Question

使用： SQL Server 2008 Management Studio，T-SQL

问题描述：我基本上有两个带有AccountNumber列的表格。在一个表中，它存储为NUMERIC，在另一个表中，它存储为VARCHAR（遗憾的是，此数据类型差异无法更改）。

为了保持一致性，为了使它们都进入数值数据类型，我尝试的解决方案仅在LEFT JOIN表中VARCHAR转换为AccountNumber列到NUMERIC。

工作正常，查询将会运行。

但是，一旦我向它添加WHERE子句，它就会崩溃并显示如下所示的错误。正如您所看到的，使用WHERE子句，我实际上只是在查询特定的NUMERIC} AccountNumber。

当AccountNumber出来的LEFT JOIN列为NUMERIC时，为什么会出现此转化错误？

/*
Assumptions:
    A.AFIELD is numeric
    B.BFIELD is varchar

Result:
    Msg 8114, Level 16, State 5, Line 10
    Error converting data type varchar to numeric.
*/

SELECT A.AccountNumber, B.AccountNumber
FROM A
LEFT JOIN 
    (SELECT CONVERT(NUMERIC, B.AccountNumber) AccountNumber
     FROM B
     WHERE ISNUMERIC(B.AccountNumber) = 1) B ON B.AccountNumber = A.AccountNumber
WHERE A.AccountNumber = 1234567890
/*NOTE: I am searching the originally numeric AccountNumber field for a numeric, yet it's erroring out*/

Answer 1

您应该执行转换为VARCHAR：

select A.AccountNumber, B.AccountNumber
from A
left join
    (
    select AccountNumber
    from B
    where ISNUMERIC(B.AccountNumber)=1
    ) B on B.AccountNumber = CONVERT(VARCHAR(10),A.AccountNumber)
where A.AccountNumber = 1234567890;

Answer 2

也许我的评论，“它告诉你，B中有一个值（无法转换为数字）”还不够明确。试试这个：

select A.AccountNumber, B.AccountNumber
from A
left join
    (
    select CONVERT(numeric,B.AccountNumber) AccountNumber
    from B
    where ISNUMERIC(B.AccountNumber)=1
    ) B on coalesce(B.AccountNumber,0) = A.AccountNumber
where A.AccountNumber = 1234567890;

这是一个简单的演示：

DECLARE @t1 TABLE
  (
    accountnumber NUMERIC
  );
DECLARE @t2 TABLE
  (
    accountnumber VARCHAR(20)
  );

INSERT  @t1 ( [accountnumber] )
VALUES  ( 1 ),
        ( 2 ),
        ( 3 );

INSERT  @t2 ( [accountnumber] )
VALUES  ( '1' ),
        ( '3' ),
        ( 'NonConvertible' );


SELECT  A.accountnumber, B.accountNumber
FROM    @t1 AS [A]
LEFT JOIN (
            SELECT
                CASE 
                    -- Still not 100% safe because ISNUMERIC isn't
                    WHEN ISNUMERIC(B.accountnumber) = 1
                    THEN CONVERT(NUMERIC, accountnumber) 
                    ELSE CONVERT(NUMERIC, NULL)
                END AS accountNumber
            FROM    @t2 AS [B]
            WHERE   ISNUMERIC(accountNumber) = 1
--          ) B ON B.accountNumber = A.accountnumber
          ) B ON COALESCE(B.accountNumber, 0) = A.accountnumber
WHERE   A.accountnumber = 1;

添加WHERE后，SQL CONVERT无效

2 个答案: