在 SQL 中涉及不同比较运算符的 JOIN 子句中组合 CASE 语句

Question

我有两个 SELECT 语句，并希望根据输入参数将它们组合成一个 JOIN 语句：@UseFirstOne = true。 如果 @UseFirstOne 为 true，则我们在第一个条件下加入，如果为 false，则我们在第二个条件下加入。

1.

    JOIN X.[Employee] emp 
     ON emp.EmployeeId = @EmployeeId
     AND emp.BirthYear = @BirthYearFromParam

    JOIN X.[Employee] emp 
     ON emp.EmployeeId = @EmployeeId
     AND emp.BirthYear < @CurrentYear OR (emp.BirthYear = @CurrentYear AND emp.BirthMonth < @CurrentMonth)

如何将它们组合成一个 JOIN 语句？

Answer 1

AND ((
@UseFirstOne = 1 AND emp.BirthYear = @BirthYearFromParam)
OR (
@UseFirstOne =0 AND (emp.BirthYear < @CurrentYear OR (emp.BirthYear = @CurrentYear AND emp.BirthMonth < @CurrentMonth)
))