是否有一種SQL語法會根據同一表中第3列的相等值搜索2列來創建新列？

Question

我有1個表，其字段名為：class_code，name1，class_code1，name2，class_code2。 我想搜索class_code的值，並將其顯示為class_code和僅名稱，其中class_code = class_code1或class_code = class_code2。 結果將顯示class_code和名稱

是否可以使用sql join語法？

這是表：

    class_code  name1     class_code1   name2     class_code2
    C0001       John      C0002         Ben       C0001
    C0002       Ren       C0001         Elizh     C0002
    C0001       Jeff      C0001         Harry     C0001

我需要的輸出是：

    class_code        name
    C0001             Ben
    C0002             Elizh
    C0001             Jeff
    C0001             Harry

Answer 1

如果打算將class_code1和name1放在一起，將class_code2和name2放在一起，則可以使用UNION ：

SELECT class_code1 AS class_code, name1 AS name FROM table
UNION
SELECT class_code2 AS class_code, name2 AS name FROM table

Answer 2

如果我做對了

SELECT class_code, name1 
FROM tbl
WHERE class_code = class_code1 
UNION --ALL
SELECT class_code, name2
FROM tbl
WHERE class_code = class_code2