Example
Sometimes when tables are used mostly (or only) for reads, indexing does not help anymore and every little bit counts, one might use selects without LOCK to improve performance.
SQL Server
SELECT * FROM TableName WITH (nolock)
MySQL
SET SESSION TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
SELECT * FROM TableName;
SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;
Oracle
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
SELECT * FROM TableName;
DB2
SELECT * FROM TableName WITH UR;
where UR stands for "uncommitted read".
If used on table that has record modifications going on might have unpredictable results.
