How instead of trigger works in SQL?
INSTEAD OF triggers cause their source DML operation to skip and they just execute the code provided inside them. Actual insert, delete or update operation do not occur at all. However they have their associated inserted and deleted tables simulating the DML operation.
What is the alternative for triggers?
One alternative you might want to look into are computed columns in SQL Server. If that matching is a pretty straightforward one (e.g. extract the character 10 through 14 from the string) or something like that, you could create a computed column to do so automagically – no trigger needed.
What is the purpose of instead of trigger?
An INSTEAD OF trigger is a trigger that allows you to update data in tables via their view which cannot be modified directly through DML statements. When you issue a DML statement such as INSERT , UPDATE , or DELETE to a non-updatable view, Oracle will issue an error.
What is difference between after trigger and instead of trigger?
AFTER trigger fires after a DML operation. INSTEAD OF trigger fires instead of a DML operation. Big difference. INSTEAD OF allows you to override functionality, or implement functionality that otherwise isn’t supported.
Can triggers be created on views?
Triggers may be created on views, as well as ordinary tables, by specifying INSTEAD OF in the CREATE TRIGGER statement. If one or more ON INSERT, ON DELETE or ON UPDATE triggers are defined on a view, then it is not an error to execute an INSERT, DELETE or UPDATE statement on the view, respectively.
Can we use after in SQL?
There is no difference between using FOR and AFTER.
Does trigger affect performance?
Yes, a table with a trigger will not perform as well as it would without it. Logic dictates that doing something is more expensive than doing nothing.
Why We Use After trigger in SQL?
An after trigger runs after the corresponding insert, update, or delete changes are applied to the table. The WHEN condition can be used in an SQL trigger to specify a condition. If the condition evaluates to true, the SQL statements in the SQL trigger routine body are run.
How can we specify a row level trigger?
Row-level trigger is identified by the FOR EACH ROW clause in the CREATE TRIGGER command. Statement-level triggers execute once for each transaction. For example, if a single transaction inserted 500 rows into the Customer table, then a statement-level trigger on that table would only be executed once.
Which statement is used to remove a trigger?
Which statement is used to remove a trigger? Explanation: In order to delete a trigger, the DROP TRIGGER statement is used. The DROP TRIGGER construct is used by writing the phrase ‘DROP TRIGGER’ followed by the scheme name specification.
What is after insert trigger?
An AFTER INSERT Trigger means that MySQL will fire this trigger after the INSERT operation is executed.
What do you mean by after in trigger?
After triggers: used to access field values that are set by the system (such as a record’s Id or LastModifiedDate field) and to effect changes in other records. The records that fire the after the trigger is read-only. We cannot use After trigger if we want to update a record because it causes a read-only error.