SQL Server - 将字符串转换为浮点数，并显示N / A.

Question

I have a flat file that I loaded into SQL Server using the import wizard. All columns are stored as nchar(50).

I'm now trying to convert the table to a new table with various types (char, float, int, etc).

There is one column that I'd like to convert to float but it contains N/A strings.

I checked that there weren't any other weird string using this:

SELECT col1, count(*)
from tab1
where ISNUMERIC(col1) <> 1
group by col1

Then I wrote a CASE statement to do the conversion:

SELECT CASE WHEN col1 = 'N/A' THEN NULL ELSE CAST(col1 AS FLOAT) END col1
INTO tab2
FROM tab1

But I'm getting this error message:

Msg 8114, Level 16, State 5, Line 1
Error converting data type nvarchar to float.

Any idea what's causing this?

Answer 1

If 2012+ Use try_convert()

SELECT col1, count(*)
from tab1
where try_convert(float,col1) is null
group by col1

Answer 2

如果要忽略浮动的无效字符，可以使用try_convert，如下所示

Select try_convert(float, col1) as col1 from yourtable

Answer 3

Careful on using ISNUMERIC() for this. It can return some false positives. For example...

select isnumeric('$')
select isnumeric('1e4') 

This should show you what is causing the error.

select * from table where column like '%[^0-9\.]%' escape '\'

You can use this in a where clause, or use TRY_CONVERT()

Answer 4

You aren't doing the type conversion from the String to the float. In your SQL statements you need to explicitly cast the original column type from nvarchar to float. Something like this might work:

SELECT
    CASE
        WHEN col1 = 'N/A' THEN NULL
        ELSE CAST(col1 AS FLOAT) 
    END col1
INTO tab2
FROM tab1