我如何 select 多行使用多列而不使用多个子查询

Question

我有以下查询：

SELECT name, modelName, color, rarity, slot, power, chapter
FROM items
WHERE items.id = (SELECT head FROM characterdata WHERE steamid = ?)
OR items.id = (SELECT leftHand FROM characterdata WHERE steamid = ?)
OR items.id = (SELECT rightHand FROM characterdata WHERE steamid = ?)
OR items.id = (SELECT feet FROM characterdata WHERE steamid = ?);

它必须执行四次完全相同的查询，这似乎是不好的做法。 我如何重写它以便它只使用两个查询，也就是说它只需要获取一次字符数据？

Answer 1

您可以使用存在：

SELECT name, modelName, color, rarity, slot, power, chapter
FROM items i
WHERE EXISTS (SELECT 1
              FROM characterdata cd
              WHERE cd.steamid = ? AND
                    i.id IN (cd.head, cd.leftHand, cd.rightHand, cd.feet)
             );

这假设? 始终具有相同的值。

如果不是，您可以将其表达为：

SELECT name, modelName, color, rarity, slot, power, chapter
FROM items i
WHERE EXISTS (SELECT 1
              FROM characterdata cd
              WHERE (cd.steamid = ? AND i.id = cd.head) OR
                    (cd.steamid = ? AND i.id = cd.leftHand) OR
                    (cd.steamid = ? AND i.id = cd.rightHand) OR
                    (cd.steamid = ? AND i.id = cd.feet)
             );