SQL insert into using CTE - tsql

Question

I am facing a performance issue due to "Insert into" statement in sql. I am using a CTE to select data from multiple tables and insert into other table. It was working just fine until yesterday. Select takes less than a minute to retrieve the data where as insert into taking forever. Can some one please help me in understanding what i am doing wrong. Any help is highly appreciated. Thanks.
Here is my code:
I am using this query in an SP. I am trying to load 220K records to 1.5M records table.
;with CTE_A
AS
(
SELECT A1, A2,...
FROM dbo.A with (nolock)
WHERE A1 = <some condition>
GROUP BY a.A1,a.A2 , a.A3
), CTE_C as
(
SELECT C1, C2,....
FROM dbo.B with (nolock)
WHERE a.C1 = <some condition>
GROUP BY a.c1,a.C2 , a.C3
)
INSERT INTO [dbo].MainTable
SELECT
A1, A2, A3 , C1, C2, C3
FROM
CTE_A ta with (nolock)
LEFT OUTER JOIN
CTE_C tc with (nolock) ON ta.a1 = tc.a1 and ta.b1 = tc.b1 and ta.c1 = tc.c1
LEFT OUTER JOIN
othertable bs with (nolock) ON usd_bs.c = s.c
AND (A1 BETWEEN bs.a1 AND bs.a1)
AND bs.c1 = 1

Answer 1

try this method (temp table instead cte), perfomance must be much higher for your task
IF OBJECT_ID('Tempdb..#CTE_A') IS NOT NULL
DROP TABLE #CTE_A
IF OBJECT_ID('Tempdb..#CTE_C') IS NOT NULL
DROP TABLE #CTE_C
-------------------------------------------------------------
SELECT A1 ,
A2 ,...
INTO #CTE_A --data set into temp table
FROM dbo.A WITH ( NOLOCK )
WHERE A1 = <some condition>
GROUP BY a.A1 ,
a.A2 ,
a.A3
-------------------------------------------------------------
SELECT C1 ,
C2 ,....
FROM dbo.B WITH ( NOLOCK )
INTO #CTE_C --data set into temp table
WHERE a.C1 = <some condition>
GROUP BY a.c1 ,
a.C2 ,
a.C3
INSERT INTO [dbo].MainTable
SELECT A1 ,
A2 ,
A3 ,
C1 ,
C2 ,
C3
FROM #CTE_A AS ta
LEFT JOIN #CTE_C AS tc ON ta.a1 = tc.a1
AND ta.b1 = tc.b1
AND ta.c1 = tc.c1
LEFT JOIN othertable AS bs ON usd_bs.c = s.c
AND ( A1 BETWEEN bs.a1 AND bs.a1 )
AND bs.c1 = 1