直接加法(1 + 1)与聚合函数SUM(1 + 1)有什么区别

Question

请参阅下面的查询，其中我通过直接添加而不使用函数来获取声誉值。

SELECT
    "User"."id",
    "User"."name",
    "User"."title",
    "User"."about",
    "User"."location",
    "User"."isModerator",
    "User"."createdAt",
    (
--      question vote
        COALESCE(SUM("PostVote"."value" * 10) FILTER (WHERE "value" = 1 AND "Post"."questionId" IS NULL), 0)::int 
        +
        COALESCE(SUM("PostVote"."value" * 2) FILTER (WHERE "value" = -1 AND "Post"."questionId" IS NULL), 0)::int 
        +
--      answer vote
        COALESCE(SUM("PostVote"."value" * 10) FILTER (WHERE "value" = 1 AND "Post"."questionId" IS NOT NULL AND "PostVote"."createdAt" > '2023-12-23'), 0)::int 
        +
        COALESCE(SUM("PostVote"."value" * 2) FILTER (WHERE "value" = -1 AND "Post"."questionId" IS NOT NULL), 0)::int 
        +
--      accepted answer
        (COALESCE(COUNT("answer"."id"), 0)::int * 15)
    ) as reputation
FROM "User"
LEFT JOIN "Post" ON "Post"."authorId" = "User"."id"
LEFT JOIN "PostVote" ON "PostVote"."postId" = "Post"."id"
LEFT JOIN "Post" as answer ON "Post"."acceptedAnswerId" = "answer"."id"
GROUP BY "User"."id"
ORDER BY reputation DESC, id

我这样做是因为SUM不能嵌套，我本来想做这样的事情。

-- ...
    SUM(
--      question vote
        COALESCE(SUM("PostVote"."value" * 10) FILTER (WHERE "value" = 1 AND "Post"."questionId" IS NULL), 0)::int 
        +
        COALESCE(SUM("PostVote"."value" * 2) FILTER (WHERE "value" = -1 AND "Post"."questionId" IS NULL), 0)::int 
        +
--      answer vote
        COALESCE(SUM("PostVote"."value" * 10) FILTER (WHERE "value" = 1 AND "Post"."questionId" IS NOT NULL AND "PostVote"."createdAt" > '2023-12-23'), 0)::int 
        +
        COALESCE(SUM("PostVote"."value" * 2) FILTER (WHERE "value" = -1 AND "Post"."questionId" IS NOT NULL), 0)::int 
        +
--      accepted answer
        (COALESCE(COUNT("answer"."id"), 0)::int * 15)
    ) as reputation
-- ...

我很好奇是否存在任何可能导致错误值的性能影响或求和？我已经用负值进行了测试，效果很好，也许我错过了一些东西。

我可以通过嵌套查询来使用 SUM 函数，但我认为这太冗长了。

Answer 1

区别在于 SUM 是一个聚合函数 - 它的参数是单个表达式，针对每个相关行进行计算，并给出所有结果的总和（如果没有结果则为 NULL） - 而

+

是一个普通的二元运算符：它出现在表达式内部，它的操作数是两个子表达式，对于任何给定的行，它给出两个子表达式给出的总和。

此外，它们处理 NULL 的方式有点不同；当任一子表达式给出 NULL 时，

+

给出 NULL，而 SUM 会跳过 NULL（并且仅当接收到 no 非 NULL 值时才返回 NULL）。

我认为讨论相对性能没有意义，因为它们的使用方式非常不同，因此在使用其中一种与另一种时不存在任何不同的查询。