求一个简单的sql语句，关于多表join的

Question

有三个表如下：
table_link:

table_step:

table_test:

希望得到的结果：

其中table_link中的entity_id分别与table_step的step_id和table_test的test_id对应。最终结果就是需要找到table_link表中type为"test"和"step"的name并放到一起显示出来。

Answer 1

sql语句：

SELECT
    c.NAME,
    e.NAME type,
    e.entity_id 
FROM
    (
    SELECT
        b.NAME,
        b.entity_id 
    FROM
        ( SELECT NAME, step_id entity_id FROM table_step UNION SELECT NAME, test_id entity_id FROM table_test ) b 
    ) c,
    ( SELECT d.NAME, d.entity_id FROM ( SELECT type NAME, entity_id FROM table_link ) d ) e 
WHERE
    e.entity_id = c.entity_id;