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MySQL Tutorial - UPDATE Using Data from Other Tables

By: FYIcenter.com

(Continued from previous topic...)

How To Use Values from Other Tables in UPDATE Statements?

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 clause. The tutorial exercise below shows you a good example:

mysql> CREATE TABLE fyi_rates (id INTEGER, 
   comment VARCHAR(16));
Query OK, 0 rows affected (0.53 sec)

mysql> INSERT INTO fyi_rates VALUES (101, 'The best');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO fyi_rates VALUES (102, 'Well done');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT INTO fyi_rates VALUES (103, 'Thumbs up');
Query OK, 1 row affected (0.00 sec)

mysql> UPDATE fyi_links SET notes = (
    SELECT comment FROM fyi_rates 
    WHERE fyi_rates.id = fyi_links.id
   )
   WHERE id > 0 AND id < 110;
Query OK, 3 rows affected (0.50 sec)
Rows matched: 3  Changed: 3  Warnings: 0

mysql> SELECT id, url, notes, counts FROM fyi_links 
   WHERE id > 0 AND id < 110;
+-----+-------------------+-----------+--------+
| id  | url               | notes     | counts |
+-----+-------------------+-----------+--------+
| 101 | dev.fyicenter.com | The best  |    999 |
| 102 | dba.fyicenter.com | Well done |      0 |
| 103 | sqa.fyicenter.com | Thumbs up |   NULL |
+-----+-------------------+-----------+--------+
3 rows in set (0.00 sec)

Note that if column names are confusing between the inner table and the outer table, you need to prefix column names with table names, like "fyi_rates.id = fyi_links.id".

(Continued on next topic...)

  1. What Are DML Statements?
  2. How To Create a Testing Table?
  3. How To Insert a New Row into a Table?
  4. How To Specify Default Values in INSERT Statement?
  5. How To Omit Columns with Default Values in INSERT Statement?
  6. What Happens If Unique Value Constraints Are Violated?
  7. How To Insert Multiple Rows with One INSERT Statement?
  8. How To Update Values in a Table?
  9. How To Update Column Values on Multiple Rows?
  10. How To Use Existing Column Values in the SET Clause?
  11. Is the Order of Columns in the SET Clause Important?
  12. How To Use Values from Other Tables in UPDATE Statements?
  13. What Happens If the UPDATE Subquery Returns No Rows?
  14. What Happens If the UPDATE Subquery Returns Multiple Rows?
  15. How To Delete an Existing Row from a Table?
  16. How To Delete Multiple Rows from a Table?
  17. How To Delete All Rows in a Table?

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