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Author Topic: MySQL and LIMIT for speed  (Read 2449 times)


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MySQL and LIMIT for speed
« on: January 23, 2010, 01:31:10 PM »
Does anyone know if an SQL query is speeded up when there is known to be only one row for a column even when the column is UNIQUE.
SELECT * FROM devices WHERE name='OpenWrt' LIMIT 1;
SELECT * FROM devices WHERE name='OpenWrt';
(name is UNIQUE)

MySQL could be intelligent enough to think that if a column is UNIQUE, it doesn't need to search for more rows and just return the first row.
On the other hand, it may not be ...

... and on the third hand, MySQL is soon Oracle.
Maybe I shouldn't presume MySQL and say from first principles that a LIMIT 1 will allways return on first match regardless of the SQL engine used.
(Gotta do a POC on using another SQL engine: it's a long time since this was "allowed", but no one did it. DBD::CSV - DBI driver for CSV files could be a "nice" easy proof giving txt for those who need it, and if it works there it'll work anywhere and postreq was once asked for ...).

MySQL fork: AskMonty
Google: Oracle and MySQL: good or bad ...
« Last Edit: January 23, 2010, 02:36:24 PM by oxo »