Since the query plan is done at prepare time, queries like this can cause a problem:
select * from foo
where bar = ?
and baz like ?

[download]
If there are two indexes, one on bar, and one on baz, which should be used? If baz is '%' (nothing but a wildcard), then it would be the wrong index to use, but if it's 'some long prefix%' then it's probably a good index to use, but there's no way to tell at prepare time. Trick: if you know baz is always the wrong index in this case but the database picks that index anyway (and your database does not support hints), you can fool it into not using the index (and hopefully using the correct one) by doing something like this (example also includes how to not use an index on a numeric column):
select * from foo
where bar = ?
and baz || '' like ?
and some_number + 0 = ?

[download]

In reply to Re: Re: Use Placeholders. For SECURITY and (sometimes) for PERFORMANCE by runrig
in thread Use Placeholders. For SECURITY and (sometimes) for PERFORMANCE by jZed

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