I've got a SQL question. I want to use case logic to determine the value of an ad hoc column based on the result of comparisons done in the where clause. Simplified, I want to do something like this:
select t.id,
(case
when cond1 then "lbl1" + t2.v1
when cond2 then "lbl2" + t2.v1)
from
tbl1 as t left join tbl2 as t2
where
( cond1 || cond2 )
The problem is I don't want to recompute cond1 and cond2 in the select clause, as they're expensive.
How can I get this result?
Thanks,
frood
This was written in MS SQL 2008, not sure if it'll work in other RDBMS with the same code, but hopefully it gives you an idea of what might work. it would have to be iterated for each record, but overall would have to run each comparison once instead of twice for each record.
declare #cond1 as bit
declare #cond2 as bit
if 1=1 -- substitute with condition 1
set #cond1 = 1
ELSE
set #cond1 = 0
if 1=0 -- substitute with conditon 2
set #cond2 = 1
ELSE
set #cond2 = 0
SELECT
CASE WHEN #Cond1 = 1 THEN 'Condition 1 met'
WHEN #Cond2 = 1 THEN 'Condition 2 met'
END
WHERE #cond1 = 1 OR #cond2 = 1
Related
DECLARE #Todaydate DATE
SET #Todaydate = '12/31/2017'
SELECT
CASE
WHEN DATEDIFF(dd,#Todaydate,getdate()) >= 31
THEN (SELECT a.CU, , b.abc
FROM histhold a, security b
WHERE T_QUANTITY_P <> 0
AND ACCOUNTING_DATE = '04/30/2018'
AND a.cu = b.CU)
ELSE ''
END
Just do the logic in the WHERE clause:
SELECT a.CU, , b.abc
FROM histhold a
INNER JOIN security b
ON a.cu = b.CU
WHERE T_QUANTITY_P <> 0
AND ACCOUNTING_DATE = '04/30/2018'
AND DATEDIFF(dd,#Todaydate,getdate()) >= 31;
Unless this is part of some larger procedure/script I can't imagine a reason why you would only want to execute a query given certain conditions (as opposed to executing the query and restricting the results based on those conditions potentially returning an empty recordset).
I am deriving a CTE using data from 2 tables, and I have a requirement to update 2 columns in this CTE. The I can use UPADTE CTE and then a case statement to update one column, but the second one.
for example
update cte
set col1 = case when thisrecord = thatrecord then 1 else 0 end
col2 = case max(thisrecord) = max(thatrecord) then 1 else 0 end
It gives me error.
If I use
update cte
set col1, set col2
from cte
where this = that
then it says cte is not updatable as it has multiple base tables.
How to solve this puzzle, does anyone has a similar scenario or possible work out?
I am doing a exercise
I'll fire a query on the DB and get some 500 results. Now i want to sort this list based on some conditions and present the sorted list in client side.
I am using Java/Java EE and MySQL server 5.5
Conditions are like this,
Example: Consider a table having listed with cars
So, i ll fire a query on the table and it will list some 500 cars. now i want to sort this list based on user criteria.
conditions are age of car, colour of car and facilities of cars. List should be sorted like this
First appears the list of cars which satisfies all three conditions ie., same age as mentioned by end user, same colour and with all facilities user selected.
Second appears any 2 conditions satisfying cars list and one condition not satifying.
Third appears any one condition satisfying cars list and not the other two.
And finally appears the list of cars of which no conditions are satisfied.
How can i achieve this. I have searched in google, asked in irc channels regarding this. Couldn't get any help.
I have tried using RANK function by defining the CASES and finally order by RANK. It works for me while the conditions fields (columns) are of same table. In my case the fields are from a parent table as well as its child tables which has many to one relationship with its parent. Like in this example, age and color of the cars are stored in parent table and facilities that cars has are stored in another table. I tried doing the same using inner join, but no luck.
I tried something like this:
Query:
select distinct t0.id,t0.name,t0.price,
CASE
WHEN
t1.age='2' AND t1.colour='Red' AND t2.facilities_id=9 THEN 1
WHEN
t1.age='2' AND t1.colour='Red' AND t2.facilities_id!=9 THEN 2
WHEN
t1.age='2' AND t1.colour!='Red' AND t2.facilities_id=9 THEN 3
WHEN
t1.age!='2' AND t1.colour='Red' AND t2.facilities_id=9 THEN 4
WHEN
t1.age!='2' AND t1.colour='Red' AND t2.facilities_id!=9 THEN 5
WHEN
t1.age='2' AND t1.colour!='Red' AND t2.facilities_id!=9 THEN 6
WHEN *
t1.age!='2' AND t1.colour!='Red' AND t2.facilities_id=9 THEN 7
ELSE 8
END as pre_status
from cars_listing t0
inner join
cars_listing_details t1
on t0.id=t1.mg_listing_id
inner join
cars_facilities_listing t2
on t1.cars_listing_id=t2.listing_id
where t0.type='new_cars'
order by pre_status
Thanks in advance for helping.
try ordering by something like...
order by
case when first_condition then 1 else 0 end
+ case when second_condition then 1 else 0 end
+ case when third_condition then 1 else 0 end DESC
select distinct
t0.id,
t0.name,
t0.price,
case when t1.age = '2' then 1 else 0 end as MatchedAge,
case when t1.colour='Red' then 1 else 0 end as MatchedColor,
case when t2.facilities_id = 9 THEN 1 else 0 end as MatchedFacility
from
cars_listing t0
inner join cars_listing_details t1
on t0.id = t1.mg_listing_id
inner join cars_facilities_listing t2
on t1.cars_listing_id = t2.listing_id
where
t0.type = 'new_cars'
order by
case when t1.age = '2' then 1 else 0 end
+ case when t1.colour='Red' then 1 else 0 end
+ case when t2.facilities_id = 9 THEN 1 else 0 end DESC
If one field is a higher priority -- such as a red car, you could even give that more weight than the other in the order by... So a Red car at Facility 5 would show before a Blue car at facility 9 just by changing the order by to something like
order by
case when t1.age = '2' then 1 else 0 end
+ case when t1.colour='Red' then 5 else 0 end <-- applyi higher Wgt to color match vs other criteria
+ case when t2.facilities_id = 9 THEN 1 else 0 end DESC
Well, I have done Dynamic sql where condition in my project. It might help you. I have created a stored procedure for SELECT query. (I have done it in SQL Server 2008 R2). Tell me if you need more help.
USE [DATABASE_NAME]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE PROCEDURE [dbo].[PROCEDURE_NAME]
#Id int = NULL,
#Requester varchar(20) = NULL,
#Suggester varchar(20) = NULL
AS
BEGIN
DECLARE #sql nvarchar(4000)
SELECT #sql='SELECT Id, Suggester, Requester from DATABASE_NAME.dbo.TABLE_NAME WHERE 1=1 '
If (#Id) IS NOT NULL
SELECT #sql=#sql + ' AND Id=(#Id) '
If (#Suggester) IS NOT NULL
SELECT #sql=#sql + ' AND Suggester like (#Suggester) '
If (#Requester) IS NOT NULL
SELECT #sql=#sql + ' AND Requester like (#Requester) '
EXEC sp_executesql #sql, N'#id int, #Requester varchar(20), #Suggester varchar(20)',
#Id, #Requester, #Suggester
END
GO
Here in this SP; Id,Requester,Suggester are field names.
I apologize for asking a very vague question but here it is.
I have to write a SQL query in SQL Server as follows.
I have a table say tblA having 10 columns from col1, col2,.....col10.
Each column is not null and definitely holds some value and all of type int.
The query should be to select all such records in which at least 4 columns are matching with given filter criteria, where the filter criteria has values for all 10 columns.
I googled dint get a clue. It needs to be done in SQL server and single query.
Please suggest.
Thanks in advance.
SELECT *
FROM
yourtable
WHERE
case col1 when #value1 then 1 else 0 end +
case col2 when #value2 then 1 else 0 end +
...
case col10 when #value10 then 1 else 0 end
>=4
You can use CASE expressions to determine if four or more columns match:
SELECT *
FROM YourTable
WHERE CASE WHEN Col1 = Filter1 THEN 1 ELSE 0 END +
CASE WHEN Col2 = Filter2 THEN 1 ELSE 0 END +
....
CASE WHEN Col10 = Filter10 THEN 1 ELSE 0 END >= 4
You can do something like this:
select *
from (select t.*,
(case when col1 <whatever> then 1 else 0 end) as col01_matches,
(case when col2 <whatever> then 1 else 0 end) as col02_matches,
. . .
from t
) t
where (col1_matches + col2_matches + col3_matches . . .) >= 4
This creates a separate indicator variable for each match. You could also do the sum in the subquery, in a single variable. I would prefer to have each match separately, just in case the logic gets more complicated or I want to see what matches.
I'm trying to create a query that would generate a cross-check table with about 40 custom columns that show Y or N. Right now I have
SELECT DISTINCT [Company],
[Option1],
[Option2],
[Option3],
CASE
WHEN [Table1].[ID1] IN (SELECT ID2 FROM Table2 WHERE Variable = 1 AND Bit = 1) THEN
'Y'
ELSE 'N'
END AS 'CustomColumn1:',
CASE
WHEN [Table1].[ID1] IN (SELECT ID2 FROM Table2 WHERE Variable = 2 AND Bit = 1) THEN
'Y'
ELSE 'N'
END AS 'CustomColumn1:',
CASE
WHEN [Table1].[ID1] IN (SELECT ID2 FROM Table2 WHERE Variable = 3 AND Bit = 1) THEN
'Y'
ELSE 'N'
END AS 'CustomColumn1:',
.............
-- REPEAT ANOTHER 40 times
FROM [Table1]
WHERE [Table1].[OtherCondition] = 'True'
ORDER BY [Company]
So my question is, how do I create a loop (while? for?) that will loop on variable and assign Y or N to the row based on the condition, rather than creating 40+ Case statements?
You couldn't use a loop, but you could create a stored procedure/function to perform the sub-select and case expression and call that 40 times.
Also, you could improve performance of the sub-select by changing it to
SELECT 1 FROM Table2 WHERE EXISTS [Table2].[ID2] = [Table1.ID1] AND Variable = 3 AND Bit = 1
A loop (that is, iterating through a cursor) works on rows, not columns. You will still have to have 40 expressions, one for each column, and the performance will be terrible.
Let SQL Server do its job. And do your bit by telling exactly what you need and creating proper indices. That is, replace
CASE WHEN [Table1].[ID1] IN (SELECT ID2 FROM Table2 WHERE Variable = 2 AND Bit = 1)
with
CASE WHEN EXISTS (SELECT 0 FROM Table2 WHERE ID2 = [Table1].[ID1] AND Variable = 2 AND Bit = 1)
If the output is so vastly different than the schema, there is a question as to whether the schema properly models the business requirements. That said, I would recommend just writing the SQL. You can simplify the SQL like so:
Select Company
, Option1, Option2, Option3
, Case When T2.Variable = 1 Then 'Y' Else 'N' End As CustomCol1
, Case When T2.Variable = 2 Then 'Y' Else 'N' End As CustomCol2
, Case When T2.Variable = 3 Then 'Y' Else 'N' End As CustomCol3
, Case When T2.Variable = 4 Then 'Y' Else 'N' End As CustomCol4
...
From Table1 As T1
Left Join Table2 As T2
On T2.ID2 = T1.ID
And T2.Bit = 1
Where T1.OtherCondition = 'True'
Group By T1.Company
Order By T1.Company
If you want to write something that can help you auto-gen those Case statements (and you are using SQL Server 2005+), you could do something like:
With Numbers As
(
Select 0 As Value
Union All
Select Value + 1
From Numbers
Where Value < 41
)
Select ', Case When T2.Variable = ' + Cast(N.Value As varchar(10)) + ' Then ''Y'' Else ''N'' End As CustomCol' + Cast(N.Value As varchar(10))
From Numbers As N
You would run the query and copy and paste the results into your procedure or code.
One way could have been to use Pivot statement, which is in MS SQL 2005+. But even in that you have to put 1 ... 40 hardcoded columns in pivot statement.
Other way i can think of is to create dynamic SQL, but it is not so much recommended, So what we can do is we can create a dynamic sql query by running a while loop on table and can create the big sql and then we can execute it by using sp_execute. So steps would be.
int #loopVar
SET #loopVar = 0
int #rowCount
varchar #SQL
SET #SQl = ''
Select #rowcount = Count(ID2) from Table2
WHILE(#loopVar <= #rowCount)
BEGIN
// create ur SQL here
END
sp_execute(#SQL)