|Do you know where your variables are?|
Re^4: DBI, place holders and CGI forms (quote++)by tye (Sage)
|on Jun 02, 2011 at 18:25 UTC||Need Help??|
I never use quote myself.
Actually, quote() is the more general solution. I've run into quite a few different problems trying to use placeholders. And I've never noticed any performance problem with my failure to re-use prepared queries. I've actually had more problems due to people being too aggressive about trying to re-use prepared queries such as using prepare_cached() way too much.
A significant fraction (perhaps a majority) of the environments where I've done significant DBI work were such that placeholders had no performance impact at all. For example, the default with DBD::mysql seems to still be to not do server-side prepares.
At more than one recent employer I've experienced upgrading DBD::Pg such that prepares started happening server-side and then having to disable server-side prepares due to more than one resulting problem (the query planner got significantly stupider in a few important cases, it was incompatible with PgBouncer or other middle-layer tools, and other problems).
We had some breakage at PerlMonks because "limit ?" worked fine on older versions of DBD::mysql but then stopped working after some ugprade.
And I've had significant problems with placeholders when using DBD::ODBC. The first batch of problems were around certain data type checking such that "where somedate = '2011-01-01'" is no problem but "where somedate = ?" plus passing '2011-01-01' to execute() gave some "type mismatch" error.
The scariest problem was using DBD::ODBC and having "where somedate between cast(? as datetime) and cast(? as datetime)" work without emitting any errors or warnings but then returning the wrong data. But, of course:
worked exactly as expected (whether "cast( ... as datetime)" was included or not).
So, I like being able to use placeholders. But way too often that actually requires being able to disable server-side prepares which then just boils down to $dbh->quote() except that the DBD module is doing that call for you (and thus removes your claimed advantage).
Actually, the majority of my experience using DBI is via some wrapper (quite a few different ones, some extremely thin, some only moderately thin) that takes my column names and column values and assembles at least some of the SQL for me.