uses this isolation level, a <command>SELECT</command> query

(without a <literal>FOR UPDATE/SHARE</literal> clause) sees only data

committed before the query began; it never sees either uncommitted

data or changes committedduring query execution by concurrent

transactions. In effect, a <command>SELECT</command> query sees

data or changes committedby concurrent transactions during the query's

execution. In effect, a <command>SELECT</command> query sees

a snapshot of the database as of the instant the query begins to

run. However, <command>SELECT</command> does see the effects

of previous updates executed within its own transaction, even

<para>

The <firstterm>Repeatable Read</firstterm> isolation level only sees

data committed before the transaction began; it never sees either

uncommitted data or changes committedduring transaction execution

by concurrent transactions. (However,the query does see the

uncommitted data or changes committedby concurrent transactions during

the transaction's execution. (However,each query does see the

effects of previous updates executed within its own transaction,

even though they are not yet committed.) This is a stronger

guarantee than is required by the <acronym>SQL</acronym> standard