Predicates for special uses

You can use certain special predicates to influence access path selection for a query.

For example, you can use the following special predicates:

WHERE (COL1=? OR 0=1)

The always-false OR 0=1 condition has the following effects on the compound predicate:

• Disables index access.
• Adds 0.04 to the estimated filter factor.
• Converts it to a non-Boolean predicate and disables certain query transformations, such as pushdown and transitive closure.

WHERE (COL1=? OR 0<>0)

The always-false OR 0<>0 condition has the following effects on the compound predicate:

• Disables index access.
• Adds 0.96 to the estimated filter factor, which indicates the predicate has low selectivity.
• Converts it to a non-Boolean predicate and disables certain query transformations, such as pushdown and transitive closure.

WHERE COL1=?+0

The +0 is removed when the query is transformed, however the predicate is marked as not matching indexable.

noncol-expr+0

noncol-expr-0

noncol-expr*1

noncol-expr/1

noncol-expr CONCAT blank-value

These predicates disable index access.