Hướng dẫn select for update mysql
15.7.2.4 Locking Reads If you query data and then insert or update related data within the same transaction, the regular
These clauses are primarily useful when dealing with tree-structured or graph-structured data, either in a single table or split across multiple tables. You traverse edges or tree branches from one place to another, while reserving the right to come back and change any of these “pointer” values. All
locks set by Note Locking reads are only possible when autocommit is disabled (either by beginning transaction with A locking read clause in an outer statement does not lock the rows of a table in a nested subquery unless a locking read clause is also specified in the subquery. For example, the following statement does not lock rows in table
To lock rows in table
Locking Read Examples Suppose that you want to insert a new row into a table First, use a consistent read to query the table To avoid this potential issue, perform the
After the For another example, consider an integer counter field in a table Here, To implement reading and incrementing the counter, first perform a locking read of the counter using
A
The preceding description is merely an example of how
The Locking Read Concurrency with NOWAIT and SKIP LOCKED If a row is locked by a transaction, a To avoid waiting for other transactions to release row locks,
Statements that use The following example demonstrates |