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ON UPDATE CASCADE: the best one usually: if you update a company_id in a row of table COMPANY the engine will update it accordingly on all USER rows referencing this COMPANY (but no triggers activated on USER table, warning). The engine will track the changes for you, it's good.
Derived tables and common table expressions can also be specified in multiple-table UPDATE and DELETE statements, but can only be used for reading data to specify rows to be updated or deleted. Generally, the view references must be updatable, meaning that they may be merged and not materialized. Composite views have more complex rules.
CHECK - Ensures that the values in a column satisfies a specific condition; DEFAULT - Sets a default value for a column if no value is specified; CREATE INDEX - Used to create and retrieve data from the database very quickly
CONDITION statement. To declare a handler, use the DECLARE ... HANDLER statement. See Section 15.6.7.1, “DECLARE ... CONDITION Statement”, and Section 15.6.7.2, “DECLARE ... HANDLER Statement”. For information about how the server chooses handlers when a condition occurs, see Section 15.6.7.6, “Scope Rules for Handlers”.
Introduction to MySQL UPDATE statement. The UPDATE statement updates data in a table. It allows you to change the values in one or more columns of a single row or multiple rows. The following illustrates the basic syntax of the UPDATE statement: UPDATE [LOW_PRIORITY] [IGNORE] table_name SET column_name1 = expr1, column_name2 = expr2, ... [WHERE ...
27 gru 2013 · You're confusing an update with a condition with a conditional update. For example the following is an update with a condition: UPDATE x SET y=IF(a=b, c, d) This is a conditional update: UPDATE x SET y=c WHERE a=b The first version is applied to all rows, the second to all matching rows. Use a WHERE clause to limit what rows your UPDATE is ...
21 sie 2024 · The IF-THEN statement in SQL is used to execute a block of code if a specified condition is true. If the condition evaluates to true, the code within the THEN block is executed. If the condition is false, the block is skipped. Syntax: IF condition THEN. statements; END IF; Parameters Used:
