从数据库表的多行中放置案例条件以在 SQL 服务器中找到正确值的有效方法

Question

我几乎不需要任何帮助来简单地处理具有不同值的多个不同行的数据。

我需要根据不同的值应用CASE条件以提取正确的单个数据集行。

样本核心表名： Employee

ID EmployeeCode DEPT_Code
--------------------------
1  123          X
1  123          X1
1  123          X2

在DEPT_code ，我想应用CASE条件在一行中生成 output

• 如果多个Dept_code中的至少一个具有“X”，则value = 'ABC'
• 如果多个Dept_code有 'X1' 和 'X2'，则value = 'ABC'
• 如果多个Dept_code只有 'X1'，则value = 'xyz'
• 如果多个Dept_code只有 'X2'，则value = 'opq'

output 将在单行中。

 ID   EmployeeCode   Dept_Code
 ----------------------------------------------------
 1     123           (Value based on a CASE expression)

Answer 1

我会这样做：

未经测试

select e.ID, e.EmployeeCode
   -- each of C1, C2, C3 DEPT_Code will be null if the condition is not met.
   -- nested isnull statements select whichever condition is met first.
   ,isnull(max(C1.DEPT_Code), isnull(max(C2.DEPT_Code), isnull(max(C3.DEPT_Code), 'unknown'))) DEPT_Code
from Employee e
left outer join (  -- IDs that match your first or second condition, which are the same.
   select e1.ID, 'ABC' Dept_Code
   from Employee e1
   where DEPT_Code = 'X'
   group by e1.ID
) C1 on C1.ID = e.ID
left outer join ( -- IDs that match your third condition
   select e2.ID, 'xyz' Dept_Code
   from Employee e2
   group by e2.ID
   having min(e2.Dept_Code) = 'X1'
      and max(e2.Dept_Code) = 'X1'
) C2 on C2.ID = e.ID
left outer join ( -- IDs that match your fourth condition
   select e3.ID, 'opq' Dept_Code
   from Employee e3
   group by e3.ID
   having min(e3.Dept_Code) = 'X2'
      and max(e3.Dept_Code) = 'X2'
) C3 on C3.ID = e.ID
group by e.ID, e.EmployeeCode
order by e.ID

Answer 2

select ID, EmployeeCode,
    case
        when max(Dept_Code) = 'x2' then 3
        when max(Dept_Code) = 'x1' and count(*) = 1 then 2
        when max(Dept_Code) = 'x1' and min(Dept_Code) = 'x' then 1
        else 0
    end
from employee
group by ID, EmployeeCode

有各种各样的变化可以得到相同的结果。 由于您没有解释不同组合的含义，因此您必须根据数据决定如何设置逻辑。