SQL SERVER INSERT STATEMENT WITH LOOP Needs Optimized - sql-server

Question

I have SQL Statement running in SQL server 2014.
I have 3 columns: id, text1, text2
Inserting records in text1, text2
text1 is nvarchar
text2 is varchar
so far inserted 1.2 million rows in about 3.5 hrs
trying to insert 3 million need help in reduce time for insert
CODE:
DECLARE #i as int
SET #i = 0
WHILE #i < 3000000
BEGIN
SET #i = #i + 1
insert into test (text1 , text2)
values(N'你好','VJ'+ cast(#i as varchar(20)))
END

Answer 1

Here is another way to do it ... It finish pretty fast ... less then 5 sec on my SQL server
if object_id('tempdb..#Numbers') is not null drop table #Numbers
create table #Numbers (Num int)
insert into #Numbers (Num)
SELECT TOP (3000000) n = CONVERT(INT, ROW_NUMBER() OVER (ORDER BY s1.[object_id]))
FROM sys.all_objects AS s1 CROSS JOIN sys.all_objects AS s2
OPTION (MAXDOP 1);
if object_id('tempdb..#test') is not null drop table #test
create table #test (text1 nvarchar(50), text2 nvarchar(50))
insert into #test (text1, text2)
select N'你好' [text1], 'VJ' + cast(Num as nvarchar) [text2] from #Numbers

Answer 2

You can try like this
WITH CTE_TEST
AS
(
SELECT N'你好' AS CODE,'VJ'+ cast(1 as varchar(20)) NAME, 1 AS VCOUNT
UNION ALL
SELECT N'你好' ,'VJ'+ cast(VCOUNT+1 as varchar(20)) NAME, VCOUNT+1 AS VCOUNT
FROM CTE_TEST
WHERE VCOUNT+1 < 3000000
)
INSERT INTO test (text1 , text2)
SELECT CODE,NAME FROM CTE_TEST
OPTION (MAXRECURSION 0)
You can use your additional logic inside the CTE, and simply insert the result set to actual table. Here the insert statement is outside the loop (1 insert statement with 3000000 records) , so it will faster than inserting the record inside a loop 3000000 times (3000000 insert statements with 1 record each)
By default the MAXRECURSION is 100 to avoid infinite looping, here you need to override this (but it is not a good practice).

Answer 3

An alternative that does not use recursive CTE is to use a known table with many enough records, so that you can iterate against it:
-- generation parameters
declare #batchCount INT = 100000
declare #totalCount INT = 30000000
declare #loopCount INT = #totalCount / #batchCount
DECLARE #i as int = 0
-- loops are slow, but here we have only a few
WHILE (#i < #loopCount)
BEGIN
-- insert can be put just here to actually perform the insert
-- ROW_NUMBER gives us the numbering, but order does not matter, so using SELECT 1
select TOP (#batchCount) N'你好','VJ'+ cast(#i * #batchCount + ROW_NUMBER() OVER (ORDER BY (SELECT 1)) as varchar(20))
from sys.messages
SET #i = #i + 1
END
sys.messages is a pretty large table (at least 200K records), so it can safely be used for batches of 100K.
Time using recursive CTE: 51s
Time using above solution: 28s
(tested on a SQL Server 2014 Express instance, SELECT only)