Trigger updating column

Because of the behaviors described above, programmers are encouraged to prefer AFTER triggers over BEFORE triggers.

trigger updating column-21trigger updating column-18trigger updating column-12

Hence explicitly specifying FOR EACH ROW is optional.

FOR EACH ROW implies that the SQL statements specified in the trigger may be executed (depending on the WHEN clause) for each database row being inserted, updated or deleted by the statement causing the trigger to fire.

An ON CONFLICT clause may be specified as part of an UPDATE or INSERT action within the body of the trigger.

However if an ON CONFLICT clause is specified as part of the statement causing the trigger to fire, then conflict handling policy of the outer statement is used instead.

If no WHEN clause is supplied, the SQL statements are executed every time the trigger fires.

The BEFORE or AFTER keyword determines when the trigger actions will be executed relative to the insertion, modification or removal of the associated row.

Note that the sqlite3_changes() and sqlite3_total_changes() interfaces do not count INSTEAD OF trigger firings, but the count_changes pragma does count INSTEAD OF trigger firing.

Assuming that customer records are stored in the "customers" table, and that order records are stored in the "orders" table, the following UPDATE trigger ensures that all associated orders are redirected when a customer changes his or her address: CREATE TABLE customer( cust_id INTEGER PRIMARY KEY, cust_name TEXT, cust_addr TEXT ); CREATE VIEW customer_address AS SELECT cust_id, cust_addr FROM customer; CREATE TRIGGER cust_addr_chng INSTEAD OF UPDATE OF cust_addr ON customer_address BEGIN UPDATE customer SET cust_addr=NEW.cust_addr WHERE cust_id=NEW.cust_id; END; Causes the customer.cust_addr field to be updated for a specific customer entry that has customer.cust_id equal to the $cust_id parameter.

Such a trigger will only fire when changes are made to the target table by the application that defined the trigger.

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