UPDATE

Contents

• UPDATE

  • Syntax

  • EXPLAIN

  • Errors

Syntax

UPDATE <table_name>
SET <col> = <value> , ...
[ WHERE <expr> ]

If WHERE is not provided, all records will be updated.

The result (eg. UPDATE 8) contains the number of records actually updated. That is, more than this number of records may have matched, but only those that were changed will increment this counter.

EXPLAIN

The query planner will decide the best strategy to execute the UPDATE. You can see this plan by using the EXPLAIN prefix. See EXPLAIN.

Errors

Only one transaction is allowed to hold a modified version of a record at one time. This allows all other transactions to see the previous (frozen) version and the in-flight transaction to see it’s own version.

It’s not possible for multiple in-flight transactions to hold different versions of the same semantic row. This would break the serialization rules of the transaction since this would cause a conflict as to whos version is “correct”. This situation will return a SQLSTATE 40001 “serialization failure” error. Clients that receive this error should start the entire transaction again.