Difference between Row level and Statement level triggers - GeeksforGeeks (2024)

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Difference between Row level and Statement level triggers - GeeksforGeeks? ›

Row level triggers executes once for each and every row in the transaction. Statement level triggers executes only once for each single transaction. Specifically used for data auditing purpose. Used for enforcing all additional security on the transactions performed on the table.

Statement versus row triggers

A statement trigger fires once per triggering event and regardless of whether any rows are modified by the insert, update, or delete event. A row trigger fires once for each row affected by the triggering event. If no rows are affected, the trigger does not fire.

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.

With a per-row trigger, the trigger function is invoked once for each row that is affected by the statement that fired the trigger. In contrast, a per-statement trigger is invoked only once when an appropriate statement is executed, regardless of the number of rows affected by that statement.

Example: If 1500 rows are to be inserted into a table, the row level trigger would execute 1500 times. Example: If 1500 rows are to be inserted into a table, the statement level trigger would execute only once.

Statement-level triggers in Oracle databases execute actions for each transaction, responding to various database events like DML and DDL statements, system events, and user interactions. They act as programmed responses to specific table events, enhancing database management and automation.

To declare a trigger as a statement-level trigger, you can either use a FOR EACH STATEMENT clause or omit the FOR EACH clause. For clarity, it is recommended that you enter the FOR EACH STATEMENT clause if declaring a statement-level trigger.

When you define a trigger, you can specify the number of times the trigger action is to be run: Once for every row affected by the triggering statement, such as a trigger fired by an UPDATE statement that updates many rows. Once for the triggering statement, no matter how many rows it affects.

There is no official limit on the number of rows in a table, it is virtually unlimited.

What is the difference between return query and return next? ›

RETURN NEXT can be used with both scalar and composite data types; with a composite result type, an entire “table” of results will be returned. RETURN QUERY appends the results of executing a query to the function's result set.

Using COUNT function

Here's an example of COUNT function to find the number of rows in a table: SELECT COUNT(*) FROM your_table_name; Use your own table name in-place of your_table_name . Make sure that you are connected to your Postgres server via terminal before executing this command.

The FOR EACH ROW option determines whether the trigger is a row trigger or a statement trigger. If you specify FOR EACH ROW , then the trigger fires once for each row of the table that is affected by the triggering statement. These triggers are referred to as row-level triggers.

A table can have a maximum of three triggers: one update trigger, one insert trigger, and one delete trigger. Each trigger can apply to only one table. However, a single trigger can apply to all three user actions: update, insert, and delete.

Maximum Trigger Size

The size of a trigger cannot be more than 32K.

CLS allows for specific users to access only certain columns of a table relevant to their department, protecting sensitive data. RLS, on the other hand, restricts users to accessing only data rows pertinent to their role or department.

Row-level locking has the advantage of minimizing lock contention and maximizing concurrency, as it allows more transactions to access the same table simultaneously. However, row-level locking also has some drawbacks, such as higher overhead, larger lock lists, and potential deadlock situations.