Use Existing Column Values in the SET Clause in MySQL

Q

How To Use Existing Column Values in the SET Clause in MySQL?

✍: FYIcenter.com

A

If a row matches the WHERE clause in a UPDATE statement, existing values in this row can be used in expressions to provide new values in the SET clause. Existing values are represented by column names in the expressions. The tutorial exercise below shows a good example:

mysql> UPDATE fyi_links SET id = id+200, counts = id*2 
   WHERE id >= 500;
Query OK, 5 rows affected (0.01 sec)
Rows matched: 5  Changed: 5  Warnings: 0

mysql> SELECT id, url, notes, counts, DATE(created) 
   FROM fyi_links WHERE id >= 500;
+-----+-------------------+-------+--------+---------------+
| id  | url               | notes | counts | DATE(created) |
+-----+-------------------+-------+--------+---------------+
| 801 | moc.retneciyf.ved | Wrong |   1602 | 2006-04-30    |
| 802 | moc.retneciyf.abd | Wrong |   1604 | 2006-08-31    |
| 803 | moc.retneciyf.aqs | Wrong |   1606 | 2006-08-31    |
| 810 |                   | Wrong |   1620 | 2006-08-31    |
| 700 | moc.retneciyf.www | Wrong |   1400 | 2006-08-31    |
+-----+-------------------+-------+--------+---------------+
5 rows in set (0.00 sec)

This statement increased values in the id column by 200. It also updated the counts column with the newly increased id value.

⇒ Order of Columns in the SET Clause in MySQL

⇐ Update Column Values on Multiple Rows in MySQL

⇑ INSERT, UPDATE and DELETE Statements in MySQL

⇑⇑ MySQL Database Tutorials

2018-01-13, 3071🔥, 0💬

Omitting Columns in INSERT Statements in MySQL
How To Omit Columns with Default Values in INSERT Statement in MySQL? If you don't want to specify values for columns that have default values, or you want to specify values to columns in an order different than how they are defined, you can provide a column list in the INSERT statement. If a column... 2018-01-16, 4569🔥, 0💬

UPDATE with Subquery Returning No Rows in MySQL
What Happens If the UPDATE Subquery Returns No Rows in MySQL? If you use a subquery to assign new values in the SET clause in an UPDATE statement, and the subquery returns no rows for an outer row, MySQL will provide a NULL value to the SET clause. The tutorial exercise below shows you a good exampl... 2018-01-08, 4213🔥, 0💬

UPDATE Using Data from Other Tables in MySQL
How To Use Values from Other Tables in UPDATE Statements in MySQL? If you want to update values in one table with values from another table, you can use a subquery as an expression in the SET clause. The subquery should return only one row for each row in the update table that matches the WHERE clau... 2018-01-13, 3535🔥, 0💬

Use Existing Column Values in the SET Clause in MySQL
How To Use Existing Column Values in the SET Clause in MySQL? If a row matches the WHERE clause in a UPDATE statement, existing values in this row can be used in expressions to provide new values in the SET clause. Existing values are represented by column names in the expressions. The tutorial exer... 2018-01-13, 3072🔥, 0💬

Order of Columns in the SET Clause in MySQL
Is the Order of Columns in the SET Clause Important in MySQL? 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: Oracle provides you the existing values from the database on colu... 2018-01-13, 3067🔥, 0💬

Deleting an Existing Row from a Table in MySQL
How To Delete an Existing Row from a Table in MySQL? If you want to delete an existing row from a table, you can use the DELETE statement with a WHERE clause to identify that row. Here is good sample of DELETE statements: mysql> INSERT INTO fyi_links (url, id) VALUES ('www.myspace.com', 301);... 2018-01-08, 3061🔥, 0💬

Update Column Values on Multiple Rows in MySQL
How To Update Column Values on Multiple Rows in MySQL? If the WHERE clause in an UPDATE matches multiple rows, the SET clause will be applied to all matched rows. This rule allows you to update values on multiple rows in a single UPDATE statement. Here is a good example: mysql> UPDATE fyi_lin... 2018-01-13, 2996🔥, 0💬

Violation of Unique Value Constraint in MySQL
What Happens If Unique Value Constraints Are Violated in MySQL? If you are inserting a new record that has values violating a unique constraint, you will get an error. Note that primary key column has a unique value constraint by default. The following tutorial exercise gives you some good examples:... 2018-01-16, 2898🔥, 0💬

Updating Values in a Table in MySQL
How To Update Values in a Table in MySQL? If you want to update some values in one row or multiple rows in a table, you can use the UPDATE statement. The tutorial script below shows a good example: mysql> UPDATE fyi_links SET counts = 999, notes = 'Good.' WHERE id = 101; Query OK, 1 row affec... 2018-01-13, 2843🔥, 0💬

All rights in the contents of this web site are reserved by the individual author. fyicenter.com does not guarantee the truthfulness, accuracy, or reliability of any contents.