XQuery [query()]: Heterogeneous sequences are not allowed: found 'xs:integer' and 'element(,xdt:untyped) *'

If we will execute following XQUERY sequence script in the sql server:

DECLARE @s AS XML = ''

SELECT @s.query('1,2,a,b')

We may get error message something like this:

Msg 2210, Level 16, State 1, Line 2

XQuery [query()]: Heterogeneous sequences are not allowed: found 'xs:integer +' and 'element(a,xdt:untyped) *'

Cause: Sql server doesn't support  a sequence with different types. In the above sequence 1 and 2 are of integer type while a and b are unknown type. All values in a sequence must be of same time.

Solution: Convert those values to higher data type. We can convert all the values in the sequence to string. For example:

DECLARE @s AS XML = ''

SELECT @s.query('"1","2","a","b"')

Output:

1 2 a b