impala/docs/topics/impala_varchar.xml

<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="varchar" rev="2.0.0">

  <title>VARCHAR Data Type (<keyword keyref="impala20"/> or higher only)</title>
  <titlealts audience="PDF"><navtitle>VARCHAR</navtitle></titlealts>
  <prolog>
    <metadata>
      <data name="Category" value="Impala"/>
      <data name="Category" value="Impala Data Types"/>
      <data name="Category" value="SQL"/>
      <data name="Category" value="Data Analysts"/>
      <data name="Category" value="Developers"/>
      <data name="Category" value="Schemas"/>
    </metadata>
  </prolog>

  <conbody>

    <p rev="2.0.0">
      <indexterm audience="hidden">VARCHAR data type</indexterm>
      A variable-length character type, truncated during processing if necessary to fit within the specified
      length.
    </p>

    <p conref="../shared/impala_common.xml#common/syntax_blurb"/>

    <p>
      In the column definition of a <codeph>CREATE TABLE</codeph> statement:
    </p>

<codeblock><varname>column_name</varname> VARCHAR(<varname>max_length</varname>)</codeblock>

    <p>
      The maximum length you can specify is 65,535.
    </p>

    <p conref="../shared/impala_common.xml#common/partitioning_bad"/>

<!--
<p>
This type can be used for partition key columns.
Because of the efficiency advantage of numeric values over character-based values,
if the partition key is a string representation of a number,
prefer to use an integer data type with sufficient range (<codeph>INT</codeph>,
<codeph>BIGINT</codeph>, and so on) rather than this type.
</p>
-->

    <p conref="../shared/impala_common.xml#common/hbase_no"/>

    <p conref="../shared/impala_common.xml#common/parquet_blurb"/>

    <ul>
      <li>
        This type can be read from and written to Parquet files.
      </li>

      <li>
        There is no requirement for a particular level of Parquet.
      </li>

      <li>
        Parquet files generated by Impala and containing this type can be freely interchanged with other components
        such as Hive and MapReduce.
      </li>

      <li>
        Parquet data files can contain values that are longer than allowed by the
        <codeph>VARCHAR(<varname>n</varname>)</codeph> length limit. Impala ignores any extra trailing characters
        when it processes those values during a query.
      </li>
    </ul>

    <p conref="../shared/impala_common.xml#common/text_blurb"/>

    <p>
      Text data files can contain values that are longer than allowed by the
      <codeph>VARCHAR(<varname>n</varname>)</codeph> length limit. Any extra trailing characters are ignored when
      Impala processes those values during a query.
    </p>

    <p><b>Avro considerations:</b></p>
    <p conref="../shared/impala_common.xml#common/avro_2gb_strings"/>

    <p conref="../shared/impala_common.xml#common/schema_evolution_blurb"/>

    <p>
      You can use <codeph>ALTER TABLE ... CHANGE</codeph> to switch column data types to and from
      <codeph>VARCHAR</codeph>. You can convert from <codeph>STRING</codeph> to
      <codeph>VARCHAR(<varname>n</varname>)</codeph>, or from <codeph>VARCHAR(<varname>n</varname>)</codeph> to
      <codeph>STRING</codeph>, or from <codeph>CHAR(<varname>n</varname>)</codeph> to
      <codeph>VARCHAR(<varname>n</varname>)</codeph>, or from <codeph>VARCHAR(<varname>n</varname>)</codeph> to
      <codeph>CHAR(<varname>n</varname>)</codeph>. When switching back and forth between <codeph>VARCHAR</codeph>
      and <codeph>CHAR</codeph>, you can also change the length value. This schema evolution works the same for
      tables using any file format. If a table contains values longer than the maximum length defined for a
      <codeph>VARCHAR</codeph> column, Impala does not return an error. Any extra trailing characters are ignored
      when Impala processes those values during a query.
    </p>

    <p conref="../shared/impala_common.xml#common/compatibility_blurb"/>

    <p>
      This type is available on CDH 5.2 or higher.
    </p>

    <p conref="../shared/impala_common.xml#common/internals_min_bytes"/>

    <p conref="../shared/impala_common.xml#common/added_in_20"/>

    <p conref="../shared/impala_common.xml#common/column_stats_variable"/>

    <p conref="../shared/impala_common.xml#common/restrictions_blurb"/>

    <p conref="../shared/impala_common.xml#common/blobs_are_strings"/>

    <p conref="../shared/impala_common.xml#common/example_blurb"/>

    <p>
      The following examples show how long and short <codeph>VARCHAR</codeph> values are treated. Values longer
      than the maximum specified length are truncated by <codeph>CAST()</codeph>, or when queried from existing
      data files. Values shorter than the maximum specified length are represented as the actual length of the
      value, with no extra padding as seen with <codeph>CHAR</codeph> values.
    </p>

<codeblock>create table varchar_1 (s varchar(1));
create table varchar_4 (s varchar(4));
create table varchar_20 (s varchar(20));

insert into varchar_1 values (cast('a' as varchar(1))), (cast('b' as varchar(1))), (cast('hello' as varchar(1))), (cast('world' as varchar(1)));
insert into varchar_4 values (cast('a' as varchar(4))), (cast('b' as varchar(4))), (cast('hello' as varchar(4))), (cast('world' as varchar(4)));
insert into varchar_20 values (cast('a' as varchar(20))), (cast('b' as varchar(20))), (cast('hello' as varchar(20))), (cast('world' as varchar(20)));

select * from varchar_1;
+---+
| s |
+---+
| a |
| b |
| h |
| w |
+---+
select * from varchar_4;
+------+
| s    |
+------+
| a    |
| b    |
| hell |
| worl |
+------+
[localhost:21000] &gt; select * from varchar_20;
+-------+
| s     |
+-------+
| a     |
| b     |
| hello |
| world |
+-------+
select concat('[',s,']') as s from varchar_20;
+---------+
| s       |
+---------+
| [a]     |
| [b]     |
| [hello] |
| [world] |
+---------+
</codeblock>

    <p>
      The following example shows how identical <codeph>VARCHAR</codeph> values compare as equal, even if the
      columns are defined with different maximum lengths. Both tables contain <codeph>'a'</codeph> and
      <codeph>'b'</codeph> values. The longer <codeph>'hello'</codeph> and <codeph>'world'</codeph> values from the
      <codeph>VARCHAR_20</codeph> table were truncated when inserted into the <codeph>VARCHAR_1</codeph> table.
    </p>

<codeblock>select s from varchar_1 join varchar_20 using (s);
+-------+
| s     |
+-------+
| a     |
| b     |
+-------+
</codeblock>

    <p>
      The following examples show how <codeph>VARCHAR</codeph> values are freely interchangeable with
      <codeph>STRING</codeph> values in contexts such as comparison operators and built-in functions:
    </p>

<codeblock>select length(cast('foo' as varchar(100))) as length;
+--------+
| length |
+--------+
| 3      |
+--------+
select cast('xyz' as varchar(5)) &gt; cast('abc' as varchar(10)) as greater;
+---------+
| greater |
+---------+
| true    |
+---------+
</codeblock>

    <p conref="../shared/impala_common.xml#common/udf_blurb_no"/>

    <p conref="../shared/impala_common.xml#common/related_info"/>

    <p>
      <xref href="impala_string.xml#string"/>, <xref href="impala_char.xml#char"/>,
      <xref href="impala_literals.xml#string_literals"/>,
      <xref href="impala_string_functions.xml#string_functions"/>
    </p>
  </conbody>
</concept>