null 不是数字,是空值,不能进行数学计算,因此不能用=号
select ename,comm from emp where comm is not null;
select ename,comm from emp where comm=0;
21、动力节点_MySQL_021_条件查询_like 模糊查询
select ename from emp where ename like ‘%s%’;
select ename from emp where ename like ‘s%’;
select ename from emp where ename like ‘_d%’;
select ename from emp where ename like ‘%n_’;