select-for-update

SELECT FOR UPDATE is a SQL statement used to lock selected rows in a database table. When this statement is executed, the selected rows are locked and cannot be modified by other transactions until the lock is released. This is typically used in a transaction to ensure data consistency and prevent conflicts that could arise if multiple transactions attempt to modify the same data simultaneously.

Here is an example of how to use SELECT FOR UPDATE:

BEGIN TRANSACTION;

SELECT * FROM my_table WHERE id = 123 FOR UPDATE;

-- Perform some operations on the selected row(s) here

COMMIT;

In this example, the SELECT statement selects the row(s) from the table "my_table" where the id is equal to 123 and locks them for update. The transaction then performs some operations on the selected row(s) before committing the changes.

Note that SELECT FOR UPDATE only locks the selected rows, not the entire table. This means that other transactions can still read other rows in the table, but they cannot modify the locked rows until the lock is released.

It is important to use SELECT FOR UPDATE carefully and only when necessary, as it can potentially cause performance issues and block other transactions from accessing the locked rows.