从数据库表上的多行放入大小写条件以在SQL Server中找到正确值的有效方法

Question

嗨，我几乎不需要帮助来简单地将具有多个distinct行且具有不同值的数据。我需要基于不同的值应用CASE条件，以便提取正确的单个数据集行。

样本核心表'Employee'

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

在DEPT_code上，我想应用CASE条件以在一行中产生输出

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

输出将在单行中。

**ID   EmployeeCode   Dept_Code**
 1     123            __*Case condition value*__

Answer 1

我会这样：

unested

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