mysql必知必會(4、檢索數據，5、排序檢索數據，6、過濾數據，7、數據過濾)

4、select語句

一、檢索單個列

select prod_name from products;

二、檢索多個列

select prod_name, prod_price from products;

三、檢索全部列

select * from products;

四、檢索不一樣的行

select distinct vend_id from products;（vend_id只返回不一樣的值）

五、限制結果

select prod_name from products limit 開始位置，檢索行數;

六、使用徹底限定的表名

select products.prod_name from products;

select products.prod_name from crashcourse.products;

5、排序檢索數據

一、根據prod_name排序

select prod_name from products order by prod_name;

二、按多個列排序

select prod_id, prod_price, prod_name from products order by prod_price, prod_name;

三、指定排序方向

select prod_id, prod_price, prod_name from products order by prod_price desc;(desc降序，asc升序)

select prod_id, prod_price, prod_name from products order by price_price desc, prod_name;

select prod_price from products order by prod_price desc limit 1;

6、過濾數據

一、使用where子句

select prod_name, prod_price from products where prod_price=2.50;

where支持

=，<>,!=,<,<=,>,>=,between

二、檢查單個值

select prod_name, prod_price from products where prod_name = 'fuses';

三、範圍檢查

select prod_name, prod_price from products where prod_price between 5 and 10;

四、空值檢查

select  prod_name from products where prod_price is null;

7、數據過濾

一、and操做符

select prod_id, prod_price, prod_name from products where vend_id = 1003 and prod_price <= 10;

二、or操做符

select prod_name, prod_price from product where vend_id = 1002 or vend_id = 1003;

三、計算次序

select prod_name, prod_price from products where vend_id = 1002 or vend_id = 1003 and prod_price >= 10;（先and在or）

select prod_name, prod_price from products where （vend_id = 1002 or vend_id = 1003 ）and prod_price >= 10

四、in操做符

select prod_name, prod_price from products where vend_id in (1002, 1003) order by prod_name;

五、not操做符

select prod_name, prod_price from products where vend_id not in (1002, 1003) order by prod_name;