sql-server - 如何在 SQL Server 中编写 foreach？

Question

我正在尝试按照 for-each 的方式实现一些目标，我想在其中获取返回的 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，但我得到了错误：

列名“idx”无效。

score 397 · Accepted Answer

您似乎想使用CURSOR. 虽然大多数时候最好使用基于集合的解决方案，但有时 aCURSOR是最好的解决方案。在不了解您的实际问题的情况下，我们无法为您提供更多帮助：

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

score 159 · Accepted Answer

假设 PractitionerId 列是唯一的，那么可以使用下面的循环

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

score 42 · Accepted Answer

这通常（几乎总是）比游标执行得更好并且更简单：

DECLARE @PractitionerList TABLE(PracticionerID INT)
DECLARE @PracticionerID 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

score 21 · Accepted Answer

您的选择计数和选择最大值应该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

score 6 · Accepted Answer

我会说一切都可能有效，只是该列idx实际上并不存在于您从中选择的表中。也许您打算选择@Practitioner：

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

因为这是在上面的代码中定义的：

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

score 4 · Accepted Answer

以下行在您的版本中是错误的：

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

（缺少@）

更改命名约定可能是一个想法，以便表格更加不同。

score 3 · Accepted Answer

虽然游标通常被认为是可怕的邪恶，但我相信这是 FAST_FORWARD 游标的一个例子——在 TSQL 中你可以得到最接近 FOREACH 的东西。

score 3 · Accepted Answer

这是更好的解决方案之一。

DECLARE @i int
            DECLARE @curren_val int
            DECLARE @numrows int
            create table #Practitioner (idx int IDENTITY(1,1), PractitionerId int)
            INSERT INTO #Practitioner (PractitionerId) values (10),(20),(30)
            SET @i = 1
            SET @numrows = (SELECT COUNT(*) FROM #Practitioner)
            IF @numrows > 0
            WHILE (@i <= (SELECT MAX(idx) FROM #Practitioner))
            BEGIN

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

                --Do something with Id here
                PRINT @curren_val
                SET @i = @i + 1
            END

在这里，我在表中添加了一些值，因为最初它是空的。

我们可以访问或者我们可以在循环体中做任何事情，我们可以通过在表定义中定义它来访问 idx。

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

                --Do something with Id here

                PRINT @curren_val
                SET @i = @i + 1
            END

score 3 · Accepted Answer

我制作了一个对任何表执行FOREACHwith的过程。CURSOR

使用示例：

CREATE TABLE #A (I INT, J INT)
INSERT INTO #A VALUES (1, 2), (2, 3)
EXEC PRC_FOREACH
    #A --Table we want to do the FOREACH
    , 'SELECT @I, @J' --The execute command, each column becomes a variable in the same type, so DON'T USE SPACES IN NAMES
   --The third variable is the database, it's optional because a table in TEMPB or the DB of the proc will be discovered in code

结果是每行有 2 个选择。UPDATE和 break the的语法FOREACH写在提示中。

这是过程代码：

CREATE PROC [dbo].[PRC_FOREACH] (@TBL VARCHAR(100) = NULL, @EXECUTE NVARCHAR(MAX)=NULL, @DB VARCHAR(100) = NULL) AS BEGIN

    --LOOP BETWEEN EACH TABLE LINE            

IF @TBL + @EXECUTE IS NULL BEGIN
    PRINT '@TBL: A TABLE TO MAKE OUT EACH LINE'
    PRINT '@EXECUTE: COMMAND TO BE PERFORMED ON EACH FOREACH TRANSACTION'
    PRINT '@DB: BANK WHERE THIS TABLE IS (IF NOT INFORMED IT WILL BE DB_NAME () OR TEMPDB)' + CHAR(13)
    PRINT 'ROW COLUMNS WILL VARIABLE WITH THE SAME NAME (COL_A = @COL_A)'
    PRINT 'THEREFORE THE COLUMNS CANT CONTAIN SPACES!' + CHAR(13)
    PRINT 'SYNTAX UPDATE:

UPDATE TABLE
SET COL = NEW_VALUE
WHERE CURRENT OF MY_CURSOR

CLOSE CURSOR (BEFORE ALL LINES):

IF 1 = 1 GOTO FIM_CURSOR'
    RETURN
END
SET @DB = ISNULL(@DB, CASE WHEN LEFT(@TBL, 1) = '#' THEN 'TEMPDB' ELSE DB_NAME() END)

    --Identifies the columns for the variables (DECLARE and INTO (Next cursor line))

DECLARE @Q NVARCHAR(MAX)
SET @Q = '
WITH X AS (
    SELECT
        A = '', @'' + NAME
        , B = '' '' + type_name(system_type_id)
        , C = CASE
            WHEN type_name(system_type_id) IN (''VARCHAR'', ''CHAR'', ''NCHAR'', ''NVARCHAR'') THEN ''('' + REPLACE(CONVERT(VARCHAR(10), max_length), ''-1'', ''MAX'') + '')''
            WHEN type_name(system_type_id) IN (''DECIMAL'', ''NUMERIC'') THEN ''('' + CONVERT(VARCHAR(10), precision) + '', '' + CONVERT(VARCHAR(10), scale) + '')''
            ELSE ''''
        END
    FROM [' + @DB + '].SYS.COLUMNS C WITH(NOLOCK)
    WHERE OBJECT_ID = OBJECT_ID(''[' + @DB + '].DBO.[' + @TBL + ']'')
    )
SELECT
    @DECLARE = STUFF((SELECT A + B + C FROM X FOR XML PATH('''')), 1, 1, '''')
    , @INTO = ''--Read the next line
FETCH NEXT FROM MY_CURSOR INTO '' + STUFF((SELECT A + '''' FROM X FOR XML PATH('''')), 1, 1, '''')'

DECLARE @DECLARE NVARCHAR(MAX), @INTO NVARCHAR(MAX)
EXEC SP_EXECUTESQL @Q, N'@DECLARE NVARCHAR(MAX) OUTPUT, @INTO NVARCHAR(MAX) OUTPUT', @DECLARE OUTPUT, @INTO OUTPUT

    --PREPARE TO QUERY

SELECT
    @Q = '
DECLARE ' + @DECLARE + '
-- Cursor to scroll through object names
DECLARE MY_CURSOR CURSOR FOR
    SELECT *
    FROM [' + @DB + '].DBO.[' + @TBL + ']

-- Opening Cursor for Reading
OPEN MY_CURSOR
' + @INTO + '

-- Traversing Cursor Lines (While There)
WHILE @@FETCH_STATUS = 0
BEGIN
    ' + @EXECUTE + '
    -- Reading the next line
    ' + @INTO + '
END
FIM_CURSOR:
-- Closing Cursor for Reading
CLOSE MY_CURSOR

DEALLOCATE MY_CURSOR'

EXEC SP_EXECUTESQL @Q --MAGIA
END

score 2 · Accepted Answer

我想出了一个非常有效的，（我认为）可读的方法来做到这一点。

    1. create a temp table and put the records you want to iterate in there
    2. use WHILE @@ROWCOUNT <> 0 to do the iterating
    3. to get one row at a time do, SELECT TOP 1 <fieldnames>
        b. save the unique ID for that row in a variable
    4. Do Stuff, then delete the row from the temp table based on the ID saved at step 3b.

这是代码。抱歉，它使用我的变量名而不是问题中的变量名。

            declare @tempPFRunStops TABLE (ProformaRunStopsID int,ProformaRunMasterID int, CompanyLocationID int, StopSequence int );    

        INSERT @tempPFRunStops (ProformaRunStopsID,ProformaRunMasterID, CompanyLocationID, StopSequence) 
        SELECT ProformaRunStopsID, ProformaRunMasterID, CompanyLocationID, StopSequence from ProformaRunStops 
        WHERE ProformaRunMasterID IN ( SELECT ProformaRunMasterID FROM ProformaRunMaster WHERE ProformaId = 15 )

    -- SELECT * FROM @tempPFRunStops

    WHILE @@ROWCOUNT <> 0  -- << I dont know how this works
        BEGIN
            SELECT TOP 1 * FROM @tempPFRunStops
            -- I could have put the unique ID into a variable here
            SELECT 'Ha'  -- Do Stuff
            DELETE @tempPFRunStops WHERE ProformaRunStopsID = (SELECT TOP 1 ProformaRunStopsID FROM @tempPFRunStops)
        END

sql-server - 如何在 SQL Server 中编写 foreach？

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