How to improve sql script performance - sql

Question

The following script is very slow when its run.
I have no idea how to improve the performance of the script.
Even with a view takes more than quite a lot minutes.
Any idea please share to me.
SELECT DISTINCT
( id )
FROM ( SELECT DISTINCT
ct.id AS id
FROM [Customer].[dbo].[Contact] ct
LEFT JOIN [Customer].[dbo].[Customer_ids] hnci ON ct.id = hnci.contact_id
WHERE hnci.customer_id IN (
SELECT DISTINCT
( [Customer_ID] )
FROM [Transactions].[dbo].[Transaction_Header]
WHERE actual_transaction_date > '20120218' )
UNION
SELECT DISTINCT
contact_id AS id
FROM [Customer].[dbo].[Restaurant_Attendance]
WHERE ( created > '2012-02-18 00:00:00.000'
OR modified > '2012-02-18 00:00:00.000'
)
AND ( [Fifth_Floor_London] = 1
OR [Fourth_Floor_Leeds] = 1
OR [Second_Floor_Bristol] = 1
)
UNION
SELECT DISTINCT
( ct.id )
FROM [Customer].[dbo].[Contact] ct
INNER JOIN [Customer].[dbo].[Wifinity_Devices] wfd ON ct.wifinity_uniqueID = wfd.[CustomerUniqueID]
AND startconnection > '2012-02-17'
UNION
SELECT DISTINCT
comdt.id AS id
FROM [Customer].[dbo].[Complete_dataset] comdt
LEFT JOIN [Customer].[dbo].[Aggregate_Spend_Counts] agsc ON comdt.id = agsc.contact_id
WHERE agsc.contact_id IS NULL
AND ( opt_out_Mail <> 1
OR opt_out_email <> 1
OR opt_out_SMS <> 1
OR opt_out_Mail IS NULL
OR opt_out_email IS NULL
OR opt_out_SMS IS NULL
)
AND ( address_1 IS NOT NULL
OR email IS NOT NULL
OR mobile IS NOT NULL
)
UNION
SELECT DISTINCT
( contact_id ) AS id
FROM [Customer].[dbo].[VIP_Card_Holders]
WHERE VIP_Card_number IS NOT NULL
) AS tbl

Answer 1

Wow, where to start...
--this distinct does nothing. Union is already distinct
--SELECT DISTINCT
-- ( id )
--FROM (
SELECT DISTINCT [Customer_ID] as ID
FROM [Transactions].[dbo].[Transaction_Header]
where actual_transaction_date > '20120218' )
UNION
SELECT
contact_id AS id
FROM [Customer].[dbo].[Restaurant_Attendance]
-- not sure that you are getting the date range you want. Should these be >=
-- if you want everything that occurred on the 18th or after you want >= '2012-02-18 00:00:00.000'
-- if you want everything that occurred on the 19th or after you want >= '2012-02-19 00:00:00.000'
-- the way you have it now, you will get everything on the 18th unless it happened exactly at midnight
WHERE ( created > '2012-02-18 00:00:00.000'
OR modified > '2012-02-18 00:00:00.000'
)
AND ( [Fifth_Floor_London] = 1
OR [Fourth_Floor_Leeds] = 1
OR [Second_Floor_Bristol] = 1
)
-- all of this does nothing because we already have every id in the contact table from the first query
-- UNION
-- SELECT
-- ( ct.id )
-- FROM [Customer].[dbo].[Contact] ct
-- INNER JOIN [Customer].[dbo].[Wifinity_Devices] wfd ON ct.wifinity_uniqueID = wfd.[CustomerUniqueID]
-- AND startconnection > '2012-02-17'
UNION
-- cleaned this up with isnull function and coalesce
SELECT
comdt.id AS id
FROM [Customer].[dbo].[Complete_dataset] comdt
LEFT JOIN [Customer].[dbo].[Aggregate_Spend_Counts] agsc ON comdt.id = agsc.contact_id
WHERE agsc.contact_id IS NULL
AND ( isnull(opt_out_Mail,0) <> 1
OR isnull(opt_out_email,0) <> 1
OR isnull(opt_out_SMS,0) <> 1
)
AND coalesce(address_1 , email, mobile) IS NOT NULL
UNION
SELECT
( contact_id ) AS id
FROM [Customer].[dbo].[VIP_Card_Holders]
WHERE VIP_Card_number IS NOT NULL
-- ) AS tbl

Answer 2

Where exists is generally faster than in as well.
Or conditions are generally slower as well, use more union statements instead.
And learn to use left joins correctly. If you have a where condition (other than where id is null) on the table on teh right side of a left join, it will convert to an inner join. If this is not what you want, then your code is currently giving you an incorrect result set.
See http://wiki.lessthandot.com/index.php/WHERE_conditions_on_a_LEFT_JOIN for an explanation of how to fix.

Answer 3

As stated in a comment optimize one at a time. See which one takes the longest and focus on that one.
union will remove duplicates so you don't need the distinct on the individual queries
On you first I would try this:
The left join is killed by the WHERE hnci.customer_id IN so you might as well have a join.
The sub-query is not efficient as cannot use an index on the IN.
The query optimizer does not know what in ( select .. ) will return so it cannot optimize use of indexes.
SELECT ct.id AS id
FROM [Customer].[dbo].[Contact] ct
JOIN [Customer].[dbo].[Customer_ids] hnci
ON ct.id = hnci.contact_id
JOIN [Transactions].[dbo].[Transaction_Header] th
on hnci.customer_id = th.[Customer_ID]
and th.actual_transaction_date > '20120218'
On that second join the query optimizer has the opportunity of which condition to apply first. Let say [Customer].[dbo].[Customer_ids].[customer_id] and [Transactions].[dbo].[Transaction_Header] each have indexes. The query optimizer has the option to apply that before [Transactions].[dbo].[Transaction_Header].[actual_transaction_date].
If [actual_transaction_date] is not indexed then for sure it would do the other ID join first.
With your in ( select ... ) the query optimizer has no option but to apply the actual_transaction_date > '20120218' first. OK some times query optimizer is smart enough to use an index inside the in outside the in but why make it hard for the query optimizer. I have found the query optimizer make better decisions if you make the decisions easier.
A join on a sub-query has the same problem. You take options away from the query optimizer. Give the query optimizer room to breathe.

Answer 4

try this, temptable should help you:
IF OBJECT_ID('Tempdb..#Temp1') IS NOT NULL
DROP TABLE #Temp1
--Low perfomance because of using "WHERE hnci.customer_id IN ( .... ) " - loop join must be
--and this "where" condition will apply to two tables after left join,
--so result will be same as with two inner joints but with bad perfomance
--SELECT DISTINCT
-- ct.id AS id
--INTO #temp1
--FROM [Customer].[dbo].[Contact] ct
-- LEFT JOIN [Customer].[dbo].[Customer_ids] hnci ON ct.id = hnci.contact_id
--WHERE hnci.customer_id IN (
-- SELECT DISTINCT
-- ( [Customer_ID] )
-- FROM [Transactions].[dbo].[Transaction_Header]
-- WHERE actual_transaction_date > '20120218' )
--------------------------------------------------------------------------------
--this will give the same result but with better perfomance then previouse one
--------------------------------------------------------------------------------
SELECT DISTINCT
ct.id AS id
INTO #temp1
FROM [Customer].[dbo].[Contact] ct
JOIN [Customer].[dbo].[Customer_ids] hnci ON ct.id = hnci.contact_id
JOIN ( SELECT DISTINCT
( [Customer_ID] )
FROM [Transactions].[dbo].[Transaction_Header]
WHERE actual_transaction_date > '20120218'
) T ON hnci.customer_id = T.[Customer_ID]
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
INSERT INTO #temp1
( id
)
SELECT DISTINCT
contact_id AS id
FROM [Customer].[dbo].[Restaurant_Attendance]
WHERE ( created > '2012-02-18 00:00:00.000'
OR modified > '2012-02-18 00:00:00.000'
)
AND ( [Fifth_Floor_London] = 1
OR [Fourth_Floor_Leeds] = 1
OR [Second_Floor_Bristol] = 1
)
INSERT INTO #temp1
( id
)
SELECT DISTINCT
( ct.id )
FROM [Customer].[dbo].[Contact] ct
INNER JOIN [Customer].[dbo].[Wifinity_Devices] wfd ON ct.wifinity_uniqueID = wfd.[CustomerUniqueID]
AND startconnection > '2012-02-17'
INSERT INTO #temp1
( id
)
SELECT DISTINCT
comdt.id AS id
FROM [Customer].[dbo].[Complete_dataset] comdt
LEFT JOIN [Customer].[dbo].[Aggregate_Spend_Counts] agsc ON comdt.id = agsc.contact_id
WHERE agsc.contact_id IS NULL
AND ( opt_out_Mail <> 1
OR opt_out_email <> 1
OR opt_out_SMS <> 1
OR opt_out_Mail IS NULL
OR opt_out_email IS NULL
OR opt_out_SMS IS NULL
)
AND ( address_1 IS NOT NULL
OR email IS NOT NULL
OR mobile IS NOT NULL
)
INSERT INTO #temp1
( id
)
SELECT DISTINCT
( contact_id ) AS id
FROM [Customer].[dbo].[VIP_Card_Holders]
WHERE VIP_Card_number IS NOT NULL
SELECT DISTINCT
id
FROM #temp1 AS T