[英]MySQL SELECT * fails on temporary table created by PREPARE using dynamic column and table names after first pass
[英]Pass Column names for a Select Query to retrieve from temporary table
我有一個臨時表,其中包含要從特定表(表A)中檢索的列名。
這是示例代碼:
Declare @temp table (ColumnNames varchar(30))
insert into @temp
values('Name'), ('Class'), ('School')
--select Query to retrieve only name,class and School columns
end
這里的表A包含10列以上
以下代碼完成了您所要求的:
Declare @temp table (ColumnNames varchar(30))
insert into @temp
values('Id'), ('Name')
DECLARE @ColumnNames nvarchar(max)
SELECT @ColumnNames = stuff((SELECT ',' + ColumnNames
FROM @temp
FOR XML PATH('')), 1,1, '')
EXEC (N'SELECT ' + @ColumnNames + N' FROM TheTable')
但是,這根本上是有問題的。 為什么在地球上,您需要將列名存儲在表變量中,以后再讀取它以構建sql語句?
DECLARE @SQLTOEXECUTE VARCHAR(MAX),
@Col VARCHAR(200)
DECLARE CURSOR curs FOR
SELECT ColumnNames FROM @temp
SET @SQLTOEXECUTE = 'SELECT '
OPEN curs
FETCH NEXT FROM Curs
INTO @Col
WHILE @@FETCH_STATUS = 0
BEGIN
SET @SQLTOEXECUTE = @SQLTOEXECUTE + @Col + ', '
FETCH NEXT FROM Curs
INTO @Col
END
CLOSE curs
DEALLOCATE curs
SET @SQLTOEXECUTE = ' FROM <Table name goes here>'
PRINT @SQLTOEXECUTE
這應該讓你走
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