Question

这应该是方案人员经常遇到的问题,但我从未尝试过这样做。

这就是我的解释。因此,我需要从表动物群中 values取价值:

 @"SELECT z.predator, z.prey FROM Zoo AS z WHERE z.preyType=@carnivore"

现在,我可以把所有价值观列入清单。我需要在一个电网中显示该电离层的详细情况。现在有 go子和z(为了时间目的,是为了ger、ie、各自的ids),我需要把有意义的价值观集中起来,向终端用户展示(我只能展示他们的ids)。因此,我现在可以这样做:

 foreach (Zoo z in lstZoo)
 {
       Animal predator = GetFromAnimalTable(z.Predator)
       Animal prey = GetFromAnimalTable(z.Prey)
 }

这将使方案进展缓慢。 Can 我问一看所有细节? 与此类似:

   SELECT (SELECT * FROM ANIMAL WHERE id=z.predator), 
          (SELECT * FROM ANIMAL WHERE id=z.prey) 
   FROM Zoo AS z WHERE z.preyType=@carnivore

如果我能把价值观读到一个新的大目标? 或者这是否被视为一种不良做法?

<><>UPDATE: 这样做是否是一种标准做法? 还是像我第一次说过的那样,建议个人居住?

<><>UPDATE 2 我似乎犯了一个可怕的错误,即不像我所需要的那样把问话说出来。我认为,为了达到我的要求,我可以 t笑这里的答案,而不必用括号构造查阅。

这里,我的实际问题是:

SELECT z.predator, p.lifeSpan, z.prey 
FROM Zoo AS z 
INNER JOIN Plants AS p ON p.parent_id=z.id 
WHERE z.preyType=@carnivore

实际上,我已经有一个INNER JOIN问询表。现在,我需要获得Z.predator(及其相应的动物表值)、p.lifeSpan、z.prey(及其相应的动物表值)的Z.predator(SlectT)值,以满足INNER JOIN和WHERE的条件。

一部假冒的法典就是这样:

SELECT (SELECT * FROM ANIMAL WHERE id=z.predator), p.lifeSpan, (SELECT * FROM ANIMAL WHERE id=z.prey) 
FROM Zoo AS z INNER JOIN Plants AS p ON p.parent_id=z.id 
WHERE z.preyType=@carnivore

It should be pretty easy to extend my requirement from the answers here, but no success till now. I tried:

SELECT a1.*, p.lifeSpan, a2.* 
FROM Zoo AS z 
INNER JOIN Plants AS p ON p.parent_id=z.id 
INNER JOIN Animal AS a1 ON (a1.id=z.predator)
INNER JOIN Animal AS a2 ON (a2.id=z.prey)
WHERE z.preyType=@carnivore

这里有许多带有方括号的备选案文。如何妥善安排上述询问?

Answer 1

It seems this your latest query attempt:

SELECT a1.*, p.lifeSpan, a2.* 
FROM Zoo AS z 
INNER JOIN Plants AS p ON p.parent_id=z.id 
INNER JOIN Animal AS a1 ON (a1.id=z.predator)
INNER JOIN Animal AS a2 ON (a2.id=z.prey)";
WHERE z.preyType=@carnivore

声明内抛弃半殖民地。并摒弃双重引用。

简单地简化了《平等法》,现在将《家庭平等法》条款排除在外。

然后,你应更有能力处理进入散射发动机需要多功能的母轮。

SELECT a1.*, p.lifeSpan, a2.* 
FROM
    ((Zoo AS z 
    INNER JOIN Plants AS p ON p.parent_id=z.id) 
    INNER JOIN Animal AS a1 ON a1.id=z.predator)
    INNER JOIN Animal AS a2 ON a2.id=z.prey

通知我丢弃了随函附上的那位母子。简便的表述并不需要。如果你对总统府有复合表述,那么你就象这样需要父母:

ON (p.parent_id=z.id AND p.foo = z.bar)

我建议抽样调查对我正确。 (如果它为你工作,则再次加入《惠予公约》条款。) 然而,我并不密切关注括号的安置,因为我利用“准入”设计师来组建联合体......并增加“支”发动机所需要的母体。

I urge you to do the same. If you re using an Access db from Dot.Net without having a copy of Access installed, you really should get a copy. Trying to use a database without that database s native development tools is an unreasonable challenge ... somewhat like trying to type while wearing mittens.

Answer 2

SELECT pred.col1 AS PredCol1, ..., pred.colx AS PredColx, 
       prey.col1 AS PreyCol1, ..., prey.colx AS PreyColx
    FROM Zoo z
        INNER JOIN Animal pred
            ON z.predator = pred.id
        INNER JOIN Animal prey
            ON z.prey = prey.id
    WHERE z.preyType = @carnivore

或者,你可能希望这样一些。

SELECT  Predator  AS AnimalType, pred.*
    FROM Zoo z
        INNER JOIN Animal pred
            ON z.predator = pred.id
    WHERE z.preyType = @carnivore
UNION ALL
SELECT  Prey  AS AnimalType, prey.*
    FROM Zoo z
        INNER JOIN Animal prey
            ON z.prey = prey.id
    WHERE z.preyType = @carnivore

Answer 3

表格中的条目

SELECT aPrey.Name as PreyName, aPredatior.Name as PredatorName 
FROM Zoo AS z 
LEFT JOIN Animal AS aPrey On aPrey.id= z.prey
LEFT JOIN Animal AS aPredatior On aPredatior.id= z.predator
WHERE z.preyType=@carnivore

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