How can I write WHERE cluase so it returns rows that meet the criteria, if there are no such records it should return all records from a table?
Using UNION ALL:
select t.* from table t where condition
union all
select t.* from table t cross join (select count(*) cnt from table where condition) c
where c.cnt=0
Or (much more efficiently):
select col1, col2, ... colN
from
(
select t.*, sum(case when condition then 1 else 0 end) over() cnt from table
) s
where condition or s.cnt=0
Replace condition with your WHERE condition
One method you could consider in t-sql is to use ##rowcount to determine if you need to return all rows.
The benefit of doing so is you get two separate execution plans, one only optimised for your first exists criteria and would be beneficial if the majority of results are where the exists condition is met.
select <columns>
from <table>
where <condition>
if ##rowcount=0
begin
select <columns>
from <table>
end
One way would be:
SELECT *
FROM Person
WHERE
Name = 'John'
OR NOT EXISTS(SELECT null FROM Person WHERE Name = 'John')
I don't like it, for all those good reasons mentioned in the comments. If I was handed this requirement as part of a system I was creating I'd probably examine the need for the requirement; selecting all rows from a table is seldom useful if it's the sort of table that you query with a criteria: "Dear user, we couldn't find your person named John so here are the other 4.27 billion users in the system, pagination size 100"
that satisfies me enough:
WHERE (
ISNULL(#variable, '') = ''
OR #variable = [Column]
)
Not exactly what I described above but it returns all the records if condition is not met. However in that case condition would be assigning a value to variable.
1st method
Where ( ISNULL(#Param,'')='' OR ColumnName = #Param)
2nd way
WHERE ( ColumnName =CASE WHEN #Param IS NULL THEN ColumnName
ELSE #Param
END)
3rd way
WHERE (#Param ='' OR #Param =ColumnName)
I would recommend a CTE with not exists:
with cte as (
select t.*
from t
where . . .
)
select *
from cte
union all
select *
from t
where not exists (select 1 from cte);
I need to get a maximum of 3 distinct records from the same table, so currently I'm doing:
SELECT 1, mycolumn FROM mytable WHERE id = #firstId
UNION ALL
SELECT 2, mycolumn FROM mytable WHERE id = #secondId
UNION ALL
SELECT 3, mycolumn FROM mytable WHERE id = #thirdId
The actual SELECT part contains over 20 columns and the FROM part contains a number of JOINs. The first column is a constant and is always fixed depending on the record. I don't know how many records might return. It could be anything from 0 to 3 records.
Is it possible to change the above query so that it uses IN like this:
SELECT ???, mycolumn FROM mytable WHERE id IN (#firstId, #secondId, #thirdId)
But how do I explicitly map each record to the fixed constant if I use IN?
You may use a CASE expression here with a single query:
SELECT
CASE id WHEN #firstId THEN 1
WHEN #secondId THEN 2
WHEN #thirdId THEN 3 END AS val,
mycolumn
FROM mytable
WHERE
id IN (#firstId, #secondId, #thirdId);
If you wish to also order by the computed column, then add ORDER BY val to the end of the above query.
You can use CASE like following.
SELECT
CASE
WHEN id= #firstId THEN 1
WHEN id=#secondId THEN 2
ELSE 3
END AS rn,
mycolumn
FROM mytable
WHERE id IN (#firstId,
#secondId,
#thirdId)
Another approach can be using DENSE_RANK if you have one record for each provided id and #firstId, #secondId & #thirdId are in ascending order.
SELECT DENSE_RANK()
OVER(
ORDER BY id) rn,
mycolumn
FROM mytable
WHERE id IN ( #firstId, #secondId, #thirdId )
I would recommend a table-valued constructor for this purpose:
select v.outputnum, my_column
from mytable t join
(values (#firstid, 1),
(#secondid, 2),
(#thirdid, 3)
) v(id, outputnum)
on t.id = v.id
order by v.outputnum;
I think this is simpler than other versions, because the list of ids is only present once in the query -- so no danger of different parts of the query getting out of sync.
I've been staring at this for hours and hours and can't come up with an "elegant" set-based way of getting the result set I need...
Here's my sample data (my real data could be 1,000,000+ rows)...
DECLARE #t AS TABLE (ID int,ID1 nvarchar(15),[DATE] date,PERIOD int,[TYPE] nchar(1));
INSERT INTO #t (ID,ID1,[DATE],PERIOD,[TYPE])
VALUES
(1,N'NUM1','2016-01-01',1,N'B'),
(2,N'NUM1','2016-01-01',2,N'A'),
(3,N'NUM1','2016-01-01',3,N'A'),
(4,N'NUM1','2016-01-01',4,N'B'),
(5,N'NUM1','2016-01-01',4,N'A'),
(6,N'NUM1','2016-01-01',5,N'A'),
(7,N'NUM1','2016-01-02',1,N'A'),
(8,N'NUM1','2016-01-02',2,N'A'),
(9,N'NUM1','2016-01-02',3,N'A'),
(10,N'NUM1','2016-01-02',4,N'A'),
(11,N'NUM1','2016-01-02',5,N'A'),
(12,N'NUM2','2016-01-01',1,N'A'),
(13,N'NUM2','2016-01-01',1,N'B'),
(14,N'NUM2','2016-01-01',2,N'A'),
(15,N'NUM2','2016-01-01',3,N'A'),
(16,N'NUM2','2016-01-01',4,N'B'),
(17,N'NUM2','2016-01-01',4,N'A'),
(18,N'NUM2','2016-01-01',5,N'A'),
(19,N'NUM2','2016-01-02',1,N'A'),
(20,N'NUM2','2016-01-02',2,N'B'),
(21,N'NUM2','2016-01-02',3,N'A'),
(22,N'NUM2','2016-01-02',4,N'A'),
(23,N'NUM2','2016-01-02',4,N'B'),
(24,N'NUM2','2016-01-02',5,N'A');
Here is the result set I'm trying to get...
1,'NUM1','2016-01-01',1,'B'
2,'NUM1','2016-01-01',2,'A'
3,'NUM1','2016-01-01',3,'A'
5,'NUM1','2016-01-01',4,'A'
6,'NUM1','2016-01-01',5,'A'
7,'NUM1','2016-01-02',1,'A'
8,'NUM1','2016-01-02',2,'A'
9,'NUM1','2016-01-02',3,'A'
10,'NUM1','2016-01-02',4,'A'
11,'NUM1','2016-01-02',5,'A'
12,'NUM2','2016-01-01',1,'A'
14,'NUM2','2016-01-01',2,'A'
15,'NUM2','2016-01-01',3,'A'
17,'NUM2','2016-01-01',4,'A'
18,'NUM2','2016-01-01',5,'A'
19,'NUM2','2016-01-02',1,'A'
20,'NUM2','2016-01-02',2,'B'
21,'NUM2','2016-01-02',3,'A'
22,'NUM2','2016-01-02',4,'A'
24,'NUM2','2016-01-02',5,'A'
Simply put, each day has 5 periods. They can be of type A or B. I need to get the A types. but if there are no A types, I need to get the B types... (Sounds so simple when I write it out.., but my brain will not come up with something suitable)
Pleeeeeease put me out of my misery..
You can use ROW_NUMBER for this:
SELECT ID, ID1, [DATE], PERIOD, [TYPE]
FROM (
SELECT ID, ID1, [DATE], PERIOD, [TYPE],
ROW_NUMBER() OVER (PARTITION BY ID1, [DATE], PERIOD
ORDER BY [TYPE]) AS rn
FROM #t) AS t
WHERE t.rn = 1
Using ORDER BY [TYPE] in the OVER clause of ROW_NUMBER places 'A' records on top of 'B' records. If there are no 'A' records for a given ID1, [DATE], PERIOD then B records are assigned rn = 1.
Your desired outpout contradicts the statement that "I need to get the A types. but if there are no A types, I need to get the B types... ". Every date in the data has one or more 'A' types. By the statement, the output should include only the 'A' types. But if the statement is correct, then this should work:
Select d.[DATE], t.Id, t.ID1, t.PERIOD, t.[TYPE]
from (select distinct [date] from #t) d
left join #t t
on t.[date] = d.[date]
and t.type = case when exists
(select * from #t
where [date] = d.[Date]
and type = 'A') then 'A'
else 'B' End
I've just come up with
SELECT * FROM #t WHERE [TYPE]='A'
UNION ALL
SELECT * FROM #t t1 WHERE [TYPE]='B' AND NOT EXISTS (SELECT ID FROM #t WHERE ID1=t1.ID1 AND [TYPE]='A' AND [DATE]=t1.[DATE] AND Period=t1.Period)
ORDER BY ID;
which give's me what I need...
i need your help to insert into from select but my query is too complex for me. My logic is below
INSERT INTO TheTable(A,CustomerNo,item,B,C,D)
SELECT DISTINCT
case when ((select count(*) from hesap where CustomerNo=e.CustomerNo)0) then
select top 1, A,CustomerNo,item+1,B,C,D
from dbo.Table1 order by ekno desc
) else select 100,e.CustomerNo,e.item,0,e.defterid,'C'
from Table2 e end
But i can not do that...
You can do case on column basis only.
What you can do is UNIONing two selects, and insert the result. Something like
INSERT INTO TheTable(A,CustomerNo,item,B,C,D)
SELECT ...
WHERE (select count(*) from hesap where CustomerNo=e.CustomerNo) = 0
UNION
SELECT select 100,e.CustomerNo,e.item,0,e.defterid,'C'
WHERE (select count(*) from hesap where CustomerNo=e.CustomerNo) > 0
I'm sorry, I cannot always follow your Select, but I hope you got the idea. You have to separate the 2 possibilities before you UNION them, so only 1 row can exist for each original row.
Can you try removing the comma after top 1 Like this:
INSERT INTO TheTable(A,CustomerNo,item,B,C,D)
SELECT DISTINCT
case when ((select count(*) from hesap where CustomerNo=e.CustomerNo)0) then
select top(1) A,CustomerNo,item+1,B,C,D
from dbo.Table1 order by ekno desc
)
else select 100,e.CustomerNo,e.item,0,e.defterid,'C'
from Table2 e end
In Microsoft SQL Server 2005 or above, I would like to get the first row, and if there is no matching row, then return a row with default values.
SELECT TOP 1 ID,Name
FROM TableName
UNION ALL
SELECT 0,''
ORDER BY ID DESC
This works, except that it returns two rows if there is data in the table, and 1 row if not.
I'd like it to always return 1 row.
I think it has something to do with EXISTS, but I'm not sure.
It would be something like:
SELECT TOP 1 * FROM Contact
WHERE EXISTS(select * from contact)
But if not EXISTS, then SELECT 0,''
What happens when the table is very full and you might want to specify which row of your top 1 to get, such as the first name? OMG Ponies' query will return the wrong answer in that case if you just change the ORDER BY clause. His query also costs about 8% more CPU than this modification (though it has equal reads)
SELECT TOP 1 *
FROM (
SELECT TOP 1 ID,Name
FROM TableName
ORDER BY Name
UNION ALL
SELECT 0,''
) X
ORDER BY ID DESC
The difference is that the inner query has a TOP 1 also, and which TOP 1 can be specified there (as shown).
Just for fun, this is another way to do it which performs very closely to the above query (-15ms to +30ms). While it's more complicated than necessary for such a simple query, it demonstrates a technique that I don't see other SQL folks using very often.
SELECT
ID = Coalesce(T.ID, 0),
Name = Coalesce(T.Name, '')
FROM
(SELECT 1) X (Num)
LEFT JOIN (
SELECT TOP 1 ID, Name
FROM TableName
ORDER BY ID DESC
) T ON 1 = 1 -- effective cross join but does not limit rows in the first table
Use:
SELECT TOP 1
x.id,
x.name
FROM (SELECT t.id,
t.name
FROM TABLENAME t
UNION ALL
SELECT 0,
'') x
ORDER BY id DESC
Using a CTE equivalent:
WITH query AS (
SELECT t.id,
t.name
FROM TABLENAME t
UNION ALL
SELECT 0,
'')
SELECT TOP 1
x.id,
x.name
FROM query x
ORDER BY x.id DESC
CREATE TABLE #sample(id INT, data VARCHAR(10))
SELECT TOP 1 id, data INTO #temp FROM #sample
IF ##ROWCOUNT = 0 INSERT INTO #temp VALUES (null, null)
SELECT * FROM #temp
put the top oustide of the UNION query
SELECT TOP 1 * FROM(
SELECT ID,Name
FROM TableName
UNION ALL
SELECT 0,''
) z
ORDER BY ID DESC
IF EXISTS ( SELECT TOP 1 ID, Name FROM TableName )
BEGIN
SELECT TOP 1 ID, Name FROM TableName
END
ELSE
BEGIN
--exists returned no rows
--send a default row
SELECT 0, ''
END