mysql - 限制左连接

Question

left 例如，我有以下查询并想限制表上的 left join，我该如何实现？

SELECT * FROM Base
LEFT JOIN Derived1 ON Base.id = Derived1.id
LEFT JOIN Derived2 ON Base.id = Derived2.id
LEFT JOIN Derived3 ON (Base.id = Derived3.id WHERE Derived3.name LIKE 'test%' LIMIT 5) <-----
WHERE Base.id = 'someid';

---

我想我可以这样写:

SELECT * FROM Base
LEFT JOIN Derived1 ON Base.id = Derived1.id
LEFT JOIN Derived2 ON Base.id = Derived2.id
LEFT JOIN Derived3 ON Base.id = (
    SELECT d3.id FROM Derived3 d3
    WHERE d3.name LIKE 'test%' AND Base.id = Derived3.id
    LIMIT 5
)
WHERE Base.id = 'someid';

但这给了我不正确的结果

我想要 Derived3 中的所有数据，但如果 Derived.name 等于 test 1，test 2，只有 5 个项目，测试 3 等 该表中可能有 100 000 000 个测试和几千个不以 'test' 开头的其他内容。

基本上，给我 Derived3 中的任何内容，最多 5 行以 'test' 开头。

我该如何解决？

Answer 1

检查下面的查询。

SELECT *
FROM Base
LEFT JOIN Derived1 ON Base.id = Derived1.id
LEFT JOIN Derived2 ON Base.id = Derived2.id
LEFT JOIN Derived3 ON (
        Base.id = Derived3.id
        AND Derived3.id IN (
            SELECT Derived3.id
            FROM Derived3
            WHERE Derived3.NAME LIKE 'test%' LIMIT 5
            )
        )
WHERE Base.id = 'someid'