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The default isolation level depends on the type of database to which
you're connected.  You can use C<SET ISOLATION TO level> to change the
isolation level.  If the database is unlogged, that is, it has no transaction
support, you can't set the isolation level.  In some more recent
versions, you can also set a transaction to C<READ ONLY>.
 
The default locking behaviour for reading and writing depends on the
isolation level, the way the table was defined, and on whether the
database was created with transactions enabled or not.
 
Rows returned by a SELECT statement can be locked to prevent them being
changed by another transaction, by appending C<FOR UPDATE> to the select
statement.  Optionally, you can specify a column list in parentheses
after the C<FOR UPDATE> clause.
 
The C<LOCK TABLE table_name IN lock_mode> statement can be used to
apply an explicit lock on a table. The lock mode can be C<SHARED> or
C<EXCLUSIVE>.  There are constraints on when tables can be unlocked,
and when locks can be applied.  Row/Page locking occurs with cursors
C<FOR UPDATE>.  In some types of database, some cursors are implicitly
created C<FOR UPDATE>.
 
 
=head1 SQL Dialect
 
=head2 Case Sensitivity of LIKE Operator
 
The LIKE operator is case sensitive.