How to delete row from a heap with a batch size 10000 - sql-delete

Question

No supported-
DELETE TOP(10000) FROM dataArchival.MyTable
WHERE DateLocal BETWEEN '2018-03-01' AND '2018-10-01'
delete dataArchival.MyTable
from dataArchival.MyTable d,#myTemp d2
where d.DateLocal=d2.DateLocal
delete d from dataArchival.MyTable d
(
SELECT
*,
RN = ROW_NUMBER() OVER(ORDER BY (SELECT NULL))
FROM dataArchival.MyTable
where DateLocal BETWEEN '2018-03-01' AND '2018-10-01'
)A where A.RN <=10000
And ofcource CTE and ##rowcount are also not supported.

Answer 1

As per the documentation Azure SQL Data Warehouse does not support TOP(n) with DELETE at this point:
-- Syntax for Azure SQL Data Warehouse and Parallel Data Warehouse
DELETE FROM [database_name . [ schema ] . | schema. ] table_name
[ WHERE <search_condition> ]
[ OPTION ( <query_options> [ ,...n ] ) ]
[; ]
However you can script for a similar effect, eg this example is adapted from this example to delete by date:
CREATE TABLE #tmp
WITH (
DISTRIBUTION = ROUND_ROBIN
)
AS
SELECT
ROW_NUMBER() OVER( ORDER BY ( SELECT NULL ) ) AS rowId,
DateLocal
FROM ( SELECT DISTINCT DateLocal FROM dataArchival.MyTable ) x;
DECLARE #sql_code NVARCHAR(4000) = 'DELETE dataArchival.MyTable WHERE DateLocal = #p1'
DECLARE #nbr_statements INT = ( SELECT COUNT(*) FROM #tmp ),
#i INT = 1;
WHILE #i <= #nbr_statements
BEGIN
DECLARE #p1 DATE = ( SELECT DateLocal FROM #tmp WHERE rowId = #i );
EXEC sp_executesql #sql_code, N'#p1 DATE', #p1
SET #i +=1;
END
You could easily alter this example to delete in batches of 10,000 if deleting by date is unsatisfactory. There is an additional example of batching up deletes here:
https://learn.microsoft.com/en-us/azure/sql-data-warehouse/sql-data-warehouse-develop-best-practices-transactions#minimize-logging-with-small-batches