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我想从多个表中选择数据，并且我想从一个语句中的一列中获取总和。如果我只使用 sum (column)，我会将结果限制为一行，如果我使用 group by，sum (column) 似乎不起作用。或者我只是太愚蠢了。

也可能有一个更优雅的解决方案。（它在第 6 行的总和）。

SELECT 
    lb.date AS l_date, 
    gbb.id AS bid, 
    gbb.cash AS b_cash, 
    gpr.cash AS p_cash, 
    sum (gbb.cash) as t_cash,
    gbb.name
FROM 
    log_buildings lb, 
    game_building_basic gbb, 
    game_player_buildings gpb, 
    game_player_ress gpr
WHERE 
    lb.pid = :pid
    AND gpr.id = :pid
    AND gpb.pid = :pid
    AND lb.date >= gpr.date
    AND lb.bid = gbb.id
    AND gpb.buildings_id = gbb.id
    AND gpb.pid = :pid";
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1 回答 1

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首先，您应该学习查询的 JOIN 语法：

SELECT lb.date AS l_date, gbb.id AS bid, gbb.cash AS b_cash, gpr.cash AS p_cash,
       sum (gbb.cash) as t_cash, gbb.name
FROM log_buildings lb join
     game_building_basic gbb
     on lb.bid = bgg.bid join
     game_player_buildings gpb
     on gpb.buildings_id = gbb.id join
     game_player_ress gpr
     on lb.date >= gpr.date
WHERE lb.pid = :pid AND gpr.id = :pid AND gpb.pid = :pid AND gpb.pid = :pid"

如所写，此查询将返回所有字段的一组随机数据以及总和。通过使用汇总，您可以在单独的行中获取总计：

SELECT lb.date AS l_date, gbb.id AS bid, gbb.cash AS b_cash, gpr.cash AS p_cash,
       sum (gbb.cash) as t_cash, gbb.name
FROM log_buildings lb join
     game_building_basic gbb
     on lb.bid = bgg.bid join
     game_player_buildings gpb
     on gpb.buildings_id = gbb.id join
     game_player_ress gpr
     on lb.date >= gpr.date
WHERE lb.pid = :pid AND gpr.id = :pid AND gpb.pid = :pid AND gpb.pid = :pid"
group by lb.date, gbb.id, gbb.cash, gpr.cash, gbb.name with rollup

但是，您希望它作为单独的列，而不是单独的行（并rollup在不同级别产生多个总和。为此，您需要一个子查询：

SELECT lb.date AS l_date, gbb.id AS bid, gbb.cash AS b_cash, gpr.cash AS p_cash,
       gbb.name,
       (select sum(gbb.cash)
        FROM log_buildings lb join
             game_building_basic gbb
             on lb.bid = bgg.bid join
             game_player_buildings gpb
             on gpb.buildings_id = gbb.id join
             game_player_ress gpr
             on lb.date >= gpr.date
        WHERE lb.pid = :pid AND gpr.id = :pid AND gpb.pid = :pid AND gpb.pid = :pid
       ) as t_cash
FROM log_buildings lb join
     game_building_basic gbb
     on lb.bid = bgg.bid join
     game_player_buildings gpb
     on gpb.buildings_id = gbb.id join
     game_player_ress gpr
     on lb.date >= gpr.date
WHERE lb.pid = :pid AND gpr.id = :pid AND gpb.pid = :pid AND gpb.pid = :pid

在几乎任何其他数据库中，您都可以使用 windows 函数执行此操作：

SELECT lb.date AS l_date, gbb.id AS bid, gbb.cash AS b_cash, gpr.cash AS p_cash,
       gbb.name,sum(gbb.cash) over ()

但是 MySQL 不支持这种语法。

于 2012-09-29T21:02:32.490 回答