I'm a sales-force developer, I got a requirement to write a SQL query and I did it, but the performance in very low. Could you please help me here?
My query is like this:
select col1, col2,col3,col4
from table1
where col1 is not null
and col2='ABC'
and (col3 IN (SELECT field1 FROM table 2)
OR col4 in('A','B','C'))
Is there someway I can optimize this for better performance?
Update
I used left outer join to achieve it, Is that the correct way?
Try these queries:
SELECT col1, col2,col3,col4 FROM TABLE1 T1
WHERE (EXISTS (SELECT 1 FROM TABLE2 T2 WHERE T1.COL3 = T2.FIELD1)
OR COL4 IN ('A','B','C'))
SELECT col1, col2,col3,col4 FROM TABLE1 T1
WHERE EXISTS (SELECT 1 FROM TABLE2 T2 WHERE T1.COL3 = T2.FIELD1)
UNION
SELECT col1, col2,col3,col4 FROM TABLE1 T1 WHERE COL4 IN ('A','B','C')
Related
I would like to understand the easy/better way to join 2 tables with same characteristics and different measures as an example described below:
tab1
Col1
Col2
Measure1
1
1
10
1
2
5
tab2
Col1
Col2
Measure2
1
1
20
2
1
25
Expected Result
Col1
Col2
Measure1
Measure2
1
1
10
20
1
2
5
0
2
1
0
25
Questions:
How to avoid message: Ambiguous column name col1?
How to create a correct Join?
I have tried:
select col1, col2, t1.Measure1, t2.Measure2
from tab1 t1
full outer jon tab2 t2
on t1.col1 = t2.col1
and t1.col2 = t2.col2
I have tried a Union and it works, but i am looking a easy way using joins:
Select col1, col2, Measure1, 0 as Measure2 From tab1
Union
Select col1, col2, 0 as Measure1, Measure2 From tab2
The full join is the correct approach. But you need to disambiguate col1 and col2 in the select clause: both tables have both columns, so it is unclear to which column an unprefixed col1 refers.
A typical approach uses coalesce():
select
coalesce(t1.col1, t2.col1) col1,
coalesce(t1.col2, t2.col2) col2,
coalesce(t1.measure1, 0) measure1,
coalesce(t2.measure2, 0) measure2
from tab1 t1
full outer jon tab2 t2
on t1.col1 = t2.col1 and t1.col2 = t2.col2
Note that you also need coalesce() around the measures to return 0 instead of null on "missing" values.
In some databases (eg Postgres), you can use the using syntax to declare the join conditions for columns that have the same name across the tables ; this syntax automagically disambiguates the unprefixed column names, so:
select
col1,
col2,
coalesce(t1.measure1, 0) measure1,
coalesce(t2.measure2, 0) measure2
from tab1 t1
full join tab2 t2 using (col1, col2)
You should reference source tables for col1 and col2 as well.
As you're using FULL OUTER JOIN I'd recommend using COALESCE statement.
SELECT COALESCE(t1.col1, t2.col1) as col1,
COALESCE(t1.col2, t2.col2) as col2,
t1.Measure1,
t2.Measure2
FROM tab1 t1
FULL OUTER JOIN tab2 t2
on t1.col1 = t2.col1
and t1.col2 = t2.col2
I am having some trouble using a subquery for the IN clause of a query.
Hard-coding the IN .. values allows the query to execute quickly, but using a subquery slows everything down. Is there a way to speed this query up?
SELECT col1, col2, col3 FROM table1
WHERE ...
and col1 in (SELECT col1 FROM table2)
...
*The values for the IN clause will be a list of strings
SELECT col1, col2, col3 FROM table1
WHERE ...
and col1 in ('str1', 'str2', 'str3', ...)
...
The above works fine.
EDIT:
I think I was oversimplifying the problem. The query I am trying to execute looks like this:
SELECT col1, col2, col3, ...
FROM table1 t1, table2 t2
WHERE t1.col1 IN (SELECT col FROM table3)
and t1.col2 < 50
and t2.col3 = t1.col3
...
You cant write select * from . If you give select * from, it doesnot understand which column to compare with from table2. Use the column name you need.
SELECT * FROM table1
WHERE ...
and col1 in (SELECT col1 FROM table2)
...
Use JOIN instead,
and keep an index defined on table1.col1 or table2.col3 or table1.col3 or table3.col :
SELECT col1, col2, col3, ...
FROM table1 t1
INNER JOIN table2 t2 on ( t2.col3 = t1.col3 )
INNER JOIN table3 t3 on ( t1.col1 = t3.col )
WHERE t1.col2 < 50;
Never use commas in the FROM clause. Always use proper, explicit, standard JOIN syntax. You should write the query as:
SELECT col1, col2, col3, ...
FROM table1 t1 JOIN
table2 t2
ON t2.col3 = t1.col3
WHERE t1.col1 IN (SELECT col FROM table3) AND
t1.col2 < 50;
I would write this using EXISTS, rather than IN:
SELECT col1, col2, col3, ...
FROM table1 t1 JOIN
table2 t2
ON t2.col3 = t1.col3
WHERE EXISTS (SELECT 1 FROM table3 t3 WHERE t1.col1 = t3.col) AND
t1.col2 < 50;
The filtering is all on table1; however, the columns are being compared with inequalities. I would try the following indexes: table2(col3), table1(col2, col1), and table3(col).
We have a SQL query which is not written as per the sql guideline. We have to change the query but if we change the logic and remove the inner query then it take to much time to execute. Below is the query:
select col1,
col2,
case
when col1 <> '' then(select top 1
col1
from table1 as BP
where bp.col1 = FD.col1 order by BP.col1)
when col2 <> '' then(select top 1
BP.col2
from table1 as BP
where BP.col2 = FD.col2 order by BP.col2)
else ''
end
from table2 FD
The above query is being used to insert the data into a temp table. The table1 has almost 100 million of data. Is there any way to remove the inline query along with the good performance. We have already created the indexes on table1. Any thought?
Try this
;WITH CTE
AS
(
SELECT
RN = ROW_NUMBER() OVER(ORDER BY COALESCE(T2.col1,T2.col2)),
T2.col1,
T2.col2,
T1Val = COALESCE(T2.col1,T2.col2,'')
FROM table2 T2
LEFT JOIN table1 T1
ON
(
(
ISNULL(T2.col1,'')<>'' AND T1.col1 = T2.col1
)
OR
(
ISNULL(T2.col2,'')<>'' AND T1.col2 = T2.col2
)
)
)
SELECT
*
FROM CTE
WHERE RN = 1
Here is my modest help:
You can already prepare and materialize your subquery1 and subquery2 (Group BY col1 or col2) <-- It will reduce the size of your table 1)
Split your main query (from table2 into 3 different queries)
1 with SELECT .. FROM table2 WHERE col1 <> ''
1 with SELECT .. FROM table2 WHERE col1 = '' AND col2 <> ''
1 with SELECT .. FROM table2 WHERE col1 = '' AND col2 = ''
Use an INNER JOIN with your table created in the first point.
(If you use SSIS you can // and use your inner join table into a Lookup)
If your col1 or col2 use a NVARCHAR(MAX) or a big size, you should have a look to a HashFunction (MD5 for example) and compare Hash instead.
Be sure to have all your indexes
At least if it is not performant, you can try with:
OUTER APPLY (SELECT TOP 1 .. )
Another idea should be:
SELECT col1, col2, col1 AS yourNewCol
FROM table2 T2
WHERE EXISTS( SELECT 1 FROM table1 T1 WHERE T1.col1 = T2.col1)
UNION ALL
SELECT col1, col2, col2 AS yourNewCol
FROM table2 T2
WHERE
NOT EXISTS( SELECT 1 FROM table1 T1 WHERE T1.col1 = T2.col1)
AND EXISTS( SELECT 1 FROM table1 T1 WHERE T1.col2 = T2.col2)
UNION ALL
...
I don't have a clean solution for you, but some ideas.
Let me know if it helps you.
Regards,
Arnaud
I am trying to accomplish the following, and I am not sure if it is possible. I have a SELECT Statement that contains an inner SELECT for two of the table columns like so:
SELECT
col1,
col2,
(SELECT SUM(col1)
FROM table2)
AS FirstResultToAdd,
(SELECT SUM(col2)
FROM table3)
AS SecondResultToAdd,
FROM Table1
So my question is: Is it possible to perform a calculation, such as doing a SUM of "FirstResultToAdd" and "SecondResultToAdd, and returning that as a single column result on "Table1"? Also to keep in mind, I have excluded any joins of the tables to keep the example simple.
I believe you want to perform some logic on the result of Sub-query
To add the two sub-query result
SELECT col1,
col2,
(SELECT col1
FROM table2)
AS FirstResultToAdd,
(SELECT col2
FROM table3)
AS SecondResultToAdd,
(SELECT col1
FROM table2)
+
(SELECT col2
FROM table3)
AS total
FROM table1
To make the query more readable you can make the original query as Sub-Select and perform the logic in Outer query
just nest one more time...
select col1, col2, sum( FirstResultToAdd )
from (
SELECT
col1,
col2,
(SELECT col1
FROM table2)
AS FirstResultToAdd,
(SELECT col2
FROM table3)
AS SecondResultToAdd,
FROM Table1
)
Edit: Fixed Group By
Try this:
Select A.Col1,
A.Col2,
(B.Col3 + C.Col4)
From(
(Select Col1,
Col2
From [Table1]) A
Inner join (Select Sum(Col3) AS Col3
From [Table2]) B on 1 = 1
Inner join (Select Sum(Col4) AS Col4
From [Table3]) C on 1 = 1
)
Group By A.Col1,
A.Col2,
B.Col3,
C.Col4
How to get the following join
input:
table1: table2:
col1 Col1 col2 col3
A A 1 2
B B 4 5
C
output:
col1 col2 col3
A 1 2
B 4 5
c - -
SELECT t1.col1, t2.col2, t2.col3
FROM table1 t1
LEFT JOIN table2 t2 ON t1.col1=t2.col1
;
You can do this using full outer join:
select coalesce(t1.col1, t2.col1), t2.col2, t2.col3
from table1 t1 full outer join
table2 t2
on t1.col1 = t2.col1;
This returns all rows from both tables, even those that don't match (it is a left and right outer join at the same time).
You can also do this using union all and aggregation:
select col1, max(col2) as col2, max(col3) as col3
from ((select col1, NULL as col2, NULL as col3
from table1
) union all
(select col1, col2, col3
from table2
)
) t
group by col1;
select t1.col1, t2.col2, t2.col3
from table1 t1
left outer join table2 t2
on t1.col1 = t2.col1
Maybe something like this if you wan't the '-'
SELECT t1.col1, coalesce(t2.col2,'-') as col2, coalesce(t2.col3,'-') as col3
FROM table1 t1
LEFT JOIN table2 t2 ON t1.col1=t2.col1
See my sqlfiddle
create table table1(
col1 char(1)
);
insert into table1 values('A');
insert into table1 values('B');
insert into table1 values('C');
create table table2(
col1 char(1),
col2 int,
col3 int
);
insert into table2 values('A',1,2);
insert into table2 values('B',4,5);
select
t1.col1,
coalesce(t2.col2,'-'),
coalesce(t2.col3,'-')
from
table1 t1
left join table2 t2 on t1.col1=t2.col1
;
http://sqlfiddle.com/#!2/bc768/2
You need to do an outer join
SELECT *
FROM table1 t1,
table2 t2
WHERE t1.col1 = t2.col1(+)