7.1 单值索引

即一个索引只包含单个列，一个表可以有多个单列索引

7.2 唯一索引

索引列的值必须唯一，但允许有空值

7.3 主键索引

设定为主键后数据库会自动建立索引，innodb为聚簇索引

7.4 复合索引

即一个索引包含多个列

7.5 语法

# 查看索引
show index from table_name\G;

# 删除索引
drop index [indexName] on mytable;

# 随表一起创建
create table customer(
	...
	key(customer_name), # 单值索引
	unique(customer_name), # 唯一索引
    primary key(customer_name), # 主键索引
    key(customer_no,customer_name) # 复合索引
);

# 单独建索引
# 单值索引
create index idx_customer_name on customer(customer_name);

# 唯一索引
create unique index idx_customer_no on customer(customer_no);

# 主键索引
alter table customer add primary key customer(customer_no);

# 复合索引
create index idx_no_name on customer(customer_no,customer_name);
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