Question

此查询用于证明一个概念，我最终将使用该概念定位具有特定值的所有列，然后创建名称/值对以导出到JSON。但是我被困住了。

我查询sql表中所有列的列表。然后，我想逐行浏览Table1中的列，并使用变量更新值以构造查询。例如，如果它通过列表读取Col4 =“Old text”，那么我想设置Col 4 =“New Text”的值

DECLARE @c varCHAR(100)
DECLARE ReadData CURSOR
FOR SELECT cname FROM sys.syscolumns WHERE creator = 'dbserver' AND tname = 'Table1' 
    DECLARE @RowCount INT

SET @RowCount = (SELECT COUNT(cname) FROM sys.syscolumns WHERE creator = 'dbserver' AND tname = 'Table1')
OPEN ReadData

DECLARE @I INT // iterator

SET @I = 1 // initialize
WHILE (@I <= @RowCount)
BEGIN
FETCH NEXT ReadData INTO @c

INSERT INTO serverdb.Table2 (cname)VALUES(@c)// this works inserting all 100 columns in the cname column of Table 2

UPDATE serverdb.Table1 SET @c = 'New text' WHERE @c = 'Old text'// this fails with a syntax error. @c is not being interpreted for the query. Note: If I hard code the @c var (for testing)to a known column name, the query works as well

SET @I = @I  + 1
END;

为什么update语句不能识别变量？我错过了什么？

Answer 1

当您使用如下所述的varibale时，它被视为字符串。

UPDATE serverdb.Table1 SET @c = 'New text' WHERE @c = 'Old text'

您需要创建动态查询。使用execute方法执行动态查询

declare @sql varchar(999)
SELECT @sql = 'UPDATE serverdb.Table1 SET '+ @c + '= ''New text'' WHERE '+ @c+ ' = ''Old text'' '
execute(@sql)

希望这有帮助

如何在Sybase更新语句中使用变量

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