What Cannot trigger in MySQL?
MySQL triggers cannot: Use SHOW , LOAD DATA , LOAD TABLE , BACKUP DATABASE, RESTORE , FLUSH and RETURN statements. Use statements that commit or rollback implicitly or explicitly such as COMMIT , ROLLBACK , START TRANSACTION , LOCK/UNLOCK TABLES , ALTER , CREATE , DROP , RENAME.
What are the triggers that can be used in MySQL tables?
There are 6 different types of triggers in MySQL:
- Before Update Trigger: As the name implies, it is a trigger which enacts before an update is invoked. …
- After Update Trigger: …
- Before Insert Trigger: …
- After Insert Trigger: …
- Before Delete Trigger: …
- After Delete Trigger:
Does trigger lock the table?
A trigger may reference multiple tables, and if a LOCK TABLES statement is used on one of the tables, other tables may at the same time also implicitly be locked due to the trigger. If the trigger writes to the other table, it will be write locked. …
Which of the following T SQL statements are not allowed in a DML trigger?
SQL Statements That Are Not Allowed in Triggers
alter table and alter database. truncate table. grant and revoke. update statistics.
What triggers MySQL?
A trigger in MySQL is a set of SQL statements that reside in a system catalog. It is a special type of stored procedure that is invoked automatically in response to an event. Each trigger is associated with a table, which is activated on any DML statement such as INSERT, UPDATE, or DELETE.
How do I trigger in Salesforce?
Get Started with Apex Triggers
- Write a trigger for a Salesforce object.
- Use trigger context variables.
- Call a class method from a trigger.
- Use the sObject addError() method in a trigger to restrict save operations.
Why MyISAM gives the best performance?
MyISAM is designed with the idea that your database is queried far more than its updated and as a result it performs very fast read operations. If your read to write(insert|update) ratio is less than 15% its better to use MyISAM.
What triggers SQL?
A SQL trigger is a database object which fires when an event occurs in a database. We can execute a SQL query that will “do something” in a database when a change occurs on a database table such as a record is inserted or updated or deleted. For example, a trigger can be set on a record insert in a database table.