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https://issues.apache.org/jira/browse/DERBY-5466?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14638958#comment-14638958
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Scott Lewis commented on DERBY-5466:
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Yes, they would be invoked via SQL. For example
SELECT VAR_POP(value) FROM MYTABLE
where value is a column from MYTABLE. The above would return the population
variance of the value column. The function VAR_POP is create via this
statement (e.g.)
ij> CREATE DERBY AGGREGATE VAR_POP FOR DOUBLE RETURNS Double EXTERNAL NAME
'org.apache.derby.functions.VarPAggregator';
WRT package name...I'm fine with anything that works appropriately. There are
a number of built-in functions (not user defined) in
org.apache.derby.impl.sql.execute
which sort of implies that something like this might work for user-defined:
org.apache.derby.impl.sql.user.execute.statistics
but that might be too verbose for the Derby committers. Or
org.apache.derby.impl.sql.user.execute
What do you think?
> Add support for SQL Standard statistics functions, such as STDDEV_POP,
> STDDEV_SAMP, VAR_POP, VAR_SAMP
> -----------------------------------------------------------------------------------------------------
>
> Key: DERBY-5466
> URL: https://issues.apache.org/jira/browse/DERBY-5466
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Affects Versions: 10.8.1.2
> Reporter: Lukas Eder
> Priority: Minor
> Labels: derby_triage10_10
>
> Any of these RDBMS support the SQL standard statistics functions STDDEV_POP,
> STDDEV_SAMP, VAR_POP, VAR_SAMP:
> - DB2 (only STDDEV, VARIANE)
> - H2
> - HSQLDB
> - Ingres
> - MySQL
> - Oracle
> - Postgres
> - SQL Server (named STDEVP, STDEV, VARP, VAR)
> - Sybase ASE
> - Sybase SQL Anywhere
> These don't:
> - Derby
> - SQLite
> This would be a useful addition for Derby, I think.
> An even larger example list of possible statistics aggregate functions is
> listed in the Postgres documentation:
> http://www.postgresql.org/docs/9.0/static/functions-aggregate.html#FUNCTIONS-AGGREGATE-STATISTICS-TABLE
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