《mysql必知必会》学习_第七章_20180730_欢

Posted 2020-12-26 SUMIKO

第七章：数据过滤

P43

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

select prod_name,prod_price from products where vend_id=1002 or vend_id =1003; #检索的条件只要满足vend_id=1002 ,vend_id=1003即可#

P42

select prod_name,prod_price from products where vend_id =1002 or vend_id=1003 and prod_price >=10;#and和or同时存在的时候，优先处理and的操作符，理解为两个条件：（vend_id=1002) or（vend_id =1003 and prod_price) ,满足其一即可。

P42

select prod_name,prod_price from products where (vend_id =1002 or vend_id =1003 ) and prod_price>=10; #执行两个命令：(vend_id=1002,vend_id=1003)和prod_price>=10,圆括号（）的命令优先级高于and和or #

P43 in操作符 （in取合法值有逗号分开，如（5,8) )

select prod_name,prod_price from products where vend_id in (1002,1003) order by prod_name; #检索的条件vend_id 在1002到1003这个范围内#因为vend_id都是整数，所以上面的语句的结果和这个一样：

select prod_name,prod_price from products where vend_id=1002 or vend_id=1003 order by prod_name; 

但注意，in命令比or执行更快。

P45 

 select prod_name,prod_price from products where vend_id not in (1002,1003) order by prod_name; #not否定了not后面的条件,不检索(1002,1003) #