Cheng Plan--mysql Index

Definition:An index is a single, physical storage structure that sorts the values of one or more columns in a database table#为字段创建索引

#在表中的字段中创建索引
Mysql> Create IndexInd_score onscore (name); Query OK,0Rows Affected (0.03sec) Records:0Duplicates:0Warnings:0#查看索引mysql>ShowIndex  fromscore;+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+ ------+------------+---------+---------------+| 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|         |               |+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+- -----+------------+---------+---------------+2Rowsinch Set(0.00Sec

#也可以在创建表的时候创建索引

#删除索引

MySQL>dropindexon0 rows affected (0.01  0  0  0

#用alter创建/Delete Index

Mysql> Alter TableScoreAdd IndexInd_score (name); Query OK,0Rows Affected (0.02sec) Records:0Duplicates:0Warnings:0MySQL> Alter TableScoreDrop IndexInd_score; Query OK,0Rows Affected (0.01sec) Records:0Duplicates:0Warnings:0

#创建索引值唯一的索引 (the benefit is that data can be quickly queried by a unique index when there is a large number)

MySQL>Createuniqueindexon0 rows affected (  0.020  0  0

Cheng Plan--mysql Index