6

I am trying to make something like the following work:

WITH results(n, string ) AS (
            SELECT 1,'lol'
            UNION ALL
            SELECT n+1, string + ' lol'
            FROM results
            WHERE n<6
            )
            SELECT * FROM results

But SQL doesn't seem to recognize the string concatenation in the second column and returns the error:

Types don't match between the anchor and the recursive part in column "string" of recursive query "results".

My desired output would be something like

1, lol

2, lol lol

3, lol lol lol

and so on

1
  • You probably want a tally table/function here instead of an rCTE, it will be much faster – Charlieface Feb 28 at 17:02
7

You can cast it to varchar(2000) or varchar(max) depending on your needs so both should have the same data type and size
for value 1, it using an integer/int data type
From BOL related to CTE ,

  • The data type of a column in the recursive member must be the same as the data type of the corresponding column in the anchor member.
WITH results(n, string ) AS (
            SELECT 1,CAST('lol' as varchar(2000))
            UNION ALL
            SELECT n+1, CAST(string + ' lol' as varchar(2000))
            FROM results
            WHERE n<6
            )
            SELECT * FROM results

you can see the data type by using SQL_VARIANT_PROPERTY

WITH results(n, string, expressionType1, expressionType2) AS (
            SELECT 1,cast('lol' as varchar(2000)),
                    SQL_VARIANT_PROPERTY(1, 'BaseType'),
                    SQL_VARIANT_PROPERTY(cast('lol' as varchar(2000)), 'MaxLength')
            UNION ALL
            SELECT n+1, cast(string + ' lol' as varchar(2000)) ,
                SQL_VARIANT_PROPERTY(n+1, 'BaseType'),
                SQL_VARIANT_PROPERTY(cast(string + ' lol' as varchar(2000)), 'MaxLength')
            FROM results
            WHERE n<6
            )
            SELECT * FROM results

output:

n           string               expressionType1 expressionType2
1           lol                  int             2000
2           lol lol              int             2000
3           lol lol lol          int             2000
4           lol lol lol lol      int             2000
5           lol lol lol lol lol  int             2000
6           lol lol lol lol lol  int             2000

Data type for value/expression 1 can be checked by:

select SQL_VARIANT_PROPERTY(1,'basetype')
int
4
  • That works, thanks! How come you need to cast this one but it works without issue for n? i.e. you don't need to write out CAST(n as INT) – Oscar Feb 26 at 10:26
  • @Oscar, you can use CAST(n as INT) , but it is already of type int, so you don't need to specify. If you have bigint values , then it's another story... and should cast it to bigint – Sabin B Feb 26 at 11:09
  • Ah, I see now using the SQL_VARIANT_PROPERTY that unless casted as VARCHAR(MAX) 'lol' will be inferred the type VARCHAR(3) which is why it doesn't work otherwise. I find it strange that you're not allowed to simply declare the column type when initiating the CTE like: WITH results(n INT, string VARCHAR(MAX)). – Oscar Feb 26 at 15:00
  • Yes, SQL_VARIANT_PROPERTY it's of a great helper – Sabin B Feb 26 at 15:41

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