Question

我有一个查询，预期达到以下目的

 If((Select count(*) from table1 where product = 'carrot')< 5)
Begin
Select Top (5 - (Select count(*) from table1 where product = 'carrot'))
id, product From table2
WHere id NOT IN
(Select id from table1) AND product = 'carrot'
Order by newid()
END

我想做的是Union或Union都说另一个产品土豆

If((Select count(*) from table1 where product = 'potato')< 5)
Begin
Select Top (5 - (Select count(*) from table1 where product = 'potato'))
id, product From table2
WHere id NOT IN
(Select id from table1) AND product = 'potato'
Order by newid()
END

当我在IF之间或END之后添加UNION时，我一直收到语法错误。这是可能的还是另一种更好的方法。...

我正在做的是尝试选择一个随机的胡萝卜样本，首先我想检查一下表1中是否有5个胡萝卜。如果我不运行示例。如果我没有5根胡萝卜，请运行采样器并返回5根胡萝卜。然后，我通过ID筛选出它们是否已存在于表1中。然后从新样本中减去总数为5的计数。

效果很好，现在我想运行其他产品，例如生菜，土豆等... 但是我想要一个UNION或UNION All。希望是有道理的。

Answer 1

我很想知道这种方式是否有效-

Select Top (5 - (Select count(*) from table1 where product = 'carrots')< 5)
id
, product 
From table2
WHere id NOT IN (Select id from table2)
    AND (Select count(*) from table1 where product = 'carrots')< 5)
UNION ALL
Select Top (5 - (Select count(*) from table1 where product = 'potatoes')< 5)
id
, product 
From table2
WHere id NOT IN (Select id from table2) 
    AND (Select count(*) from table1 where product = 'potatoes')< 5)

您的风格很有趣，感觉是过程性的，而不是基于集合的。

Answer 2

您可以尝试这种方式

If(((Select count(*) from table1 where product = 'carrot'< 5) and (Select count(*) from table1 where product ='potato' <5))
) 
Begin

Select Top (5 - (Select count(*) from table1 where product = 'carrot')) id, product 
From table2 
WHere id NOT IN (Select id from table1) AND product = 'carrot' Order by newid()

Union all


Select Top (5 - (Select count(*) from table1 where product = 'potato')) id, product From table2 
WHere id NOT IN (Select id from table1) AND product = 'potato' Order by newid()

END

Answer 3

如您所知，SQL中的

IF语句在SQL中不充当子查询或行集。它们仅用于分支控制流。

您可以采用以下基于集合的方法：

SELECT ProdSamples.*
FROM
    (
    SELECT Table2.*, ROW_NUMBER() OVER (PARTITION BY table2.Product ORDER BY NEWID()) RowNum
    FROM Table2
    LEFT JOIN Table1
    ON Table1.id = Table2.id
    WHERE Table1.id IS NULL
    ) ProdSamples
JOIN
    (
    SELECT Product, COUNT(*) ProdCount
    FROM Table1
    GROUP BY Product
    ) ProdCounts
ON ProdSamples.Product = ProdCounts.Product
    AND ProdSamples.RowNum <= (5 - ProdCounts.ProdCount)

第一个子查询ProdSamples返回Table2中id中没有Table1的所有产品。 RowNum字段按Product划分的随机顺序对它们进行排名。

第二个子查询ProdCounts是Table1中每个产品的记录数。然后它将这些子查询连接在一起，仅返回ProdSamples处RowNum小于或等于要返回的样本数的记录。

MSSQL Union使用if语句的所有两个查询

3 个答案: