How to get tsql TOP PERCENT with OFFSET

Question

select top 10 percent *
from sys.databases
order by database_id

I want to get the same 10 percent result using offset but this query works wrong

offset 0 rows
fetch next (select cast((count(*) * 10/100) as int ) from sys.databases) rows only

Answer 1

TOP PERCENT

Indicates that the query returns only the first expression percent of rows from the result set. Fractional values are rounded up to the next integer value.

Source

Meaning that TOP percent is rounding up, we could use the CEILING() function on a numeric value to get the same result.

You could change the query like this:

SELECT *
FROM sys.databases
ORDER BY database_id
OFFSET 0 ROWS
FETCH NEXT (SELECT CAST(CEILING((COUNT(*) * 10.0/100.0)) as int) FROM sys.databases) ROWS ONLY;

To get the same amount.

Issues with applying a filter.

If you add a where clause the results could differ, the reason being that in the changed query, you would need to add the where clause also on the query in the OFFSET FETCH part.

These two queries could return different results:

SELECT *
FROM sys.databases
where name not like '%A%'
ORDER BY database_id
OFFSET 0 ROWS
FETCH NEXT (SELECT CAST(CEILING((COUNT(*) * 10.0/100.0)) as int) FROM sys.databases) ROWS ONLY;


SELECT top 10 percent *
FROM sys.databases
where name not like '%A%'
ORDER BY database_id;

DB<>Fiddle

These two queries should return the same results:

SELECT *
FROM sys.databases
where name not like '%A%'
ORDER BY database_id
OFFSET 0 ROWS
FETCH NEXT (SELECT CAST(CEILING((COUNT(*) * 10.0/100.0)) as int) FROM sys.databases where name not like '%A%') ROWS ONLY;


SELECT top 10 percent *
FROM sys.databases
where name not like '%A%'
ORDER BY database_id;

DB<>Fiddle