[jira] [Created] (IGNITE-3698) ODBC: Support LEN(string) function.

["Vladimir Ozerov (JIRA)" <ji...@apache.org>]

Vladimir Ozerov created IGNITE-3698:
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             Summary: ODBC: Support LEN(string) function.
                 Key: IGNITE-3698
                 URL: https://issues.apache.org/jira/browse/IGNITE-3698
             Project: Ignite
          Issue Type: Task
          Components: odbc, SQL
    Affects Versions: 1.7
            Reporter: Vladimir Ozerov
            Assignee: Andrew Mashenkov
            Priority: Critical
             Fix For: 1.8


*Problem*
ODBC has standard function LEN(string). We do not support it at the moment because our H2 engine doesn't have this function. Instead, it has LENGTH function [1].
We need to support LEN as well.

*Solution*
It is necessary to investigate how we can add "LEN" support. Most probably we should implement custom H2 function [2] inside "core" module. It can be placed in the package {{org.apache.ignite.internal.processors.query.h2.ext.func}} in the module "ignite-indexing".
After that we should register it's alias inside the database, so that is LEN is correctly routed to that function.

There is a chance that we can skip implementation of the new function and directly route LEN alias to built-in LENGTH function. This is the most preferred solution (if achievable). See {{org.h2.expression.Function}} class in H2 JAR. It shows an example on how funcs are registered and mapped to SQL literals. E.g., this is how {{LENGTH}} is mapped:
{code}
addFunction("LENGTH", LENGTH, 1, Value.LONG);
{code}

Something semantically similar can be found in {{GridSqlFunction}} and {{GridSqlFunctionType}} classes in Ignite. 

Please also make sure that proper tests are added. 

[1] http://www.h2database.com/html/functions.html#length
[2] http://www.h2database.com/html/features.html#user_defined_functions



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