通过SQL中的强制转换函数转换多行

Question

我有一个database table与name，address和monthly account expense作为每个月的列信息。

我想将month1的费用添加到month12表的accounts数据，但它是varchar数据类型，我想将其转换为float数据类型，并在查询中使用逻辑表达式获取所有费用的SUM（month 1） + month 2 + ... month12）应该大于10,000。

但我无法解决此问题，因为查询无法正常工作并且出现错误

请检查此查询，并告知我任何更改

SELECT name
      ,address
      ,CAST(([month1] + [month2]...[month12] AS float) AS 'total expense'
FROM Accounts_Table
WHERE name LIKE 'a%'
GROUP BY name, address, 'total expense'
HAVING 'total expense' > 10000

一些指针将很好地解决这个问题。

Answer 1

添加和转换month列的方式不正确。

此外，您将无法在[Total Expense]子句中在您声明它的同一查询中调用HAVING的别名。使用SUBQUERY。

见下文。

SELECT [name]
      ,[address]
      ,[Total Expense]
FROM (
    SELECT [name]
          ,[address]
          ,CAST([month1] AS float) +
           CAST([month2] AS float) +
           CAST([month3] AS float) +
           CAST([month4] AS float) +
           CAST([month5] AS float) +
           CAST([month6] AS float) +
           CAST([month7] AS float) +
           CAST([month8] AS float) +
           CAST([month9] AS float) +
           CAST([month10] AS float) +
           CAST([month11] AS float) +
           CAST([month12] AS float) AS [Total Expense]
    FROM [Accounts_Table]
    WHERE [name] LIKE 'a%') AS [src]
GROUP BY [name]
        ,[address]
        ,[Total Expense]
HAVING [Total Expense] > 10000

Answer 2

您必须在添加之前将每个varchar列转换为Float。看看解释

, (CAST( [month1] as float) + CAST([month2] as float)... CAST([month12] as Float))  AS 
   'total expense'