Collections:
Order of Columns in the SET Clause in MySQL
Is the Order of Columns in the SET Clause Important in MySQL?
✍: FYIcenter.com
Yes. The order of columns in the SET clause of the UPDATE statement is important. There is a BIG DIFFERENCE between MySQL and Oracle on update columns with previous values:
Tutorial exercise 1 - Setting "id" first and "counts" second:
mysql> SELECT id, url, notes, counts, DATE(created) FROM fyi_links WHERE url = 'dev.fyicenter.com'; +-----+-------------------+-------+--------+---------------+ | id | url | notes | counts | DATE(created) | +-----+-------------------+-------+--------+---------------+ | 101 | dev.fyicenter.com | Good. | 999 | 2006-04-30 | +-----+-------------------+-------+--------+---------------+ 1 row in set (0.00 sec) mysql> UPDATE fyi_links SET id = id+200, counts = id*2 WHERE url = 'dev.fyicenter.com'; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> SELECT id, url, notes, counts, DATE(created) FROM fyi_links WHERE url = 'dev.fyicenter.com'; +-----+-------------------+-------+--------+---------------+ | id | url | notes | counts | DATE(created) | +-----+-------------------+-------+--------+---------------+ | 301 | dev.fyicenter.com | Good. | 602 | 2006-04-30 | +-----+-------------------+-------+--------+---------------+ 1 row in set (0.00 sec) mysql> UPDATE fyi_links SET id = 101, counts = 999 WHERE url = 'dev.fyicenter.com'; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0
Notice that the "id" in the "counts" new value expression is taking the new value of the "id" column, because it appears before the "counts" columns in the SET clause.
Tutorial exercise 2 - Setting "counts" first and "id" second:
mysql> SELECT id, url, notes, counts, DATE(created) FROM fyi_links WHERE url = 'dev.fyicenter.com'; +-----+-------------------+-------+--------+---------------+ | id | url | notes | counts | DATE(created) | +-----+-------------------+-------+--------+---------------+ | 101 | dev.fyicenter.com | Good. | 999 | 2006-04-30 | +-----+-------------------+-------+--------+---------------+ 1 row in set (0.00 sec) mysql> UPDATE fyi_links SET counts = id*2, id = id+200 WHERE url = 'dev.fyicenter.com'; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0 mysql> SELECT id, url, notes, counts, DATE(created) FROM fyi_links WHERE url = 'dev.fyicenter.com'; +-----+-------------------+-------+--------+---------------+ | id | url | notes | counts | DATE(created) | +-----+-------------------+-------+--------+---------------+ | 301 | dev.fyicenter.com | Good. | 202 | 2006-04-30 | +-----+-------------------+-------+--------+---------------+ 1 row in set (0.00 sec) mysql> UPDATE fyi_links SET id = 101, counts = 999 WHERE url = 'dev.fyicenter.com'; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0
Notice that the "id" in the "counts" new value expression is taking the old value of the "id" column, because it appears after the "counts" columns in the SET clause.
⇒ UPDATE Using Data from Other Tables in MySQL
⇐ Use Existing Column Values in the SET Clause in MySQL
2018-01-13, 1525🔥, 0💬
Popular Posts:
What are binary literals supported in SQL Server Transact-SQL? Binary literals in Transact-SQL are s...
Is SQL Server Transact-SQL case sensitive? No. Transact-SQL is not case sensitive. Like the standard...
How To Format Time Zone in +/-hh:mm Format in SQL Server Transact-SQL? From the previous tutorial, y...
How To Break Query Output into Pages in MySQL? If you have a query that returns hundreds of rows, an...
How To Verify a User name with SQLCMD Tool in SQL Server? The quickest way to verify a user name in ...