问题
Using MySQL, when I have a table with (for example) three keys (one primary, auto-increment, and two uniques on a column, eg. 'code' and 'name'), how can I (efficiently) know which uniqueness constraint was violated when doing an insert?
You get an error #1062 - Duplicate entry 'Value' for key 2, but how do I know key 2 is the key for the 'code' column and not the 'name' column?
We develop this application with multiple developers, and I want to prevent the day we don't add the constraints to a table in the same order, so the second key on my machine is the third key on another machine, and vice-versa.
Mapping to the exact column names involved is not really necessary, just to the key names is enough.
回答1:
As Bobby has suggested, SHOW indexes returns a resultset with relevant key index, check this page for further examples:
SHOW INDEXES FROM products_to_categories
WHERE Key_name = "PRIMARY"
AND Seq_in_index = '2';
+------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| products_to_categories | 0 | PRIMARY | 2 | category_id | A | 0 | NULL | NULL | | BTREE | |
+------------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
However this will probably require as much code if not more than the following workaround.
Check which value you inserted collides with an existing row in the table:
SELECT code FROM myTable WHERE code = 'the_value_you_tried_to_insert';
or
SELECT name FROM myTable WHERE name = 'the_value_you_tried_to_insert';
Albeit not a very elegant solution.
回答2:
Maybe this helps:
SHOW INDEX FROM arbeit
Bobby
来源：https://stackoverflow.com/questions/1486068/which-unique-key-is-hit-with-my-insert