在WHERE CLAUSE中需要多个字符串条件

Question

SELECT stu.First_Name, stu.Last_Name, stu.Phone
FROM Student stu
JOIN Enrollment e
ON stu.Student_Id = e.Student_Id
JOIN Section sec
ON e.Section_Id = sec.Section_Id
JOIN Course c
ON sec.Course_No = c.Course_No
WHERE c.Description = 'Systems Analysis' AND c.Description = 'Project Managment'

嘿所有，希望是今天的最后一个问题（我很抱歉）。我想知道是否有办法检查多个字符串条件（是AND，而不是OR）。当我只使用一个我的联接工作正常，但我似乎无法使用两者。我的教科书希望我只使用课程的字符串关键字来解决它。

Answer 1

使用OR并仅过滤具有相同实例数的行到WHERE子句中指定的过滤器数。

SELECT  stu.First_Name, 
        stu.Last_Name, 
        stu.Phone
FROM    Student stu
        JOIN Enrollment e
            ON stu.Student_Id = e.Student_Id
        JOIN Section sec
            ON e.Section_Id = sec.Section_Id
        JOIN Course c
            ON sec.Course_No = c.Course_No
WHERE   c.Description IN ('Systems Analysis', 'Project Managment') -- two values
GROUP   BY stu.First_Name, stu.Last_Name, stu.Phone
HAVING  COUNT(*)  = 2 -- rows must have 2 instances