所有坚韧不拔的努力迟早会取得报酬的。 —— 安格尔
1.索引操作
（1）添加索引
| Plain Text alter table [table_name] add index [index_name]（column）; |
索引名可省略，省略时，会根据第一个索引列赋予名称
（2）删除索引
| Plain Text alter table [table_name] drop [index_name]; |
2.SQL drop
(1)删除数据表
(2)删除数据库
| Plain Text Drop database [database_name]; |
(3)清空数据表
该指令可以在保留数据表的情况下，清空数据表数据；
| Plain Text Truncate table [table_name]; |
(4)删除表字段
| Plain Text Alter table [table-name] drop[column]; |
| Plain Text Drop table [table_name]; |
3.SQL insert
(1)全字段插入
| Plain Text Insert into [table-name] ([column1],[column2]) values([val1],[val2]); |
全字段中col1,col2可省略
| Plain Text ?insert into user values('lkz',21); |
(2)显示表内容
为了对上述语句进行验证
Select *from [table_name]
（3）单字段插入
| Plain Text Insert into [table_name]([col1]) values(val1); |
(4)批量插入
| Plain Text Insert into [table_name] ([col1],[col2]) values([val1],[val2]),([val3],[val4]); |
4.SQL select
(1)select version(); 查看版本
(2)select current_user;查看当前用户
(3)查询数据表数据
| Plain Text Select [col1],[col2] from [table_name]; |
(4)查询表中所有字段
Select *from [table_name];
(5)查询表中单字段
| Plain Text Select [col1] from [table_name]; |
5.SQL distinct
Distinct用于返回不同的值，相当于去重的效果
(1)单字段查询
| Plain Text select distinct [col1] from [table_name]; |
（2）多字段查询
| Plain Text Select distinct [col1],[col2] from [table_name]; |
6.SQL where
(1)单条件查询
| Plain Text Select [col1] from [table_name] where [col2] [condition] [val]; |
condition为运算符
(2)多条件查询
后面条件可以根据需求来进行设定，可以使用多个and，也可以换成or
7.SQL null
(1)查找字段为空或非空
| Plain Text Select [col1] from [table_name] where [col2] is null; Select [col1] from [table_name] where [col2] is not null; |
8.SQL order by
(1)单字段排序
| Plain Text Select [col1],[col2] from [table_name] order by[col] [desc|asc]; |
排序默认为升序排序，也可自由选择，asc 为升序，desc为降序
(2)多字段排序
Select [col1],[col2] from [table_name] order by[col1] [desc|asc]，[col2] [desc|asc];
8.SQL update
(1)单字段更新
| Plain Text Update [table_name] set [col2]=[val] where [col1]=[val]; |
(2)多字段更新
9.SQL delete
| Plain Text Delete from [table_name] where [col]=[val]; |
若有多行相同数据，则会被同时删除
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