Warum werden in diesem EXPLAIN keine Schlüssel verwendet?
Ich hatte erwartet, dass diese Abfrage einen Schlüssel verwendet.
mysql> DESCRIBE TABLE Foo;
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | bigint(20) | NO | PRI | NULL | auto_increment |
| name | varchar(50) | NO | UNI | NULL | |
+-------+-------------+------+-----+---------+----------------+
mysql> EXPLAIN SELECT id FROM Foo WHERE name='foo';
+----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+
| 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Impossible WHERE noticed after reading const tables |
+----+-------------+-------+------+---------------+------+---------+------+------+-----------------------------------------------------+
Foo hat einen eindeutigen Index fürname
, warum wird der Index nicht im @ verwendeSELECT
?