如何在SQL Server中编写foreach？

Question

我正在尝试按照for-each的方式实现某些内容,我希望获取返回的select语句的ID并使用它们中的每一个.

DECLARE @i int
DECLARE @PractitionerId int
DECLARE @numrows int
DECLARE @Practitioner TABLE (
    idx smallint Primary Key IDENTITY(1,1)
    , PractitionerId int
)

INSERT @Practitioner
SELECT distinct PractitionerId FROM Practitioner

SET @i = 1
SET @numrows = (SELECT COUNT(*) FROM Practitioner)
IF @numrows > 0
    WHILE (@i <= (SELECT MAX(idx) FROM Practitioner))
    BEGIN

        SET @PractitionerId = (SELECT PractitionerId FROM @Practitioner WHERE idx = @i)

        --Do something with Id here
        PRINT @PractitionerId

        SET @i = @i + 1
    END

目前我有一些看起来像上面的东西,但我得到错误:

列名称'idx'无效.

有人可以

Answer 1

你似乎想用一个CURSOR.虽然大多数时候最好使用基于集合的解决方案,但有时候a CURSOR是最佳解决方案.如果不了解您的真实问题,我们无法帮助您:

DECLARE @PractitionerId int

DECLARE MY_CURSOR CURSOR 
  LOCAL STATIC READ_ONLY FORWARD_ONLY
FOR 
SELECT DISTINCT PractitionerId 
FROM Practitioner

OPEN MY_CURSOR
FETCH NEXT FROM MY_CURSOR INTO @PractitionerId
WHILE @@FETCH_STATUS = 0
BEGIN 
    --Do something with Id here
    PRINT @PractitionerId
    FETCH NEXT FROM MY_CURSOR INTO @PractitionerId
END
CLOSE MY_CURSOR
DEALLOCATE MY_CURSOR

Answer 2

假设PractitionerId列是唯一的,那么您可以使用以下循环

DECLARE @PractitionerId int = 0
WHILE(1 = 1)
BEGIN
  SELECT @PractitionerId = MIN(PractitionerId)
  FROM dbo.Practitioner WHERE PractitionerId > @PractitionerId
  IF @PractitionerId IS NULL BREAK
  SELECT @PractitionerId
END

Answer 3

您的选择计数和选择最大值应来自您的表变量而不是实际表

DECLARE @i int
DECLARE @PractitionerId int
DECLARE @numrows int
DECLARE @Practitioner TABLE (
    idx smallint Primary Key IDENTITY(1,1)
    , PractitionerId int
)

INSERT @Practitioner
SELECT distinct PractitionerId FROM Practitioner

SET @i = 1
SET @numrows = (SELECT COUNT(*) FROM @Practitioner)
IF @numrows > 0
    WHILE (@i <= (SELECT MAX(idx) FROM @Practitioner))
    BEGIN

        SET @PractitionerId = (SELECT PractitionerId FROM @Practitioner WHERE idx = @i)

        --Do something with Id here
        PRINT @PractitionerId

        SET @i = @i + 1
    END

Answer 4

通常（几乎总是），它的性能比游标更好，并且更简单：

    DECLARE @PractitionerList TABLE(PracticionerID INT)
    DECLARE @PractitionerID INT

    INSERT @PractitionerList(PracticionerID)
    SELECT PracticionerID
    FROM Practitioner

    WHILE(1 = 1)
    BEGIN

        SET @PracticionerID = NULL
        SELECT TOP(1) @PracticionerID = PracticionerID
        FROM @PractitionerList

        IF @PracticionerID IS NULL
            BREAK

        PRINT 'DO STUFF'

        DELETE TOP(1) FROM @PractitionerList

    END

Answer 5

我要说的是，所有内容都可能有效，但idx您选择的表中实际上并不存在该列。也许您打算选择@Practitioner：

WHILE (@i <= (SELECT MAX(idx) FROM @Practitioner))

因为那是在上面的代码中这样定义的：

DECLARE @Practitioner TABLE (
    idx smallint Primary Key IDENTITY(1,1)
    , PractitionerId int
)