Select chunked data with row number using T-SQL - sql

Question

I have a SQL Server table containing a long text (varchar(max)) column and several key columns. I need to load this data into another table, but break the long text into chunks (varchar(4000)), so each row in the source table may become multiple rows in the target table.
Is there a way using T-SQL which can do this in one select statement and also provide a row_number? Sort of like partition over chunk size, if this makes sense.

Answer 1

Recursive CTE to split the string into 4000 character chunks (as a variation on this comma splitting thread: Turning a Comma Separated string into individual rows)
;WITH cte(SomeID, RowNum, DataItem, String) AS
(
SELECT
SomeID,
1,
LEFT(String, 4000),
case when len(String) > 4000 then
RIGHT(String, LEN(String) - 4000)
else
''
end
FROM myTable
UNION all
SELECT
SomeID,
RowNum + 1,
LEFT(String, 4000),
case when len(String) > 4000 then
RIGHT(String, LEN(String) - 4000)
else
''
end
FROM cte
WHERE
String > ''
)
SELECT *
FROM cte

Answer 2

You can use a recursive subquery:
with cte as (
select left(longtext, 4000) as val, 1 as rn,
stuff(longtext, 1, 4000, '') as rest
from t
union all
select left(rest, 4000), rn + 1,
stuff(longtext, 1, 4000, '') as rest
from cte
where longtext > ''
)
select *
from cte;
You probably want to include other columns as well, but your question doesn't mention them.
Also, if your text is really long (say more than a handful of chunks per row), then this is not going to be the most efficient method. There are related methods using recursive CTEs to solve this.