我们如何创建多列UNIQUE索引？

为了创建多列 UNIQUE 索引，我们需要在多个列上指定索引名称。以下示例将在“employee”表的“empid”、“first_name”、“last_name”列上创建名为“id_fname_lname”的多列索引 -

mysql> Create UNIQUE INDEX id_fname_lname on employee(empid,first_name,last_name); Query OK, 0 rows affected (0.41 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> describe employee; +------------+-------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+-------------+------+-----+---------+-------+ | empid | int(11) | YES | MUL | NULL | | | first_name | varchar(20) | YES | | NULL | | | last_name | varchar(20) | YES | | NULL | | +------------+-------------+------+-----+---------+-------+ 3 rows in set (0.12 sec)登录后复制

mysql> Show index from employeeG *************************** 1. row *************************** Table: employee Non_unique: 0 Key_name: id_fname_lname Seq_in_index: 1 Column_name: empid Collation: A Cardinality: 0 Sub_part: NULL Packed: NULL Null: YES Index_type: BTREE Comment: Index_comment: *************************** 2. row *************************** Table: employee Non_unique: 0 Key_name: id_fname_lname Seq_in_index: 2 Column_name: first_name Collation: A Cardinality: 0 Sub_part: NULL Packed: NULL Null: YES Index_type: BTREE Comment: Index_comment: *************************** 3. row *************************** Table: employee Non_unique: 0 Key_name: id_fname_lname Seq_in_index: 3 Column_name: last_name Collation: A Cardinality: 0 Sub_part: NULL Packed: NULL Null: YES Index_type: BTREE Comment: Index_comment: 3 rows in set (0.00 sec)登录后复制

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