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impala/docs/topics/impala_string_functions.xml
John Russell f3820e6205 MPALA-3402: [DOCS] Remove CDH- JIRA numbers from rev= 
For history and tracking purposes, there are many
instances of rev="CDH-1234" for various CDH- JIRA
numbers. This produces no visible output, it's just
FYI for the person editing the source. Removing all
these now from the upstream doc source, so as not
to have "CDH" all through the doc source files.

Change-Id: I29089e5a31cd72e876b2ccb8375d1c10693c6aba
Reviewed-on: http://gerrit.cloudera.org:8080/6349
Reviewed-by: Ambreen Kazi <ambreen.kazi@cloudera.com>
Reviewed-by: John Russell <jrussell@cloudera.com>
Tested-by: Impala Public Jenkins
2017-03-10 23:56:51 +00:00

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<?xml version="1.0" encoding="UTF-8"?><!--
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements. See the NOTICE file
distributed with this work for additional information
regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.
-->
<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="string_functions">
<title>Impala String Functions</title>
<titlealts audience="PDF"><navtitle>String 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 rev="2.0.0">
String functions are classified as those primarily accepting or returning <codeph>STRING</codeph>,
<codeph>VARCHAR</codeph>, or <codeph>CHAR</codeph> data types, for example to measure the length of a string
or concatenate two strings together.
<ul>
<li>
All the functions that accept <codeph>STRING</codeph> arguments also accept the <codeph>VARCHAR</codeph>
and <codeph>CHAR</codeph> types introduced in Impala 2.0.
</li>
<li>
Whenever <codeph>VARCHAR</codeph> or <codeph>CHAR</codeph> values are passed to a function that returns a
string value, the return type is normalized to <codeph>STRING</codeph>. For example, a call to
<codeph>concat()</codeph> with a mix of <codeph>STRING</codeph>, <codeph>VARCHAR</codeph>, and
<codeph>CHAR</codeph> arguments produces a <codeph>STRING</codeph> result.
</li>
</ul>
</p>
<p conref="../shared/impala_common.xml#common/related_info"/>
<p>
The string functions operate mainly on these data types: <xref href="impala_string.xml#string"/>,
<xref href="impala_varchar.xml#varchar"/>, and <xref href="impala_char.xml#char"/>.
</p>
<p>
<b>Function reference:</b>
</p>
<p>
Impala supports the following string functions:
</p>
<dl>
<dlentry id="ascii">
<dt>
<codeph>ascii(string str)</codeph>
</dt>
<dd>
<indexterm audience="hidden">ascii() function</indexterm>
<b>Purpose:</b> Returns the numeric ASCII code of the first character of the argument.
<p>
<b>Return type:</b> <codeph>int</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="2.3.0" id="btrim">
<dt>
<codeph>btrim(string a)</codeph>,
<codeph>btrim(string a, string chars_to_trim)</codeph>
</dt>
<dd>
<indexterm audience="hidden">btrim() function</indexterm>
<b>Purpose:</b> Removes all instances of one or more characters
from the start and end of a <codeph>STRING</codeph> value.
By default, removes only spaces.
If a non-<codeph>NULL</codeph> optional second argument is specified, the function removes all
occurrences of characters in that second argument from the beginning and
end of the string.
<p><b>Return type:</b> <codeph>string</codeph></p>
<p conref="../shared/impala_common.xml#common/added_in_230"/>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
The following examples show the default <codeph>btrim()</codeph> behavior,
and what changes when you specify the optional second argument.
All the examples bracket the output value with <codeph>[ ]</codeph>
so that you can see any leading or trailing spaces in the <codeph>btrim()</codeph> result.
By default, the function removes and number of both leading and trailing spaces.
When the second argument is specified, any number of occurrences of any
character in the second argument are removed from the start and end of the
input string; in this case, spaces are not removed (unless they are part of the second
argument) and any instances of the characters are not removed if they do not come
right at the beginning or end of the string.
</p>
<codeblock>-- Remove multiple spaces before and one space after.
select concat('[',btrim(' hello '),']');
+---------------------------------------+
| concat('[', btrim(' hello '), ']') |
+---------------------------------------+
| [hello] |
+---------------------------------------+
-- Remove any instances of x or y or z at beginning or end. Leave spaces alone.
select concat('[',btrim('xy hello zyzzxx','xyz'),']');
+------------------------------------------------------+
| concat('[', btrim('xy hello zyzzxx', 'xyz'), ']') |
+------------------------------------------------------+
| [ hello ] |
+------------------------------------------------------+
-- Remove any instances of x or y or z at beginning or end.
-- Leave x, y, z alone in the middle of the string.
select concat('[',btrim('xyhelxyzlozyzzxx','xyz'),']');
+----------------------------------------------------+
| concat('[', btrim('xyhelxyzlozyzzxx', 'xyz'), ']') |
+----------------------------------------------------+
| [helxyzlo] |
+----------------------------------------------------+
</codeblock>
</dd>
</dlentry>
<dlentry rev="1.3.0" id="char_length">
<dt>
<codeph>char_length(string a), <ph rev="1.3.0" id="character_length">character_length(string a)</ph></codeph>
</dt>
<dd>
<indexterm audience="hidden">char_length() function</indexterm>
<indexterm audience="hidden">character_length() function</indexterm>
<b>Purpose:</b> Returns the length in characters of the argument string. Aliases for the
<codeph>length()</codeph> function.
<p>
<b>Return type:</b> <codeph>int</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="2.3.0" id="chr">
<dt>
<codeph>chr(int character_code)</codeph>
</dt>
<dd>
<indexterm audience="hidden">chr() function</indexterm>
<b>Purpose:</b> Returns a character specified by a decimal code point value.
The interpretation and display of the resulting character depends on your system locale.
Because consistent processing of Impala string values is only guaranteed
for values within the ASCII range, only use this function for values
corresponding to ASCII characters.
In particular, parameter values greater than 255 return an empty string.
<p><b>Return type:</b> <codeph>string</codeph></p>
<p>
<b>Usage notes:</b> Can be used as the inverse of the <codeph>ascii()</codeph> function, which
converts a character to its numeric ASCII code.
</p>
<p conref="../shared/impala_common.xml#common/added_in_230"/>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<codeblock>SELECT chr(65);
+---------+
| chr(65) |
+---------+
| A |
+---------+
SELECT chr(97);
+---------+
| chr(97) |
+---------+
| a |
+---------+
</codeblock>
</dd>
</dlentry>
<dlentry id="concat">
<dt>
<codeph>concat(string a, string b...)</codeph>
</dt>
<dd>
<indexterm audience="hidden">concat() function</indexterm>
<b>Purpose:</b> Returns a single string representing all the argument values joined together.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
<p conref="../shared/impala_common.xml#common/concat_blurb"/>
</dd>
</dlentry>
<dlentry id="concat_ws">
<dt>
<codeph>concat_ws(string sep, string a, string b...)</codeph>
</dt>
<dd>
<indexterm audience="hidden">concat_ws() function</indexterm>
<b>Purpose:</b> Returns a single string representing the second and following argument values joined
together, delimited by a specified separator.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
<p conref="../shared/impala_common.xml#common/concat_blurb"/>
</dd>
</dlentry>
<dlentry id="find_in_set">
<dt>
<codeph>find_in_set(string str, string strList)</codeph>
</dt>
<dd>
<indexterm audience="hidden">find_in_set() function</indexterm>
<b>Purpose:</b> Returns the position (starting from 1) of the first occurrence of a specified string
within a comma-separated string. Returns <codeph>NULL</codeph> if either argument is
<codeph>NULL</codeph>, 0 if the search string is not found, or 0 if the search string contains a comma.
<p>
<b>Return type:</b> <codeph>int</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="1.2" id="group_concat">
<dt>
<codeph>group_concat(string s [, string sep])</codeph>
</dt>
<dd>
<indexterm audience="hidden">group_concat() function</indexterm>
<b>Purpose:</b> Returns a single string representing the argument value concatenated together for each
row of the result set. If the optional separator string is specified, the separator is added between each
pair of concatenated values.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
<p conref="../shared/impala_common.xml#common/concat_blurb"/>
<p>
By default, returns a single string covering the whole result set. To include other columns or values
in the result set, or to produce multiple concatenated strings for subsets of rows, include a
<codeph>GROUP BY</codeph> clause in the query.
</p>
<p>
Strictly speaking, <codeph>group_concat()</codeph> is an aggregate function, not a scalar
function like the others in this list.
For additional details and examples, see <xref href="impala_group_concat.xml#group_concat"/>.
</p>
</dd>
</dlentry>
<dlentry rev="1.2" id="initcap">
<dt>
<codeph>initcap(string str)</codeph>
</dt>
<dd>
<indexterm audience="hidden">initcap() function</indexterm>
<b>Purpose:</b> Returns the input string with the first letter capitalized.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="instr">
<dt>
<codeph>instr(string str, string substr)</codeph>
</dt>
<dd>
<indexterm audience="hidden">instr() function</indexterm>
<b>Purpose:</b> Returns the position (starting from 1) of the first occurrence of a substring within a
longer string.
<p>
<b>Return type:</b> <codeph>int</codeph>
</p>
</dd>
</dlentry>
<dlentry id="length">
<dt>
<codeph>length(string a)</codeph>
</dt>
<dd>
<indexterm audience="hidden">length() function</indexterm>
<b>Purpose:</b> Returns the length in characters of the argument string.
<p>
<b>Return type:</b> <codeph>int</codeph>
</p>
</dd>
</dlentry>
<dlentry id="locate">
<dt>
<codeph>locate(string substr, string str[, int pos])</codeph>
</dt>
<dd>
<indexterm audience="hidden">locate() function</indexterm>
<b>Purpose:</b> Returns the position (starting from 1) of the first occurrence of a substring within a
longer string, optionally after a particular position.
<p>
<b>Return type:</b> <codeph>int</codeph>
</p>
</dd>
</dlentry>
<dlentry id="lower">
<dt>
<codeph>lower(string a), <ph id="lcase">lcase(string a)</ph> </codeph>
</dt>
<dd>
<indexterm audience="hidden">lower() function</indexterm>
<b>Purpose:</b> Returns the argument string converted to all-lowercase.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p conref="../shared/impala_common.xml#common/case_insensitive_comparisons_tip"/>
</dd>
</dlentry>
<dlentry id="lpad">
<dt>
<codeph>lpad(string str, int len, string pad)</codeph>
</dt>
<dd>
<indexterm audience="hidden">lpad() function</indexterm>
<b>Purpose:</b> Returns a string of a specified length, based on the first argument string. If the
specified string is too short, it is padded on the left with a repeating sequence of the characters from
the pad string. If the specified string is too long, it is truncated on the right.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="ltrim">
<dt>
<codeph>ltrim(string a)</codeph>
</dt>
<dd>
<indexterm audience="hidden">ltrim() function</indexterm>
<b>Purpose:</b> Returns the argument string with any leading spaces removed from the left side.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="parse_url">
<dt>
<codeph>parse_url(string urlString, string partToExtract [, string keyToExtract])</codeph>
</dt>
<dd>
<indexterm audience="hidden">parse_url() function</indexterm>
<b>Purpose:</b> Returns the portion of a URL corresponding to a specified part. The part argument can be
<codeph>'PROTOCOL'</codeph>, <codeph>'HOST'</codeph>, <codeph>'PATH'</codeph>, <codeph>'REF'</codeph>,
<codeph>'AUTHORITY'</codeph>, <codeph>'FILE'</codeph>, <codeph>'USERINFO'</codeph>, or
<codeph>'QUERY'</codeph>. Uppercase is required for these literal values. When requesting the
<codeph>QUERY</codeph> portion of the URL, you can optionally specify a key to retrieve just the
associated value from the key-value pairs in the query string.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
<p>
<b>Usage notes:</b> This function is important for the traditional Hadoop use case of interpreting web
logs. For example, if the web traffic data features raw URLs not divided into separate table columns,
you can count visitors to a particular page by extracting the <codeph>'PATH'</codeph> or
<codeph>'FILE'</codeph> field, or analyze search terms by extracting the corresponding key from the
<codeph>'QUERY'</codeph> field.
</p>
</dd>
</dlentry>
<dlentry id="regexp_extract">
<dt>
<codeph>regexp_extract(string subject, string pattern, int index)</codeph>
</dt>
<dd>
<indexterm audience="hidden">regexp_extract() function</indexterm>
<b>Purpose:</b> Returns the specified () group from a string based on a regular expression pattern. Group
0 refers to the entire extracted string, while group 1, 2, and so on refers to the first, second, and so
on <codeph>(...)</codeph> portion.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
<p conref="../shared/impala_common.xml#common/regexp_re2"/>
<p conref="../shared/impala_common.xml#common/regexp_re2_warning"/>
<p conref="../shared/impala_common.xml#common/regexp_escapes"/>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
This example shows how group 0 matches the full pattern string, including the portion outside any
<codeph>()</codeph> group:
</p>
<codeblock>[localhost:21000] &gt; select regexp_extract('abcdef123ghi456jkl','.*?(\\d+)',0);
+------------------------------------------------------+
| regexp_extract('abcdef123ghi456jkl', '.*?(\\d+)', 0) |
+------------------------------------------------------+
| abcdef123ghi456 |
+------------------------------------------------------+
Returned 1 row(s) in 0.11s</codeblock>
<p>
This example shows how group 1 matches just the contents inside the first <codeph>()</codeph> group in
the pattern string:
</p>
<codeblock>[localhost:21000] &gt; select regexp_extract('abcdef123ghi456jkl','.*?(\\d+)',1);
+------------------------------------------------------+
| regexp_extract('abcdef123ghi456jkl', '.*?(\\d+)', 1) |
+------------------------------------------------------+
| 456 |
+------------------------------------------------------+
Returned 1 row(s) in 0.11s</codeblock>
<p rev="2.0.0">
Unlike in earlier Impala releases, the regular expression library used in Impala 2.0 and later supports
the <codeph>.*?</codeph> idiom for non-greedy matches. This example shows how a pattern string starting
with <codeph>.*?</codeph> matches the shortest possible portion of the source string, returning the
rightmost set of lowercase letters. A pattern string both starting and ending with <codeph>.*?</codeph>
finds two potential matches of equal length, and returns the first one found (the leftmost set of
lowercase letters).
</p>
<codeblock>[localhost:21000] &gt; select regexp_extract('AbcdBCdefGHI','.*?([[:lower:]]+)',1);
+--------------------------------------------------------+
| regexp_extract('abcdbcdefghi', '.*?([[:lower:]]+)', 1) |
+--------------------------------------------------------+
| def |
+--------------------------------------------------------+
[localhost:21000] &gt; select regexp_extract('AbcdBCdefGHI','.*?([[:lower:]]+).*?',1);
+-----------------------------------------------------------+
| regexp_extract('abcdbcdefghi', '.*?([[:lower:]]+).*?', 1) |
+-----------------------------------------------------------+
| bcd |
+-----------------------------------------------------------+
</codeblock>
</dd>
</dlentry>
<dlentry rev="2.3.0" id="regexp_like">
<dt>
<codeph>regexp_like(string source, string pattern[, string options])</codeph>
</dt>
<dd>
<indexterm audience="hidden">regexp_like() function</indexterm>
<b>Purpose:</b> Returns <codeph>true</codeph> or <codeph>false</codeph> to indicate
whether the source string contains anywhere inside it the regular expression given by the pattern.
The optional third argument consists of letter flags that change how the match is performed,
such as <codeph>i</codeph> for case-insensitive matching.
<p conref="../shared/impala_common.xml#common/syntax_blurb"/>
<p>
The flags that you can include in the optional third argument are:
</p>
<ul>
<li>
<codeph>c</codeph>: Case-sensitive matching (the default).
</li>
<li>
<codeph>i</codeph>: Case-insensitive matching. If multiple instances of <codeph>c</codeph> and <codeph>i</codeph>
are included in the third argument, the last such option takes precedence.
</li>
<li>
<codeph>m</codeph>: Multi-line matching. The <codeph>^</codeph> and <codeph>$</codeph>
operators match the start or end of any line within the source string, not the
start and end of the entire string.
</li>
<li>
<codeph>n</codeph>: Newline matching. The <codeph>.</codeph> operator can match the
newline character. A repetition operator such as <codeph>.*</codeph> can
match a portion of the source string that spans multiple lines.
</li>
</ul>
<p>
<b>Return type:</b> <codeph>boolean</codeph>
</p>
<p conref="../shared/impala_common.xml#common/regexp_re2"/>
<p conref="../shared/impala_common.xml#common/regexp_re2_warning"/>
<p conref="../shared/impala_common.xml#common/regexp_escapes"/>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
This example shows how <codeph>regexp_like()</codeph> can test for the existence
of various kinds of regular expression patterns within a source string:
</p>
<codeblock><![CDATA[
-- Matches because the 'f' appears somewhere in 'foo'.
select regexp_like('foo','f');
+-------------------------+
| regexp_like('foo', 'f') |
+-------------------------+
| true |
+-------------------------+
-- Does not match because the comparison is case-sensitive by default.
select regexp_like('foo','F');
+-------------------------+
| regexp_like('foo', 'f') |
+-------------------------+
| false |
+-------------------------+
-- The 3rd argument can change the matching logic, such as 'i' meaning case-insensitive.
select regexp_like('foo','F','i');
+------------------------------+
| regexp_like('foo', 'f', 'i') |
+------------------------------+
| true |
+------------------------------+
-- The familiar regular expression notations work, such as ^ and $ anchors...
select regexp_like('foo','f$');
+--------------------------+
| regexp_like('foo', 'f$') |
+--------------------------+
| false |
+--------------------------+
select regexp_like('foo','o$');
+--------------------------+
| regexp_like('foo', 'o$') |
+--------------------------+
| true |
+--------------------------+
-- ...and repetition operators such as * and +
select regexp_like('foooooobar','fo+b');
+-----------------------------------+
| regexp_like('foooooobar', 'fo+b') |
+-----------------------------------+
| true |
+-----------------------------------+
select regexp_like('foooooobar','fx*y*o*b');
+---------------------------------------+
| regexp_like('foooooobar', 'fx*y*o*b') |
+---------------------------------------+
| true |
+---------------------------------------+
]]>
</codeblock>
</dd>
</dlentry>
<dlentry id="regexp_replace">
<dt>
<codeph>regexp_replace(string initial, string pattern, string replacement)</codeph>
</dt>
<dd>
<indexterm audience="hidden">regexp_replace() function</indexterm>
<b>Purpose:</b> Returns the initial argument with the regular expression pattern replaced by the final
argument string.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
<p conref="../shared/impala_common.xml#common/regexp_re2"/>
<p conref="../shared/impala_common.xml#common/regexp_re2_warning"/>
<p conref="../shared/impala_common.xml#common/regexp_escapes"/>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
These examples show how you can replace parts of a string matching a pattern with replacement text,
which can include backreferences to any <codeph>()</codeph> groups in the pattern string. The
backreference numbers start at 1, and any <codeph>\</codeph> characters must be escaped as
<codeph>\\</codeph>.
</p>
<p>
Replace a character pattern with new text:
</p>
<codeblock>[localhost:21000] &gt; select regexp_replace('aaabbbaaa','b+','xyz');
+------------------------------------------+
| regexp_replace('aaabbbaaa', 'b+', 'xyz') |
+------------------------------------------+
| aaaxyzaaa |
+------------------------------------------+
Returned 1 row(s) in 0.11s</codeblock>
<p>
Replace a character pattern with substitution text that includes the original matching text:
</p>
<codeblock>[localhost:21000] &gt; select regexp_replace('aaabbbaaa','(b+)','&lt;\\1&gt;');
+----------------------------------------------+
| regexp_replace('aaabbbaaa', '(b+)', '&lt;\\1&gt;') |
+----------------------------------------------+
| aaa&lt;bbb&gt;aaa |
+----------------------------------------------+
Returned 1 row(s) in 0.11s</codeblock>
<p>
Remove all characters that are not digits:
</p>
<codeblock>[localhost:21000] &gt; select regexp_replace('123-456-789','[^[:digit:]]','');
+---------------------------------------------------+
| regexp_replace('123-456-789', '[^[:digit:]]', '') |
+---------------------------------------------------+
| 123456789 |
+---------------------------------------------------+
Returned 1 row(s) in 0.12s</codeblock>
</dd>
</dlentry>
<dlentry id="repeat">
<dt>
<codeph>repeat(string str, int n)</codeph>
</dt>
<dd>
<indexterm audience="hidden">repeat() function</indexterm>
<b>Purpose:</b> Returns the argument string repeated a specified number of times.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="reverse">
<dt>
<codeph>reverse(string a)</codeph>
</dt>
<dd>
<indexterm audience="hidden">reverse() function</indexterm>
<b>Purpose:</b> Returns the argument string with characters in reversed order.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="rpad">
<dt>
<codeph>rpad(string str, int len, string pad)</codeph>
</dt>
<dd>
<indexterm audience="hidden">rpad() function</indexterm>
<b>Purpose:</b> Returns a string of a specified length, based on the first argument string. If the
specified string is too short, it is padded on the right with a repeating sequence of the characters from
the pad string. If the specified string is too long, it is truncated on the right.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="rtrim">
<dt>
<codeph>rtrim(string a)</codeph>
</dt>
<dd>
<indexterm audience="hidden">rtrim() function</indexterm>
<b>Purpose:</b> Returns the argument string with any trailing spaces removed from the right side.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="space">
<dt>
<codeph>space(int n)</codeph>
</dt>
<dd>
<indexterm audience="hidden">space() function</indexterm>
<b>Purpose:</b> Returns a concatenated string of the specified number of spaces. Shorthand for
<codeph>repeat(' ',<varname>n</varname>)</codeph>.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry rev="2.3.0 IMPALA-2084" id="split_part">
<dt>
<codeph>split_part(string source, string delimiter, bigint n)</codeph>
</dt>
<dd>
<indexterm audience="hidden">split_part() function</indexterm>
<b>Purpose:</b> Returns the nth field within a delimited string.
The fields are numbered starting from 1.
The delimiter can consist of multiple characters, not just a
single character. All matching of the delimiter is done exactly, not using any
regular expression patterns.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
<p conref="../shared/impala_common.xml#common/regexp_re2"/>
<p conref="../shared/impala_common.xml#common/regexp_re2_warning"/>
<p conref="../shared/impala_common.xml#common/regexp_escapes"/>
<p conref="../shared/impala_common.xml#common/example_blurb"/>
<p>
These examples show how to retrieve the nth field from a delimited string:
</p>
<codeblock><![CDATA[
select split_part('x,y,z',',',1);
+-----------------------------+
| split_part('x,y,z', ',', 1) |
+-----------------------------+
| x |
+-----------------------------+
select split_part('x,y,z',',',2);
+-----------------------------+
| split_part('x,y,z', ',', 2) |
+-----------------------------+
| y |
+-----------------------------+
select split_part('x,y,z',',',3);
+-----------------------------+
| split_part('x,y,z', ',', 3) |
+-----------------------------+
| z |
+-----------------------------+
</codeblock>
<p>
These examples show what happens for out-of-range field positions.
Specifying a value less than 1 produces an error. Specifying a value
greater than the number of fields returns a zero-length string
(which is not the same as <codeph>NULL</codeph>).
</p>
<codeblock><![CDATA[
select split_part('x,y,z',',',0);
ERROR: Invalid field position: 0
with t1 as (select split_part('x,y,z',',',4) nonexistent_field)
select
nonexistent_field
, concat('[',nonexistent_field,']')
, length(nonexistent_field);
from t1
+-------------------+-------------------------------------+---------------------------+
| nonexistent_field | concat('[', nonexistent_field, ']') | length(nonexistent_field) |
+-------------------+-------------------------------------+---------------------------+
| | [] | 0 |
+-------------------+-------------------------------------+---------------------------+
</codeblock>
<p>
These examples show how the delimiter can be a multi-character value:
</p>
<codeblock><![CDATA[
select split_part('one***two***three','***',2);
+-------------------------------------------+
| split_part('one***two***three', '***', 2) |
+-------------------------------------------+
| two |
+-------------------------------------------+
select split_part('one\|/two\|/three','\|/',3);
+-------------------------------------------+
| split_part('one\|/two\|/three', '\|/', 3) |
+-------------------------------------------+
| three |
+-------------------------------------------+
]]>
</codeblock>
</dd>
</dlentry>
<dlentry id="strleft">
<dt>
<codeph>strleft(string a, int num_chars)</codeph>
</dt>
<dd>
<indexterm audience="hidden">strleft() function</indexterm>
<b>Purpose:</b> Returns the leftmost characters of the string. Shorthand for a call to
<codeph>substr()</codeph> with 2 arguments.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="strright">
<dt>
<codeph>strright(string a, int num_chars)</codeph>
</dt>
<dd>
<indexterm audience="hidden">strright() function</indexterm>
<b>Purpose:</b> Returns the rightmost characters of the string. Shorthand for a call to
<codeph>substr()</codeph> with 2 arguments.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="substr">
<dt>
<codeph>substr(string a, int start [, int len]), <ph id="substring">substring(string a, int start [, int
len])</ph></codeph>
</dt>
<dd>
<indexterm audience="hidden">substr() function</indexterm>
<b>Purpose:</b> Returns the portion of the string starting at a specified point, optionally with a
specified maximum length. The characters in the string are indexed starting at 1.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="translate">
<dt>
<codeph>translate(string input, string from, string to)</codeph>
</dt>
<dd>
<indexterm audience="hidden">translate() function</indexterm>
<b>Purpose:</b> Returns the input string with a set of characters replaced by another set of characters.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="trim">
<dt>
<codeph>trim(string a)</codeph>
</dt>
<dd>
<indexterm audience="hidden">trim() function</indexterm>
<b>Purpose:</b> Returns the input string with both leading and trailing spaces removed. The same as
passing the string through both <codeph>ltrim()</codeph> and <codeph>rtrim()</codeph>.
<p>
<b>Usage notes:</b> Often used during data cleansing operations during the ETL cycle, if input values might still have surrounding spaces.
For a more general-purpose function that can remove other leading and trailing characters besides spaces, see <codeph>btrim()</codeph>.
</p>
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
</dd>
</dlentry>
<dlentry id="upper">
<dt>
<codeph>upper(string a), <ph id="ucase">ucase(string a)</ph></codeph>
</dt>
<dd>
<indexterm audience="hidden">upper() function</indexterm>
<indexterm audience="hidden">ucase() function</indexterm>
<b>Purpose:</b> Returns the argument string converted to all-uppercase.
<p>
<b>Return type:</b> <codeph>string</codeph>
</p>
<p conref="../shared/impala_common.xml#common/usage_notes_blurb"/>
<p conref="../shared/impala_common.xml#common/case_insensitive_comparisons_tip"/>
</dd>
</dlentry>
</dl>
</conbody>
</concept>
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