|
On 09/16/2012 09:45 PM, Craig Ringer
wrote:
This seems under-documented and I haven't found much good info on it, so the best thing to do is test it. Found it, it's in the NOTES for CREATE TABLE. http://www.postgresql.org/docs/current/static/sql-createtable.html: When a UNIQUE or PRIMARY KEY constraint is not deferrable, PostgreSQL checks for uniqueness immediately whenever a row is inserted or modified. The SQL standard says that uniqueness should be enforced only at the end of the statement; this makes a difference when, for example, a single command updates multiple key values. To obtain standard-compliant behavior, declare the constraint as DEFERRABLE but not deferred (i.e., INITIALLY IMMEDIATE). Be aware that this can be significantly slower than immediate uniqueness checking. -- Craig Ringer |
