Ошибка при преобразовании типа данных nvarchar к float sql

I also received the message «Error converting data type nvarchar to float». This was from a query in SQL Server Management Studio (SSMS) from SQL Server 2019.

In my case there were undecipherable characters in the source data, which was exported to CSV from Excel. Some columns were in the «Accounting» format, which has spaces, currency symbols, commas, and parenthesis, like this:

 - positive values: $ 123,456.78
 - negative values: $(123,456.78)

To account for this and resolve the error, I simply inserted a nested REPLACE() function to remove some characters and replace others, and wrapped it with IsNull() to return zero when necessary.

First I will describe:

• replace any $ , ) with nothing (aka null string or empty quotes '')
• replace any ( with - (aka hyphen or negative symbol)

And here is the SQL:

Original:
CONVERT(float, exp_TotalAmount)

Replacement:
CONVERT(float, IsNull(REPLACE(REPLACE(REPLACE(REPLACE(exp_TotalAmount,'(','-'),')',''),',',''),'$',''),0))

Here broken up for easier read, innermost first:
REPLACE(exp_TotalAmount, '(', '-')
REPLACE(X, ')', '')
REPLACE(X, ',', '')
REPLACE(X, '$', '')
IsNull (X, 0)
CONVERT(float, X)

This works for me?

DECLARE @tbl TABLE(test NVARCHAR(100));
INSERT INTO @tbl VALUES
 ('1248')
,('1248')
,('193.79')
,('201.56')
,('1475.71')
,('97.86')
,('97.86')
,('97.86')
,('125.49')
,('97.86')
,('447.83')
,('450')
,('492.99')
,('450');

SELECT *
     ,CAST(test AS FLOAT) AS CastedValue
FROM @tbl;

But the main question is: Why?

Hint 1: Float is the wrong type for this!

From the column name I take, that you are dealing with costs. The FLOAT type is absolutely to be avoided here! You should use DECIMAL or specialised types to cover money or currency values…

Hint 2: NVarchar is the wrong type for this!

And the next question is again: Why? Why are these values stored as NVARCHAR? If ever possible you should solve your problem here…

UPDATE

You edited your question and added this

insert into B () select[DestAddress], [COST]

I do not know the target table’s column names, but this should work

INSERT INTO B(ColumnForAddress,ColumnForCost)
SELECT CAST([COST] AS FLOAT),[DestAddress] FROM YourSourceTable

UPDATE 2

After all your comments I’m pretty sure, that there are invalid values within your numbers list. Use ISNUMERIC or — if you are using SQL-Server-2012+ even better TRY_CAST to find invalid values.

There are two things that need to be fixed. 

First, you need a test that can be used in SQL 2008R2 to determine if a number can be converted to a float.  A test that should work for you is to combine IsNumeric() with a regular expression that ensures that the string contains only characters that
are valid to be converted to a float.  So the following will test if the columns SQLVal and AccessVal can be converted to floats without error.

WHERE ISNUMERIC(SQLVal) = 1 AND SQLVal NOT LIKE '%[^0-9ED.+-]%' 
  AND ISNUMERIC(AccessVal) = 1 AND AccessVal NOT LIKE '%[^0-9ED.+-]%'

But your second problem is that SQL can process the query in any order it chooses.  So even if your WHERE clause only chooses rows that can be converted to float, SQL might convert ALL of the rows to float and only later check the WHERE clause 
and throw away the rows that don’t match the WHERE clause.  Of course, in your case, if SQL does this, you geet a conversion error before the WHERE clause is processed and the statement fails. 

There are two ways you can fix this, one of which leaves this as a single query, but will make your query longer and  more complex, the other will split your query into two queries.  That way might make your query less efficient depending on what
your are doing (although, in this case, I don’t think that will be a problem).

In the first way, you would change the WHERE clause of the query as above, and the everywhere where you do a convert you would add a CASE statement that makes sure you do not attempt to convert an invalid value.  So, for example, in your SELECT clause,
instead of

,ROUND(ABS(CONVERT(float, AccessVal,1)),0) as AccessFloat

you would use

,CASE WHEN ISNUMERIC(AccessVal) = 1 AND AccessVal NOT LIKE '%[^0-9ED.+-]%' 
   THEN ROUND(ABS(CONVERT(float, AccessVal,1)),0) END As AccessFloat

To be totally safe, you would need to make this change to add the CASE everywhere in your query where you have a CONVERT to float.

The second way would be to Create a temp table or table variable with one column named QA_AutoID.  Then insert into that table only rows which have valid floats in the columns.  Then use that temp table or variable in your query.  Since that
is now two SQL statements, the WHERE selecting only valid floats in the first query will always be done before any converts in the second query.  That would look something like

DECLARE @MyQA Table(QA_AutoID int /* or whatever the correct datatype is */);
INSERT @MyQA(QA_AutoID)
SELECT TOP 1 QA_AutoID 
	FROM QA 
	WHERE ISNUMERIC(SQLVal) = 1 AND SQLVal Not Like '%[^0-9ED.+-]%' 
          AND ISNUMERIC(AccessVal) = 1 AND AccessVal Not Like '%[^0-9ED.+-]%'


SELECT QA_AutoID, AccessVal, SQLVal
	,ROUND(ABS(CONVERT(float, AccessVal,1)),0) as AccessFloat
	,ROUND(ABS(CONVERT(float, SQLVal,1)),0) as SQLFloat
FROM QA
WHERE QA_AutoID in (
	SELECT TOP 1 QA_AutoID 
	FROM @MyQA
	)
AND ROUND(ABS(CONVERT(float, AccessVal,1)),0) <> ROUND(ABS(CONVERT(float, SQLVal,1)),0)
ORDER BY ROUND(ABS(CONVERT(float, AccessVal,1)),0) DESC
	,ROUND(ABS(CONVERT(float, SQLVal,1)),0) DESC

If I were you, I would probably choose the second method.

Tom

Sometimes, under certain circumstances, when you develop in SQL Server and especially when you try to convert a string data type value to a float data type value, you might get the error message: error converting data type varchar to float. As the error message describes, there is a conversion error and this is most probably due to the input parameter value you used in the conversion function.

Read more below on how you can easily resolve this problem.

Reproducing the Data Type Conversion Error

As mentioned above, the actual reason you get this error message, is that you are passing as a parameter to the CAST or CONVERT SQL Server functions, a value (varchar expression) that is invalid and cannot be converted to the desired data type.

Consider the following example:

-----------------------------------------
--Variable declaration and initialization
-----------------------------------------
DECLARE @value AS VARCHAR(50);

SET @value = '12.340.111,91';

--Perform the casting
SELECT CAST(@value AS FLOAT);

--or
--Perform the conversion
SELECT CONVERT(FLOAT, @value);
-----------------------------------------

If you execute the above code you will get an error message in the following type:

Msg 8114, Level 16, State 5, Line 6
Error converting data type varchar to float.

Another similar example where you get the same data type conversion error, is the below:

-----------------------------------------
--Variable declaration and initialization
-----------------------------------------
DECLARE @value2 AS VARCHAR(50);

SET @value2 = '12,340.15';

--Perform the casting
SELECT CAST(@value2 AS FLOAT);

--or
--Perform the conversion
SELECT CONVERT(FLOAT, @value2);

Why you get this Conversion Error

The exact reason for getting the error message in this case is that you are using the comma (,) as a decimal point and also the dots as group digit symbols. Though SQL Server considers as a decimal point the dot (.). Also when converting a varchar to float you must not use any digit grouping symbols.

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How to Resolve the Conversion Issue

In order for the above code to execute, you would need to first remove the dots (that is the digit grouping symbols in this case) and then replace the comma with a dot thus properly defining the decimal symbol for the varchar expression.

Note: You need to be careful at this point, in order to correctly specify the decimal symbol at the correct position of the number.

Therefore, you can modify the code of example 1 as per below example:

-------------------------------------------
--Variable declaration and initialization
-------------------------------------------
DECLARE @value AS VARCHAR(50);

SET @value = '12.340.111,91';

--Prepare the string for casting/conversion to float
SET @value = REPLACE(@value, '.', '');
SET @value = REPLACE(@value, ',', '.');

--Perform the casting
SELECT CAST(@value AS FLOAT);

--or
--Perform the conversion
SELECT CONVERT(FLOAT, @value);
-----------------------------------------

If you execute the above code you will be able to get the string successfully converted to float.

Similarly, you can modify the code of example 2 as per below example:

-----------------------------------------
--Variable declaration and initialization
-----------------------------------------
DECLARE @value2 AS VARCHAR(50);

SET @value2 = '12,340.15';

--Prepare the string for casting/conversion to float
SET @value2 = REPLACE(@value2, ',', '');

--Perform the casting
SELECT CAST(@value2 AS FLOAT);

--or
--Perform the conversion
SELECT CONVERT(FLOAT, @value2);

Again, if you execute the above code you will be able to get the string successfully converted to float.

*Note: Even though you can try changing the regional settings of the PC for setting the dot (.) as the decimal symbol, this will only affect the way the data is presented to you when returned from the casting/conversion call. Therefore, you still have to modify the varchar expression prior to the casting/conversion operation.

Regarding the message: error converting data type varchar to numeric

The above error message is similar to the one we examined in this article, therefore, the way for resolving the issue is similar to the one we described in the article. The only different for the numeric case, is that you will have to replace FLOAT with numeric[ (p[ ,s] )]. Learn more about the numeric data type in SQL Server and how to resolve the above conversion issue, by reading the relevant article on SQLNetHub.

Watch the Live Demonstration on the VARCHAR to FLOAT Data Type Conversion Error

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How to resolve the error: Error converting data type varchar to float

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