如何在Mysql数据库表中识别复合主键？

Question

如何在Mysql数据库表中识别复合主键？或

编辑2应该使用什么sql查询来显示包含复合主键的表的索引？

我在mysql数据库中有许多表，它们的复合键为2或3个主键，我使用phpmyadmin，我必须编写php脚本来识别哪个表有复合键，现在我可以使用查询来识别表的主键。

SHOW INDEXES FROM `".$row3['TABLE_NAME']."` WHERE Key_name = 'PRIMARY'

这给了我我想要的东西，但是现在我怎样才能找到我有复合键的索引呢？

编辑1

在Daniel上下文中的注释用于phpmyadmin中复合主键的外观

复合主键在phpmyadmin中如下所示：

Answer 1

更新：

对于更新的问题，您可能希望在PHP脚本中使用以下内容：

SELECT COUNT(*) num_keys 
FROM   information_schema.KEY_COLUMN_USAGE     
WHERE  table_name ='tb' AND constraint_name = 'PRIMARY';

如果表num_keys具有复合主键，则此查询将返回tb >1。

我不确定我是否理解您正在尝试实现的目标，但您可能需要考虑使用SHOW INDEX，如下所示：

CREATE TABLE tb (a int, b int, c int);
Query OK, 0 rows affected (0.21 sec)

ALTER TABLE tb ADD CONSTRAINT pk_tb PRIMARY KEY (a, b);
Query OK, 0 rows affected (0.06 sec)

SHOW INDEX FROM tb WHERE key_name='PRIMARY';
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| tb    |          0 | PRIMARY  |            1 | a           | A         |        NULL |     NULL | NULL   |      | BTREE      |         |
| tb    |          0 | PRIMARY  |            2 | b           | A         |           0 |     NULL | NULL   |      | BTREE      |         |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
2 rows in set (0.02 sec)

如果它不是复合键，那么您将只能在SHOW INDEX查询中得到一行：

CREATE TABLE tb2 (a int, b int, c int);
Query OK, 0 rows affected (0.05 sec)

ALTER TABLE tb2 ADD CONSTRAINT pk_tb PRIMARY KEY (a);
Query OK, 0 rows affected (0.05 sec)

SHOW INDEX FROM tb2 WHERE key_name='PRIMARY';
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| tb2   |          0 | PRIMARY  |            1 | a           | A         |           0 |     NULL | NULL   |      | BTREE      |         |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
1 row in set (0.02 sec)

Answer 2

SELECT COUNT( *  ) num_keys
FROM information_schema.KEY_COLUMN_USAGE
WHERE table_name = 'jos_modules_menu'
AND constraint_name = 'PRIMARY'
AND table_schema = 'pranav_test'

谢谢Daniel和Pranav :)