Question

凭借我有限的SQL知识，我无法弄清楚这一点。以下是什么问题：

DECLARE @Id int
DECLARE @Name varchar(40)

WHILE EXISTS
        (
        SELECT TOP 1 @Name = Name, @Id=ID FROM MyTable c WHERE <CONDITION>
        )
BEGIN
    SOME MORE SQL using @Id and @Name
END

我在@Name = Name

附近收到语法错误

修改

要为问题添加更多上下文，我有两个名为Category (ID, Name, ParentID)和Account(ID, Name, CategoryID)的表。

Categories有3个等级。

根
分类
子类别

这是使用递归关系（ParentID＆gt; CategoryID）实现的。要解决的问题是，如果有任何属于X类（{2级）的Accounts，我们必须

创建一个与X
让Y成为那个X的孩子
将所有帐户从X移至Y

这是我写的原始剧本：

DECLARE @Id int
DECLARE @Name varchar(40)

WHILE EXISTS(
        SELECT TOP 1 @Name=Name, @Id=CategoryID FROM Category c WHERE 
        ParentID = (SELECT TOP 1 CategoryID FROM Category WHERE Name = 'Root') AND
        (SELECT COUNT(*) FROM Account WHERE CategoryID = c.CategoryID) > 0
        )
BEGIN
    INSERT INTO Category(Name, ParentID) VALUES(@Name, @Id)
    UPDATE Account SET CategoryID = @@IDENTITY WHERE CategoryID = @Id  
END

Answer 1

您可以使用CURSOR循环：

CREATE TABLE MyTable(ID INT, Name VARCHAR(100));
INSERT INTO Mytable(ID, Name) VALUES (1,10),(2,20);

DECLARE @Id int;
DECLARE @Name varchar(40);

DECLARE cur CURSOR FAST_FORWARD FOR SELECT Name,ID FROM MyTable c WHERE 1=1;

OPEN cur;
FETCH NEXT FROM cur INTO @Id, @Name;

WHILE @@FETCH_STATUS = 0
BEGIN
   SELECT @Id,@Name;   

   FETCH NEXT FROM cur INTO @Id, @Name;
END;

CLOSE cur;
DEALLOCATE cur;

的 LiveDemo

请注意，没有明确TOP 1的{{1}}可能会在执行之间产生不同的结果。

EXISTS：

EXISTS子查询

请注意，ORDER BY不是子查询，而是赋值。

SELECT @ID = id, @Name = Name

的 LiveDemo 2

Answer 2

没有必要使用While，你可以使用if条件代替while这样 - “

DECLARE @Id int
DECLARE @Name varchar(40)

SELECT TOP 1 @Name = Name, @Id=ID FROM MyTable c WHERE <CONDITION>

-- Now Check for @Name and @ID
IF ISNULL(@Name, '') <> '' AND ISNULL(@Id, 0) <> 0
BEGIN
      SOME MORE SQL using @Id and @Name
END

<强> EDITED

IF EXISTS(SELECT 1 FROM Category c 
            WHERE ParentID = (SELECT TOP 1 CategoryID FROM Category WHERE Name = 'Root')  
            AND (SELECT COUNT(*) FROM Account WHERE CategoryID = c.CategoryID) > 0
        )
BEGIN

     SELECT TOP 1 @Name=Name, @Id=CategoryID FROM Category c 
        WHERE ParentID = (SELECT TOP 1 CategoryID FROM Category WHERE Name = 'Root') 
        AND (SELECT COUNT(*) FROM Account WHERE CategoryID = c.CategoryID) > 0

    INSERT INTO Category(Name, ParentID) 
      VALUES(@Name, @Id)

    SET @CategoryID = SCOPE_IDENTITY()

    UPDATE Account SET CategoryID = @CategoryID WHERE CategoryID = @Id  

END

Answer 3

SELECT @local_variable (Transact-SQL)

不能使用包含变量赋值的SELECT语句也执行典型的结果集检索操作。

在这里你使用EXISTS来检索数据，所以我猜你不能在子查询中使用赋值。

尝试使用BREAK实现等效的WHILE TRUE循环。

{{1}}

Answer 4

将此用于检查记录存在

WHILE EXISTS
    (
    SELECT TOP 1 * FROM MyTable c WHERE <CONDITION>
    )
BEGIN
    SELECT TOP 1 @Name = Name, @Id=ID FROM MyTable c WHERE <CONDITION>

-- and do here what you want
END

SELECT语句中的语法错误

修改

4 个答案: