Sql – Conversion failed when converting the varchar value ‘simple, ‘ to data type int

group-bysqlsql servertsql

I am struggling for a few days with this issue and I can't figure out how can I fix it.

I would like to group by my table on values 1,2,3,4,5 so I have created a temporary table with this values.

Now I have to INNER JOIN this table with other tables on a.value = #myTempTable.num.

BUT a.value is ntext so I need to CONVERT it what I actually did, but I am getting an error:

Conversion failed when converting the varchar value 'simple, ' to data
type int. (on line 7)

Create table #myTempTable
(
num int
)
insert into #myTempTable (num) values (1),(2),(3),(4),(5)

 SELECT a.name, CONVERT(INT, CONVERT(VARCHAR(12), a.value)) AS value, COUNT(*) AS pocet   
 FROM 
 (SELECT item.name, value.value 
  FROM mdl_feedback AS feedback 
  INNER JOIN mdl_feedback_item AS item 
       ON feedback.id = item.feedback
  INNER JOIN mdl_feedback_value AS value 
       ON item.id = value.item 
   WHERE item.typ = 'multichoicerated' AND item.feedback IN (43)
 ) AS a 
 INNER JOIN #myTempTable 
     on CONVERT(INT, CONVERT(VARCHAR(12), a.value)) = #myTempTable.num
 GROUP BY a.name, CONVERT(INT, CONVERT(VARCHAR(12), a.value)) ORDER BY a.name

 drop table #myTempTable

I am not getting this error without the last INNER JOIN 

INNER JOIN #myTempTable on CONVERT(INT, CONVERT(VARCHAR(12), a.value))
= #myTempTable.num

Could you help me please? I am desperate.

Thanks.

Best Answer

In order to avoid such error you could use CASE + ISNUMERIC to handle scenarios when you cannot convert to int.
Change 

CONVERT(INT, CONVERT(VARCHAR(12), a.value))

To 

CONVERT(INT,
        CASE
        WHEN IsNumeric(CONVERT(VARCHAR(12), a.value)) = 1 THEN CONVERT(VARCHAR(12),a.value)
        ELSE 0 END)

Basically this is saying if you cannot convert me to int assign value of 0 (in my example)

Alternatively you can look at this article about creating a custom function that will check if a.value is number: http://www.tek-tips.com/faqs.cfm?fid=6423

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