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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

Chapter 6: MySQL Language Reference 459 species which rows should be updated. Otherwise, all rows are updated. If the ORDER BY clause is specied, the rows will be updated in the order that is specied. If you specify the keyword LOW_PRIORITY, execution of the UPDATE is delayed until no other clients are reading from the table. If you specify the keyword IGNORE, the update statement will not abort even if we get duplicate key errors during the update. Rows that would cause con icts will not be updated. If you access a column from tbl_name in an expression, UPDATE uses the current value of the column. For example, the following statement sets the age column to one more than its current value: mysql> UPDATE persondata SET age=age+1; UPDATE assignments are evaluated from left to right. For example, the following statement doubles the age column, then increments it: mysql> UPDATE persondata SET age=age*2, age=age+1; If you set a column to the value it currently has, MySQL notices this and doesn't update it. UPDATE returns the number of rows that were actually changed. In MySQL Version 3.22 or later, the C API function mysql_info() returns the number of rows that were matched and updated and the number of warnings that occurred during the UPDATE. In MySQL Version 3.23, you can use LIMIT # to ensure that only a given number of rows are changed. 6.4.6 DELETE Syntax DELETE [LOW_PRIORITY | QUICK] FROM table_name [WHERE where_definition] [ORDER BY ...] [LIMIT rows] or DELETE [LOW_PRIORITY | QUICK] table_name[.*] [,table_name[.*] ...] FROM table-references [WHERE where_definition] or DELETE [LOW_PRIORITY | QUICK] FROM table_name[.*], [table_name[.*] ...] USING table-references [WHERE where_definition] DELETE deletes rows from table_name that satisfy the condition given by where_definition, and returns the number of records deleted. If you issue a DELETE with no WHERE clause, all rows are deleted. If you do this in AUTOCOMMIT mode, this works as TRUNCATE. See Section 6.4.7 [TRUNCATE], page 460. In MySQL 3.23, DELETE without a WHERE clause will return zero as the number of aected records.

MySQL Reference Manual

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