LEFT JOIN 删除行而不过滤原始 table

Question

以下查询让我感到困惑。它不显示 products table 中的所有行，如果我这样做 WHERE (inventory_to_pos.POSID IS NULL OR inventory_to_pos.POSID = ?) 并绑定可能存在或可能不存在的 POSID在 inventory_to_pos。当 LEFT JOIN-ing a table 时，当我只过滤原始 [=29] 时，我是否应该从原始 table 中获取 all 行=] 并在 LEFT JOIN 的 tables?

的任何条件下使用 IS NULL

SELECT products.ID,products.NAME,products.VOLUME,productcombinations.PRODUCTID,productcombinations.PART,inventory_to_pos.FULLCOUNT
FROM products
LEFT JOIN productcombinations ON products.ID = productcombinations.PARTOF
LEFT JOIN inventory_to_pos ON products.ID = inventory_to_pos.PRODUCT 
WHERE products.INVENTORY = 1
AND products.AVAILABLE = 1
AND products.ID > 0
AND (inventory_to_pos.POSID IS NULL OR inventory_to_pos.POSID = ?);

如果 inventory_to_pos.PRODUCT 和 inventory_to_pos.POSID 对于给定的产品和 POSID 不存在，则我没有任何行。为什么？

Answer 1

将所有相关的 invetory_to_pos 子句移动到 LEFT JOIN 中，即：

SELECT
    products.ID,
    products. NAME,
    products.VOLUME,
    productcombinations.PRODUCTID,
    productcombinations.PART,
    inventory_to_pos.FULLCOUNT
FROM
    products
LEFT JOIN productcombinations ON products.ID = productcombinations.PARTOF
LEFT JOIN inventory_to_pos ON products.ID = inventory_to_pos.PRODUCT AND (
    inventory_to_pos.POSID IS NULL
    OR inventory_to_pos.POSID = ?
)
WHERE
    products.INVENTORY = 1
AND products.AVAILABLE = 1
AND products.ID > 0

LEFT JOIN 删除行而不过滤原始 table

LEFT JOIN drops rows without filtering original table

mysql

left-join