A LIKE predicate with an escape-expression does not use an
available index when the match-expression is a GRAPHIC or
VARGRAPHIC column, and both the pattern-expression and
escape-expression are CHAR or VARCHAR type. For example:
... WHERE graphiccol LIKE 'abc!_%' ESCAPE '!'
Any index on column graphiccol will not be exploited possibly
resulting in poor query performance. This only applies to a
unicode database, since mixing of graphic and non-graphic types
is not allowed otherwise. |
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* USERS AFFECTED: *
* ALL *
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* PROBLEM DESCRIPTION: *
* Internally we treat LIKE just as any other function call, we *
* follow the function resolution rules to find the best fit *
* function. We have four (internal) versions of LIKE: *
* *
* LIKE(VC,VC) *
* LIKE(VC,VC,VC) *
* LIKE(VG,VG) *
* LIKE(VG,VG,VG) *
* *
* Following the documented function resolution rules, we map *
* these calls as follows: *
* *
* VG LIKE VC -> LIKE( VG, VARGRAPH(VC) ) best fit is *
* LIKE(VG,VG) *
* VG LIKE VC ESCAPE VC -> LIKE( VARCHAR(VG), VC, VC ) this is *
* the best fit as there is only one cast *
* *
* The behaviour makes sense if we think of LIKE as a function *
* call. This APAR will try to avoid a cast on the first *
* argument since that is the only argument that can reference *
* a column, and hence a cast will hide the column index. *
****************************************************************
* RECOMMENDATION: *
* Upgrade to DB2 Version 9.8 and Fix Pack 0 *
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