SQL 之 SELECT语句

1.展示所有列语法

select * from table; #table表示表名

示例：

select * from a

2.展示指定列语法

select column1, column2, ... from table;  #column1，column2列名

示例：

select subject, Score from a;

3.展示满足条件的数据(where)

select * from table where condition；  # condition  筛选条件
select column1,column2 from table where condition；  # condition  筛选条件

3.1  筛选条件：比较运算符，=、>、<、!=、>=、<=、<>

示例：

查询大于某个值的数据

select * from a WHERE Score >90

select No, subject from a WHERE Score > 90;

查询不等于某个值的数据

select * from a WHERE Score <>90；

select No, subject from a WHERE Score != 90;

　

3.2 筛选条件：between and

示例：

查询介于某个值之间的数据

select * from a WHERE Score BETWEEN 80 and 90;

3.3筛选条件：逻辑运算，and, or, not

示例：

查询小于某个或大于某个值的数据

select * from a WHERE Score<80 or Score>90;

3.4筛选条件：空值判断，is NULL 、is not NULL

示例：

查询不为空的数据

select * from a WHERE Score is not NULL;

3.5 筛选条件：模糊匹配， like

示例：

查询带有语的科目数据

select subject from a WHERE subject like "语%";  #以语开头的数据

select subject from a WHERE subject like "%语";   # 以语结尾的数据

select subject from a WHERE subject like "%语%";  # 含有语的数据

3.6筛选条件：存在与不存在，in、not in

示例：

查询不为数学、语文的数据

select * from a WHERE subject not in ("数学", "语文");

4.查询结果按某个字段升序、降序排序（order by）

语法：

select * from table order by column1 DESC;   #DESC 降序排序
select column1,column2,column3 from table where conditon order by column1 ASC； # 升序排序，不写默认升序

示例：

select * from a ORDER BY Score ASC;

select subject, Score from a  WHERE subject LIKE "%语%" ORDER  BY Score DESC;