---------------+
| 0.0 |
+---------------+
select mod(9.9,3);
+--------------------+
| mod(9.9, 3) |
+--------------------+
| 0.8999996185302734 |
+--------------------+
select mod(9.9, cast(3 as decimal(2,1)));
+-----------------------------------+
| mod(9.9, cast(3 as decimal(2,1))) |
+-----------------------------------+
| 0.9 |
+-----------------------------------+
select mod(9.9,3.0);
+---------------+
| mod(9.9, 3.0) |
+---------------+
| 0.9 |
+---------------+
</codeblock>
</dd>
</dlentry>
<dlentry id="murmur_hash" rev="IMPALA-3651 2.12.0">
<dt rev="2.12.0">
MURMUR_HASH(type v)
</dt>
<dd rev="2.12.0">
<b>Purpose:</b> Returns a consistent 64-bit value derived from the input argument, for
convenience of implementing <xref
keyref="MurmurHash"> MurmurHash2</xref>
non-cryptographic hash function.
<p>
<b>Return type:</b> <codeph>BIGINT</codeph>
</p>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p>
You might use the return value in an application where you perform load balancing,
bucketing, or some other technique to divide processing or storage. This function
provides a good performance for all kinds of keys such as number, ascii string and
UTF-8. It can be recommended as general-purpose hashing function.
</p>
<p>
Regarding comparison of murmur_hash with fnv_hash, murmur_hash is based on Murmur2
hash algorithm and fnv_hash function is based on FNV-1a hash algorithm. Murmur2 and
FNV-1a can show very good randomness and performance compared with well known other
hash algorithms, but Murmur2 slightly show better randomness and performance than
FNV-1a. See
<xref keyref="hash_functions1"
>[1]</xref><xref keyref="hash_functions2">[2]</xref><xref
keyref="hash_functions1">[3]</xref>
for details.
</p>
<p>
Similar input values of different types could produce different hash values, for
example the same numeric value represented as <codeph>SMALLINT</codeph> or
<codeph>BIGINT</codeph>, <codeph>FLOAT</codeph> or <codeph>DOUBLE</codeph>, or
<codeph>DECIMAL(5,2)</codeph> or <codeph>DECIMAL(20,5)</codeph>.
</p>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<codeblock>[localhost:21000] &gt; create table h (x int, s string);
[localhost:21000] &gt; insert into h values (0, 'hello'), (1,'world'), (1234567890,'antidisestablishmentarianism');
[localhost:21000] &gt; select x, murmur_hash(x) from h;
+------------+----------------------+
| x | murmur_hash(x) |
+------------+----------------------+
| 0 | 6960269033020761575 |
| 1 | -780611581681153783 |
| 1234567890 | -5754914572385924334 |
+------------+----------------------+
[localhost:21000] &gt; select s, murmur_hash(s) from h;
+------------------------------+----------------------+
| s | murmur_hash(s) |
+------------------------------+----------------------+
| hello | 2191231550387646743 |
| world | 5568329560871645431 |
| antidisestablishmentarianism | -2261804666958489663 |
+------------------------------+----------------------+ </codeblock>
<p>
For short argument values, the high-order bits of the result have relatively higher
entropy than fnv_hash:
</p>
<codeblock>[localhost:21000] &gt; create table b (x boolean);
[localhost:21000] &gt; insert into b values (true), (true), (false), (false);
[localhost:21000] &gt; select x, murmur_hash(x) from b;
+-------+----------------------+
| x | murmur_hash(x) |
+-------+---------------------++
| true | -5720937396023583481 |
| true | -5720937396023583481 |
| false | 6351753276682545529 |
| false | 6351753276682545529 |
+-------+--------------------+-+</codeblock>
<p>
<b>Added in:</b> Impala 2.12.0
</p>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="negative">
<dt rev="2.0.1">
NEGATIVE(numeric_type a)
</dt>
<dd>
<b>Purpose:</b> Returns the argument with the sign reversed; returns a positive value
if the argument was already negative.
<p rev="2.0.1"
conref="../shared/impala_common.xml#common/return_type_same"/>
<p>
<b>Usage notes:</b> Use <codeph>-ABS(a)</codeph> instead if you need to ensure all
return values are negative.
</p>
</dd>
</dlentry>
<dlentry id="pi">
<dt rev="1.4.0">
PI()
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Returns the constant pi.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="pmod">
<dt>
PMOD(BIGINT a, BIGINT b), PMOD(DOUBLE a, DOUBLE b)
</dt>
<dd>
<b>Purpose:</b> Returns the positive modulus of a number. Primarily for
<xref href="https://issues.apache.org/jira/browse/HIVE-656"
scope="external" format="html">HiveQL
compatibility</xref>.
<p>
<b>Return type:</b> <codeph>INT</codeph> or <codeph>DOUBLE</codeph>, depending on
type of arguments
</p>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
The following examples show how the <codeph>FMOD()</codeph> function sometimes
returns a negative value depending on the sign of its arguments, and the
<codeph>PMOD()</codeph> function returns the same value as <codeph>FMOD()</codeph>,
but sometimes with the sign flipped.
</p>
<codeblock>select fmod(-5,2);
+-------------+
| fmod(-5, 2) |
+-------------+
| -1 |
+-------------+
select pmod(-5,2);
+-------------+
| pmod(-5, 2) |
+-------------+
| 1 |
+-------------+
select fmod(-5,-2);
+--------------+
| fmod(-5, -2) |
+--------------+
| -1 |
+--------------+
select pmod(-5,-2);
+--------------+
| pmod(-5, -2) |
+--------------+
| -1 |
+--------------+
select fmod(5,-2);
+-------------+
| fmod(5, -2) |
+-------------+
| 1 |
+-------------+
select pmod(5,-2);
+-------------+
| pmod(5, -2) |
+-------------+
| -1 |
+-------------+
</codeblock>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="positive">
<dt rev="2.0.1">
POSITIVE(numeric_type a)
</dt>
<dd>
<b>Purpose:</b> Returns the original argument unchanged (even if the argument is
negative).
<p rev="2.0.1"
conref="../shared/impala_common.xml#common/return_type_same"/>
<p>
<b>Usage notes:</b> Use <codeph>ABS()</codeph> instead if you need to ensure all
return values are positive.
</p>
</dd>
</dlentry>
<dlentry id="pow">
<dt rev="1.4.0">
POW(DOUBLE a, DOUBLE p), POWER(DOUBLE a, DOUBLE p), DPOW(DOUBLE a, DOUBLE p),
FPOW(DOUBLE a, DOUBLE p)
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Returns the first argument raised to the power of the second argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="precision">
<dt rev="1.4.0">
PRECISION(numeric_expression)
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Computes the precision (number of decimal digits) needed to represent
the type of the argument expression as a <codeph>DECIMAL</codeph> value.
<p
conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p>
Typically used in combination with the <codeph>SCALE()</codeph> function, to
determine the appropriate
<codeph>DECIMAL(<varname>precision</varname>,<varname>scale</varname>)</codeph> type
to declare in a <codeph>CREATE TABLE</codeph> statement or <codeph>CAST()</codeph>
function.
</p>
<p>
<b>Return type:</b> <codeph>INT</codeph>
</p>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p conref="../shared/impala_common.xml#common/precision_scale_example"
/>
</dd>
</dlentry>
<dlentry id="quotient">
<dt>
QUOTIENT(BIGINT numerator, BIGINT denominator), QUOTIENT(DOUBLE numerator, DOUBLE
denominator)
</dt>
<dd>
<b>Purpose:</b> Returns the first argument divided by the second argument, discarding
any fractional part. Avoids promoting integer arguments to <codeph>DOUBLE</codeph> as
happens with the <codeph>/</codeph> SQL operator. <ph rev="IMPALA-278">Also includes
an overload that accepts <codeph>DOUBLE</codeph> arguments, discards the fractional
part of each argument value before dividing, and again returns
<codeph>BIGINT</codeph>. With integer arguments, this function works the same as the
<codeph>DIV</codeph> operator.</ph>
<p>
<b>Return type:</b> <codeph>BIGINT</codeph>
</p>
</dd>
</dlentry>
<dlentry id="radians">
<dt>
RADIANS(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Converts argument value from degrees to radians.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="rand">
<dt>
RAND(), RAND(BIGINT seed), RANDOM(), RANDOM(BIGINT seed)
</dt>
<dd>
<b>Purpose:</b> Returns a random value between 0 and 1. After <codeph>RAND()</codeph>
is called with a seed argument, it produces a consistent random sequence based on the
seed value.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
<p>
<b>Usage notes:</b> Currently, the random sequence is reset after each query, and
multiple calls to <codeph>RAND()</codeph> within the same query return the same
value each time. For different number sequences that are different for each query,
pass a unique seed value to each call to <codeph>RAND()</codeph>. For example,
<codeph>SELECT RAND(UNIX_TIMESTAMP()) FROM ...</codeph>
</p>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
The following examples show how <codeph>rand()</codeph> can produce sequences of
varying predictability, so that you can reproduce query results involving random
values or generate unique sequences of random values for each query. When
<codeph>rand()</codeph> is called with no argument, it generates the same sequence
of values each time, regardless of the ordering of the result set. When
<codeph>rand()</codeph> is called with a constant integer, it generates a different
sequence of values, but still always the same sequence for the same seed value. If
you pass in a seed value that changes, such as the return value of the expression
<codeph>unix_timestamp(now())</codeph>, each query will use a different sequence of
random values, potentially more useful in probability calculations although more
difficult to reproduce at a later time. Therefore, the final two examples with an
unpredictable seed value also include the seed in the result set, to make it
possible to reproduce the same random sequence later.
</p>
<codeblock>select x, rand() from three_rows;
+---+-----------------------+
| x | rand() |
+---+-----------------------+
| 1 | 0.0004714746030380365 |
| 2 | 0.5895895192351144 |
| 3 | 0.4431900859080209 |
+---+-----------------------+
select x, rand() from three_rows order by x desc;
+---+-----------------------+
| x | rand() |
+---+-----------------------+
| 3 | 0.0004714746030380365 |
| 2 | 0.5895895192351144 |
| 1 | 0.4431900859080209 |
+---+-----------------------+
select x, rand(1234) from three_rows order by x;
+---+----------------------+
| x | rand(1234) |
+---+----------------------+
| 1 | 0.7377511392057646 |
| 2 | 0.009428468537250751 |
| 3 | 0.208117277924026 |
+---+----------------------+
select x, rand(1234) from three_rows order by x desc;
+---+----------------------+
| x | rand(1234) |
+---+----------------------+
| 3 | 0.7377511392057646 |
| 2 | 0.009428468537250751 |
| 1 | 0.208117277924026 |
+---+----------------------+
select x, unix_timestamp(now()), rand(unix_timestamp(now()))
from three_rows order by x;
+---+-----------------------+-----------------------------+
| x | unix_timestamp(now()) | rand(unix_timestamp(now())) |
+---+-----------------------+-----------------------------+
| 1 | 1440777752 | 0.002051228658320023 |
| 2 | 1440777752 | 0.5098743483004506 |
| 3 | 1440777752 | 0.9517714925817081 |
+---+-----------------------+-----------------------------+
select x, unix_timestamp(now()), rand(unix_timestamp(now()))
from three_rows order by x desc;
+---+-----------------------+-----------------------------+
| x | unix_timestamp(now()) | rand(unix_timestamp(now())) |
+---+-----------------------+-----------------------------+
| 3 | 1440777761 | 0.9985985015512437 |
| 2 | 1440777761 | 0.3251255333074953 |
| 1 | 1440777761 | 0.02422675025846192 |
+---+-----------------------+-----------------------------+
</codeblock>
</dd>
</dlentry>
<dlentry id="round">
<dt>
ROUND(DOUBLE a), ROUND(DOUBLE a, INT d), ROUND(DECIMAL a, int_type d), DROUND(DOUBLE
a), DROUND(DOUBLE a, INT d), DROUND(DECIMAL(p,s) a, int_type d)
</dt>
<dd>
<b>Purpose:</b> Rounds a floating-point value. By default (with a single argument),
rounds to the nearest integer. Values ending in .5 are rounded up for positive
numbers, down for negative numbers (that is, away from zero). The optional second
argument specifies how many digits to leave after the decimal point; values greater
than zero produce a floating-point return value rounded to the requested number of
digits to the right of the decimal point.
<p rev="1.4.0">
<b>Return type:</b> Same as the input type
</p>
</dd>
</dlentry>
<dlentry rev="1.4.0" id="scale">
<dt rev="1.4.0">
SCALE(numeric_expression)
</dt>
<dd rev="1.4.0">
<b>Purpose:</b> Computes the scale (number of decimal digits to the right of the
decimal point) needed to represent the type of the argument expression as a
<codeph>DECIMAL</codeph> value.
<p
conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p>
Typically used in combination with the <codeph>PRECISION()</codeph> function, to
determine the appropriate
<codeph>DECIMAL(<varname>precision</varname>,<varname>scale</varname>)</codeph> type
to declare in a <codeph>CREATE TABLE</codeph> statement or <codeph>CAST()</codeph>
function.
</p>
<p>
<b>Return type:</b> <codeph>INT</codeph>
</p>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p conref="../shared/impala_common.xml#common/precision_scale_example"
/>
</dd>
</dlentry>
<dlentry id="sign">
<dt>
SIGN(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns -1, 0, or 1 to indicate the signedness of the argument value.
<p>
<b>Return type:</b> <codeph>INT</codeph>
</p>
</dd>
</dlentry>
<dlentry id="sin">
<dt>
SIN(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the sine of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="sinh" rev="2.3.0 IMPALA-1771">
<dt rev="2.3.0 IMPALA-1771">
SINH(DOUBLE a)
</dt>
<dd rev="2.3.0 IMPALA-1771">
<b>Purpose:</b> Returns the hyperbolic sine of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="sqrt">
<dt>
SQRT(DOUBLE a), DSQRT(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the square root of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="tan">
<dt>
TAN(DOUBLE a)
</dt>
<dd>
<b>Purpose:</b> Returns the tangent of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry id="tanh" rev="2.3.0 IMPALA-1771">
<dt rev="2.3.0 IMPALA-1771">
TANH(DOUBLE a)
</dt>
<dd rev="2.3.0 IMPALA-1771">
<b>Purpose:</b> Returns the hyperbolic tangent of the argument.
<p>
<b>Return type:</b> <codeph>DOUBLE</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="2.3.0" id="truncate">
<dt rev="2.3.0">
TRUNCATE(DOUBLE_or_DECIMAL a[, digits_to_leave]), DTRUNC(DOUBLE_or_DECIMAL a[,
digits_to_leave]), TRUNC(DOUBLE_or_DECIMAL a[, digits_to_leave])
</dt>
<dd rev="2.3.0">
<b>Purpose:</b> Removes some or all fractional digits from a numeric value.
<p>
<b>Arguments:</b> With a single floating-point argument, removes all fractional
digits, leaving an integer value. The optional second argument specifies the number
of fractional digits to include in the return value, and only applies when the
argument type is <codeph>DECIMAL</codeph>. A second argument of 0 truncates to a
whole integer value. A second argument of negative N sets N digits to 0 on the left
side of the decimal
</p>
<p rev="2.10.0 IMPALA-5529">
<b>Scale argument:</b> The scale argument applies only when truncating
<codeph>DECIMAL</codeph> values. It is an integer specifying how many significant
digits to leave to the right of the decimal point. A scale argument of 0 truncates
to a whole integer value. A scale argument of negative N sets N digits to 0 on the
left side of the decimal point.
</p>
<p>
<codeph>TRUNCATE()</codeph>, <codeph>DTRUNC()</codeph>,
<ph
rev="2.10.0 IMPALA-5529">and <codeph>TRUNC()</codeph></ph> are
aliases for the same function.
</p>
<p>
<b>Return type:</b> Same as the input type
</p>
<p>
<b>Added in:</b> The <codeph>TRUNC()</codeph> alias was added in
<keyword keyref="impala210_full"/>.
</p>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p rev="2.10.0 IMPALA-5529">
You can also pass a <codeph>DOUBLE</codeph> argument, or <codeph>DECIMAL</codeph>
argument with optional scale, to the <codeph>DTRUNC()</codeph> or
<codeph>TRUNCATE</codeph> functions. Using the <codeph>TRUNC()</codeph> function for
numeric values is common with other industry-standard database systems, so you might
find such <codeph>TRUNC()</codeph> calls in code that you are porting to Impala.
</p>
<p>
The <codeph>TRUNC()</codeph> function also has a signature that applies to
<codeph>TIMESTAMP</codeph> values. See
<xref
keyref="datetime_functions"/> for details.
</p>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
The following examples demonstrate the <codeph>TRUNCATE()</codeph> and
<codeph>DTRUNC()</codeph> signatures for this function:
</p>
<codeblock>select truncate(3.45);
+----------------+
| truncate(3.45) |
+----------------+
| 3 |
+----------------+
select truncate(-3.45);
+-----------------+
| truncate(-3.45) |
+-----------------+
| -3 |
+-----------------+
select truncate(3.456,1);
+--------------------+
| truncate(3.456, 1) |
+--------------------+
| 3.4 |
+--------------------+
select dtrunc(3.456,1);
+------------------+
| dtrunc(3.456, 1) |
+------------------+
| 3.4 |
+------------------+
select truncate(3.456,2);
+--------------------+
| truncate(3.456, 2) |
+--------------------+
| 3.45 |
+--------------------+
select truncate(3.456,7);
+--------------------+
| truncate(3.456, 7) |
+--------------------+
| 3.4560000 |
+--------------------+
</codeblock>
<p rev="2.10.0 IMPALA-5529">
The following examples demonstrate using <codeph>trunc()</codeph> with
<codeph>DECIMAL</codeph> or <codeph>DOUBLE</codeph> values, and with an optional
scale argument for <codeph>DECIMAL</codeph> values. (The behavior is the same for
the <codeph>truncate()</codeph> and <codeph>dtrunc()</codeph> aliases also.)
</p>
<codeblock rev="2.10.0 IMPALA-5529">
create table t1 (d decimal(20,7));
-- By default, no digits to the right of the decimal point.
insert into t1 values (1.1), (2.22), (3.333), (4.4444), (5.55555);
select trunc(d) from t1 order by d;
+----------+
| trunc(d) |
+----------+
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
+----------+
-- 1 digit to the right of the decimal point.
select trunc(d,1) from t1 order by d;
+-------------+
| trunc(d, 1) |
+-------------+
| 1.1 |
| 2.2 |
| 3.3 |
| 4.4 |
| 5.5 |
+-------------+
-- 2 digits to the right of the decimal point,
-- including trailing zeroes if needed.
select trunc(d,2) from t1 order by d;
+-------------+
| trunc(d, 2) |
+-------------+
| 1.10 |
| 2.22 |
| 3.33 |
| 4.44 |
| 5.55 |
+-------------+
insert into t1 values (9999.9999), (8888.8888);
-- Negative scale truncates digits to the left
-- of the decimal point.
select trunc(d,-2) from t1 where d > 100 order by d;
+--------------+
| trunc(d, -2) |
+--------------+
| 8800 |
| 9900 |
+--------------+
-- The scale of the result is adjusted to match the
-- scale argument.
select trunc(d,2),
precision(trunc(d,2)) as p,
scale(trunc(d,2)) as s
from t1 order by d;
+-------------+----+---+
| trunc(d, 2) | p | s |
+-------------+----+---+
| 1.10 | 15 | 2 |
| 2.22 | 15 | 2 |
| 3.33 | 15 | 2 |
| 4.44 | 15 | 2 |
| 5.55 | 15 | 2 |
| 8888.88 | 15 | 2 |
| 9999.99 | 15 | 2 |
+-------------+----+---+
</codeblock>
<codeblock rev="2.10.0 IMPALA-5529">
create table dbl (d double);
insert into dbl values
(1.1), (2.22), (3.333), (4.4444), (5.55555),
(8888.8888), (9999.9999);
-- With double values, there is no optional scale argument.
select trunc(d) from dbl order by d;
+----------+
| trunc(d) |
+----------+
| 1 |
| 2 |
| 3 |
| 4 |
| 5 |
| 8888 |
| 9999 |
+----------+
</codeblock>
</dd>
</dlentry>
<dlentry id="unhex">
<dt>
UNHEX(STRING a)
</dt>
<dd>
<b>Purpose:</b> Returns a string of characters with ASCII values corresponding to
pairs of hexadecimal digits in the argument.
<p>
<b>Return type:</b> <codeph>STRING</codeph>
</p>
</dd>
</dlentry>
<dlentry id="width_bucket">
<dt>
WIDTH_BUCKET(DECIMAL expr, DECIMAL min_value, DECIMAL max_value, INT num_buckets)
</dt>
<dd>
<b>Purpose:</b> Returns the bucket number in which the <codeph>expr</codeph> value
would fall in the histogram where its range between <codeph>min_value</codeph> and
<codeph>max_value</codeph> is divided into <codeph>num_buckets</codeph> buckets of
identical sizes.
</dd>
<dd>
The function returns:
<ul>
<li>
<codeph>NULL</codeph> if any argument is <codeph>NULL</codeph>.
</li>
<li>
<codeph>0</codeph> if <codeph>expr</codeph> &lt; <codeph>min_value</codeph>.
</li>
<li>
<codeph>num_buckets + 1</codeph> if <codeph>expr</codeph> >=
<codeph>max_val</codeph>.
</li>
<li>
If none of the above, the bucket number where <codeph>expr</codeph> falls.
</li>
</ul>
<p>
<b>Arguments:</b>The following rules apply to the arguments.
<ul>
<li>
<codeph>min_val</codeph> is the minimum value of the histogram range.
</li>
<li>
<codeph>max_val</codeph> is the maximum value of the histogram range.
</li>
<li>
<codeph>num_buckets</codeph> must be greater than <codeph>0</codeph>.
</li>
<li>
<codeph>min_value</codeph> must be less than <codeph>max_value</codeph>.
</li>
</ul>
</p>
<p>
<b>Usage notes:</b>
</p>
<p>
Each bucket contains values equal to or greater than the base value of that bucket
and less than the base value of the next bucket. For example, with
<codeph>width_bucket(8, 1, 10, 3)</codeph>, the bucket ranges are actually the 0th
"underflow bucket" with the range (-infinity to 0.999...), (1 to 3.999...), (4, to
6.999...), (7 to 9.999...), and the "overflow bucket" with the range (10 to
infinity).
</p>
<p>
<b>Return type:</b> <codeph>BIGINT</codeph>
</p>
<p>
<b>Added in:</b> <keyword keyref="impala31"/>.
</p>
<p>
<b>Examples:</b>
</p>
<p>
The below function creates <codeph>3</codeph> buckets between the range of
<codeph>1</codeph> and <codeph>20</codeph> with the bucket width of 6.333, and
returns <codeph>2</codeph> for the bucket #2 where the value <codeph>8</codeph>
falls in:
<codeblock>width_bucket(8, 1, 20, 3)</codeblock>
</p>
<p>
The below statement returns a list of accounts with the energy spending and the
spending bracket each account falls in, between 0 and 11. Bucket 0 (underflow
bucket) will be assigned to the accounts whose energy spendings are less than $50.
Bucket 11 (overflow bucket) will be assigned to the accounts whose energy spendings
are more than or equal to $1000.
</p>
<codeblock>SELECT account, invoice_amount, WIDTH_BUCKET(invoice_amount,50,1000,10)
FROM invoices_june2018
ORDER BY 3;</codeblock>
</dd>
</dlentry>
</dl>
</conbody>
</concept>
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