Question

具体问题是从类表中选择rollno，它出现在dbms中而不存在于数学中。

rollno sts sub
1      1    dbms
1      0    maths
2      1    dbms
2      0    maths
3      0    dbms
3      1    maths
4      0    dbms
4      0    maths
5      1    dbms
5      1    maths

Answer 1

您可以使用条件聚合：

select rollno
from mytable
group by rollno
having sum(sub = 'dbms' and sts = 1) > 0
   and sum(sub = 'maths' and sts = 1) = 0

这使用了以下事实：true计算结果为1，而在MySQL中，false计算结果为0。

sum(sub = 'dbms' and sts = 1)查找给定rollno的sub为dbms的行数，该值必须至少为1
sum(sub = 'maths' and sts = 1)查找sub为给定rollno的数学的行数，该值必须为0.

Demo

Answer 2

你可以使用两个带id的subselect而不是

select roolno
from my_table 
where sub in (select roolno from my_table  where sub ='dbms')
and sub not in (select roolno from my_table  where sub ='maths' )

MariaDB中的SQL如何使用2列中的数据从另一列中选择值？

2 个答案:

Demo