How Can I optimize this query (OR inside AND validation)? - sql

Question

I'm having problems with this query:
SELECT col1, col2,col3,...,coln FROM MyTable
WHERE col1 = #value1
AND
(
ISNULL(col2,'c') = ISNULL(#value2,ISNULL(col2,'c'))
OR
ISNULL(col3,'c') = ISNULL(#value2,ISNULL(col3,'c'))
)
AND coln = 'valueN'
I have to stop the execution, it's so slow. But editing:
SELECT col1, col2,col3,...,coln FROM MyTable
WHERE col1 = #value1
AND
(
ISNULL(col2,'c') = ISNULL(#value2,ISNULL(col2,'c'))
)
AND coln = 'valueN'
This query is faster. Can someone help me? How can I replace the or statement or replace the query but validating col1 and col2?.
Thanks.
UPDATE:
Thank you very much guys. Really my query does not use '=' but use 'Like', sorry about that. However I use your suggestions to build my query and it works fine:
SELECT col1, col2,col3,...,coln FROM MyTable
WHERE col1 like '%' + #value1 + '%'
AND
(
(#value2 IS NULL)
OR
(col2 IS NOT NULL AND col2 LIKE '%' + #value2 + '%')
OR
(col3 IS NOT NULL AND col3 LIKE '%' + #value2 + '%')
)
AND coln = 'valueN'
I use this query with a page where I have many fields to filter a search and I need that a col2 textbox apply to col3 in database too, I want to mean, only one textbox for name1 and name2 in database.
Sorry about my wrong question and thanks for your suggestions.

Answer 1

ISNULL(col2,'c') = ISNULL('value2',ISNULL(col2,'c'))
is the same as
col2 = 'value2' or (col2 is null and 'value2' is null)
Replace the occurrences and you will most likely have a better performance.
Update
There's one fundamental difference between this solution and the one proposed by #onedaywhen: when the value provided in 'value2' (which I suppose is just a parameter assembled into a SQL string) is NULL, OP only wants to bring back only records where col2 is NULL. Take a closer look into OP's logic, you will see that there. OP's logic always filters: when the parameter is NULL, OP wants records where col2 is NULL.
#onedaywhen's solution brings every record when the parameter is NULL. Although this is a very common query, it's not what OP is looking for.

Answer 2

ISNULL(col2,'c') = ISNULL(#value2,ISNULL(col2,'c'))
is the same as
( ( col2 = #value2 ) OR ( #value2 IS NULL ) )
I'm not sure if this will improve performance, though: I've read that, at least for SQL Server 2005 and earlier, to get an efficient, scalable and performant solution either use IF ELSE control of flow blocks (one per parameter combination) or use dynamic SQL.
UPDATE: ...and here's the proof:
Query 1: When the parameter is a value that is not null:
DECLARE #value2 VARCHAR(10);
SET #value2 = 'Apples';
WITH T
AS
(
SELECT *
FROM (
VALUES (1, 'When col2 is null', NULL),
(2, 'When col2 is the same value as #value2', 'Apples'),
(3, 'When col2 is not the same value as #value2', 'Oranges')
) AS T (ID, narrative, col2)
)
SELECT *,
CASE WHEN ISNULL(col2,'c') = ISNULL(#value2,ISNULL(col2,'c')) THEN 'T' END AS OP,
CASE WHEN ( ( col2 = #value2 ) OR ( #value2 IS NULL ) ) THEN 'T' END AS OneDayWhen,
CASE WHEN col2 = #value2 or (col2 is null and #value2 is null) THEN 'T' END AS Adrian
FROM T;
Output 1:
ID narrative col2 OP OneDayWhen Adrian
----------- ------------------------------------------ ------- ---- ---------- ------
1 When col2 is null NULL NULL NULL NULL
2 When col2 is the same value as #value2 Apples T T T
3 When col2 is not the same value as #value2 Oranges NULL NULL NULL
Note all agree for all rows :)
Query 2: When the parameter is a null:
DECLARE #value2 VARCHAR(10);
SET #value2 = NULL;
WITH T
AS
(
SELECT *
FROM (
VALUES (1, 'When col2 is null', NULL),
(2, 'When col2 is the same value as #value2', 'Apples'),
(3, 'When col2 is not the same value as #value2', 'Oranges')
) AS T (ID, narrative, col2)
)
SELECT *,
CASE WHEN ISNULL(col2,'c') = ISNULL(#value2,ISNULL(col2,'c')) THEN 'T' END AS OP,
CASE WHEN ( ( col2 = #value2 ) OR ( #value2 IS NULL ) ) THEN 'T' END AS OneDayWhen,
CASE WHEN col2 = #value2 or (col2 is null and #value2 is null) THEN 'T' END AS Adrian
FROM T;
Output 2:
ID narrative col2 OP OneDayWhen Adrian
----------- ------------------------------------------ ------- ---- ---------- ------
1 When col2 is null NULL T T T
2 When col2 is the same value as #value2 Apples T T NULL
3 When col2 is not the same value as #value2 Oranges T T NULL
Note OP and OneDayWhen match for all rows, Adrian only matches for row ID = 1.