String manipulation in Recursive CTE
-
16-03-2021 - |
Question
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
Solution
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
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