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These are refugees from doc_prototype. They can be rendered with the DITA Open Toolkit version 2.3.3 by: /tmp/dita-ot-2.3.3/bin/dita \ -i impala.ditamap \ -f html5 \ -o $(mktemp -d) \ -filter impala_html.ditaval Change-Id: I8861e99adc446f659a04463ca78c79200669484f Reviewed-on: http://gerrit.cloudera.org:8080/5014 Reviewed-by: John Russell <jrussell@cloudera.com> Tested-by: John Russell <jrussell@cloudera.com>
117 lines
4.9 KiB
XML
117 lines
4.9 KiB
XML
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE concept PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="functions">
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<title>Overview of Impala Functions</title>
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<titlealts audience="PDF"><navtitle>Functions</navtitle></titlealts>
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<prolog>
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<metadata>
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<data name="Category" value="Impala"/>
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<data name="Category" value="Impala Functions"/>
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<data name="Category" value="SQL"/>
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<data name="Category" value="Data Analysts"/>
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<data name="Category" value="Developers"/>
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</metadata>
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</prolog>
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<conbody>
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<p>
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Functions let you apply arithmetic, string, or other computations and transformations to Impala data. You
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typically use them in <codeph>SELECT</codeph> lists and <codeph>WHERE</codeph> clauses to filter and format
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query results so that the result set is exactly what you want, with no further processing needed on the
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application side.
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</p>
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<p>
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Scalar functions return a single result for each input row. See <xref href="impala_functions.xml#builtins"/>.
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</p>
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<codeblock>[localhost:21000] > select name, population from country where continent = 'North America' order by population desc limit 4;
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[localhost:21000] > select upper(name), population from country where continent = 'North America' order by population desc limit 4;
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+-------------+------------+
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| upper(name) | population |
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+-------------+------------+
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| USA | 320000000 |
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| MEXICO | 122000000 |
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| CANADA | 25000000 |
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| GUATEMALA | 16000000 |
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+-------------+------------+
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</codeblock>
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<p>
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Aggregate functions combine the results from multiple rows:
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either a single result for the entire table, or a separate result for each group of rows.
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Aggregate functions are frequently used in combination with <codeph>GROUP BY</codeph>
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and <codeph>HAVING</codeph> clauses in the <codeph>SELECT</codeph> statement.
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See <xref href="impala_aggregate_functions.xml#aggregate_functions"/>.
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</p>
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<codeblock>[localhost:21000] > select continent, <b>sum(population)</b> as howmany from country <b>group by continent</b> order by howmany desc;
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+---------------+------------+
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| continent | howmany |
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+---------------+------------+
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| Asia | 4298723000 |
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| Africa | 1110635000 |
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| Europe | 742452000 |
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| North America | 565265000 |
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| South America | 406740000 |
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| Oceania | 38304000 |
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+---------------+------------+
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</codeblock>
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<p>
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User-defined functions (UDFs) let you code your own logic. They can be either scalar or aggregate functions.
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UDFs let you implement important business or scientific logic using high-performance code for Impala to automatically parallelize.
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You can also use UDFs to implement convenience functions to simplify reporting or porting SQL from other database systems.
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See <xref href="impala_udf.xml#udfs"/>.
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</p>
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<codeblock>[localhost:21000] > select <b>rot13('Hello world!')</b> as 'Weak obfuscation';
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+------------------+
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| weak obfuscation |
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+------------------+
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| Uryyb jbeyq! |
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+------------------+
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[localhost:21000] > select <b>likelihood_of_new_subatomic_particle(sensor1, sensor2, sensor3)</b> as probability
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> from experimental_results group by experiment;
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</codeblock>
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<p>
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Each function is associated with a specific database. For example, if you issue a <codeph>USE somedb</codeph>
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statement followed by <codeph>CREATE FUNCTION somefunc</codeph>, the new function is created in the
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<codeph>somedb</codeph> database, and you could refer to it through the fully qualified name
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<codeph>somedb.somefunc</codeph>. You could then issue another <codeph>USE</codeph> statement
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and create a function with the same name in a different database.
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</p>
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<p>
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Impala built-in functions are associated with a special database named <codeph>_impala_builtins</codeph>,
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which lets you refer to them from any database without qualifying the name.
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</p>
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<codeblock>[localhost:21000] > show databases;
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+-------------------------+
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| name |
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+-------------------------+
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| <b>_impala_builtins</b> |
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| analytic_functions |
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| avro_testing |
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| data_file_size |
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...
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[localhost:21000] > show functions in _impala_builtins like '*subs*';
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+-------------+-----------------------------------+
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| return type | signature |
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+-------------+-----------------------------------+
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| STRING | substr(STRING, BIGINT) |
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| STRING | substr(STRING, BIGINT, BIGINT) |
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| STRING | substring(STRING, BIGINT) |
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| STRING | substring(STRING, BIGINT, BIGINT) |
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+-------------+-----------------------------------+
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</codeblock>
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<p>
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<b>Related statements:</b> <xref href="impala_create_function.xml#create_function"/>,
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<xref href="impala_drop_function.xml#drop_function"/>
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</p>
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</conbody>
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</concept>
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