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MySQL Tutorial - Violation of Unique Value Constraint

By: FYIcenter.com

(Continued from previous topic...)

What Happens If Unique Value Constraints Are Violated?

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:

mysql> INSERT INTO fyi_links (url) VALUES ('www.other.com');
ERROR 1062 (23000): Duplicate entry '0' for key 1

mysql> INSERT INTO fyi_links VALUES (101, 
  'sql.fyicenter.com', 
  NULL,
  0,
  '2006-04-30');
ERROR 1062 (23000): Duplicate entry '101' for key 1

(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?