在SQL Server中将varchar数据类型转换为带存储过程错误的小数

Question

A Quantity column cannot be changed, it should be a decimal(18,5) , and an older SSIS package would actually use VB code to do this

 Dim q As Decimal
 q = Convert.ToDecimal(currentRow(16))

However, I am streamlining the process to import flat file into a new staging table

The value that is getting inserted into a database staging table is inserted as varchar(40) .

Example of one of the values:

0000000191185.18200-    

I want to convert that on the fly within a SQL Server query to a decimal(18,5) value in order to insert it into another final table.

Is it accurate to say that the conversion from varchar to decimal(18,5) should yield the value of -191185.18200 ?

I am trying to test casting of this and I get an error in T-SQL

select CAST(Quantity AS DECIMAL(18, 5)) 
from [DST].[DstPositionsStagingT]

Error is

Error converting data type varchar to numeric.

Quantity is the column in the table holding the value. What am I doing wrong?

Answer 1

An example of embedding simple cleaning in the body of the SQL in the hope that it's easier to read.

SELECT
  T.SecurityNumber,
  SUM(clean.quantity)                                AS total_quantity,
  SUM(CASE WHEN clean.quantity IS NULL THEN 1 END)   AS failed_conversions,
  MAX(T.Cusip)                                       AS CUSIP
FROM
  [DST].[DstPositionsStagingT]   AS T
CROSS APPLY
(
  SELECT CASE WHEN T.Quantity LIKE '%-'
              THEN - TRY_CONVERT(DECIMAL(18,5), LEFT(T.Quantity, LEN(T.Quantity) - 1))
              ELSE   TRY_CONVERT(DECIMAL(18,5),      T.Quantity                      )
         END
)
  AS clean(quantity)
GROUP BY
   T.SecurityNumber

Answer 2

0000000191185.18200- is not a valid format to convert to numeric. The valid format for negative value is - sign should be on the left. You can shift the sign the left or remove the - sign first convert to numeric and then add back

you can use case when check for such case and convert accordingly

declare @value  varchar(20)

select  @value  = '0000000191185.18200-'

select  case    when    right(@value, 1) = '-'
        then    -convert(decimal(18,2), replace(@value, '-', ''))
        else    convert(decimal(18,2), @value)
        end