是否有一种SQL语法会根据同一表中第3列的相等值搜索2列来创建新列？

Question

我有1个表，其字段名为：class_code，name1，class_code1，name2，class_code2。 我想搜索class_code的值，并将其显示为class_code和仅名称，其中class_code = class_code1或class_code = class_code2。 结果将显示class_code和名称

是否可以使用sql join语法？

这是表：

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

我需要的输出是：

    class_code        name
    C0001             Ben
    C0002             Elizh
    C0001             Jeff
    C0001             Harry

Answer 1

如果打算将class_code1和name1放在一起，将class_code2和name2放在一起，则可以使用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

如果我做对了

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