程序媛計劃——mysql索引
阿新 • • 發佈：2017-09-09
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定義：
索引是一種單獨的、物理的對數據庫表中一列或多列的值進行排序的一種存儲結構
#為字段創建索引
#在表中的字段中創建索引
mysql> create index ind_score on score(name); Query OK, 0 rows affected (0.03 sec) Records: 0 Duplicates: 0 Warnings: 0 #查看索引 mysql> show index from score; +-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | +-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+| score | 0 | PRIMARY | 1 | id | A | 4 | NULL | NULL | | BTREE | | | | score | 1 | ind_score | 1 | name | A | 4 | NULL | NULL | | BTREE | | |+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+ 2 rows in set (0.00 sec)
#也可以在創建表的時候創建索引
#刪除索引
mysql> drop index ind_score on score; Query OK, 0 rows affected (0.01 sec) Records: 0 Duplicates: 0 Warnings: 0
#用alter創建／刪除索引
mysql> alter table score add index ind_score(name); Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> alter table score drop index ind_score; Query OK, 0 rows affected (0.01 sec) Records: 0 Duplicates: 0 Warnings: 0
#創建索引值唯一的索引（好處是數據很多時能通過唯一索引快速查詢到數據）
mysql> create unique index uni_index on score(score); Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0
程序媛計劃——mysql索引