SQL Server Denali : TRY_CONVERT(), a Good Addition

While working with different type of data, I have not found a single day, without data type conversion error. Sometime error could be just because of a single row, out of million of correct rows. SQL Server never mentions which row is the culprit, it just throw an error. Sometime you want to ignore those problematic rows but can’t because you have no other option to found those wrong data.You can correct them manually or write an intelligent query. Consider following simple example

CREATE TABLE #TempTable (Val1 VARCHAR(10))

INSERT INTO #TempTable

SELECT '2.01' UNION ALL

SELECT 'A2.4' UNION ALL

SELECT '6.51' UNION ALL

SELECT '$37' UNION ALL

SELECT '56'

GO

---Simple convert

SELECT CONVERT(float,Val1)  AS Val1

FROM #TempTable

Result of above select query is an error, because row:2 data can’t be converted into float.

Msg 8114, Level 16, State 5, Line 1

Error converting data type varchar to float.

So what will I do, so I can execute my query without any error.

SELECT CASE ISNUMERIC(Val1)

       WHEN 1 THEN 

              CASE LEFT(Val1,1)

              WHEN '$' THEN NULL

              ELSE CONVERT(float,Val1) END 

       ELSE NULL END AS Val1

To avoid such error, with out writing long quires, SQL Server Denali has introduced a new function TRY_CONVERT(). This function try to convert values according to your given format and if failed it will return NULL (instead of error). Let’s try this amazing function.

SELECT TRY_CONVERT(float,Val1)  AS Val1

FROM #TempTable

 

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