主要是WHERE关键字的使用,对分组前的数据进行过滤
1、where子句操作符
以上有些操作是冗余的,注意并非DBMS都支持不同的写法,具体要看
2、检查单个值
1 select 2 col_name 3 from 4 table_name 5 where 6 col_name < num;
3、不匹配检查
1 select 2 col_name 3 from 4 table_name 5 where 6 col_name != 'str'
4、范围值检查
使用BETWEEN操作符
1 select 2 col_name 3 from 4 table_name 5 where 6 col_name 7 between num and num2;
5、空值检查
1 select 2 col_name 3 from 4 table_name 5 where 6 col_name 7 is null;
标签:name,数据,过滤,SQL,table,where,col,select From: https://www.cnblogs.com/shixiaogu/p/16744966.html