I have two queries, query1 and query2. What I would like to do is, if returned rows of query1 is empty, return query2 instead. Is that possible using basic SQL query alone? They have same returning columns btw, but different table sources.
eg:
query1:
SELECT name, message
FROM table1
query2:
SELECT name, message
FROM table 2
If query1 is empty, return name, message from query2.
This will select from table1 if not empty, otherwise select from table2:
SELECT * FROM table1
WHERE EXISTS (select * from table1)
UNION ALL
SELECT * FROM table2
WHERE NOT EXISTS (select * from table1)
This checks if table1 has no rows:
EXISTS (SELECT * FROM TABLE)
Found an answer here: https://stackoverflow.com/a/25122516/3747493
Basically:
SELECT *
FROM table1
UNION ALL
SELECT *
FROM table2
WHERE (SELECT COUNT(*) FROM table1) = 0
Thanks guys!
Related
I am trying to create a union with 3 tables that have the same column names. However, the queries tested seems not to be working.
The first query that I have used is the following:
Select * FROM table1
UNION ALL
SELECT * FROM table2
SELECT * FROM table3
UNION ALL
The second query used is the following:
SELECT *
FROM
(select * from table_1),
(select * from table_2),
(select * from table_3)
Both of them are not working for me. Please someone can help me with this?
This should work if columns are identical:
SELECT * FROM table1 UNION ALL
SELECT * FROM table2 UNION ALL
SELECT * FROM table3
I need to select all id + 1 and id - 1 row information from MYTABLE with condition that id exist in existing query on same table .
I tried:
SELECT *
FROM MYTABLE
WHERE
id - 1 IN (SELECT * FROM MYTABLE WHERE EXISTINGQUERY) AND
id + 1 IN (SELECT * FROM MYTABLE WHERE EXISTINGQUERY)
But it doesn't work.
Any suggestions?
It seems to me you may write your query by using join like below
SELECT t1.* FROM MYTABLE t1
join (SELECT * FROM MYTABLE WHERE EXISTINGQUERY) t2
on (t1.id-1=t2.id or t1.id+1=t2.id)
The following SELECT statement may be used that includes the substitution variable :id
SELECT s.*
FROM MYTABLE s
WHERE id in (:id - 1,:id + 1)
AND EXISTS ( SELECT 1 FROM MYTABLE s WHERE id =:id AND EXISTINGQUERY);
where colon(:) notation may be replaced with # or & depending on the database.
I need to return the unique records between two tables. Ideally, an UNION would solve my problem but both tables contain an object field which gives me an error(cannot ORDER objects without MAP or ORDER method) when I do UNION/distinct.
So, I was wondering if I can do a UNION ALL(to avoid the error) to get all the records first then do something to return only the unique records from there. I tried analytic function combined with the UNION ALL query but no luck so far.
Select * from Table1
union all
Select * from table2
Any help? Note:I need to return all fields.
I actually solved the problem using analytic function+row_num. The query will choose the first record for each set of duplicates hence returning only the unique records.
select * from
(
select ua.*,row_number() over (partition by p_id order by p_id ) row_num from
(
select * from table1
union all
select * from table2
)ua
) inner
where inner.row_num=1
How about this :
SELECT DISTINCT A.* FROM
(
Select * from Table1
union all
Select * from table2
) A;
(or)
SELECT col1,col2,col3...coln FROM
(
Select col1,col2,col3...coln from Table1
union all
Select col1,col2,col3...coln from table2
) A
GROUP BY A.col1,col2,col3...coln;
UNION ALL will give duplicate values as well .. instead use UNION and see if you are facing the error
I need to count rows in more than one table in SQL Server 2008. I do this:
select count(*) from (select * from tbl1 union all select * from tbl2)
But it gives me an error of incorrect syntax near ). Why?
PS. The actual number of tables can be more than 2.
In case you have different number of columns in your tables try this way
SELECT count(*)
FROM (
SELECT NULL as columnName
FROM tbl1
UNION ALL
SELECT NULL
FROM tbl2
) T
try this:
You have to give a name to your derived table
select count(*) from
(select * from tbl1 union all select * from tbl2)a
I think you have to alias the SELECT in the FROM clause:
select count(*)
from
(
select * from tbl1
union all
select * from tbl2
) AS SUB
You also need to ensure that the * in both tables tbl1 and tbl2 return exactly the same number of columns and they have to be matched in their type.
I don't like doing the union before doing the count. It gives the SQL optimizer an opportunithy to choose to do more work.
AlexK's (deleted) solution is fine. You could also do:
select (select count(*) from tbl1) + (select count(*) from tbl2) as cnt
I don't know it may sound weird... but here is my situation... I have to select rows from two tables (Table1) and (Table2)
Select * from Table1 Where <SomeCondition>
Select * from Table2 Where <SomeCondition>
But my constraint is If Table1 / Table2 return 0(zero) Rows... I should not return any results at all.
That ie... If 1st select returns say 10 rows and the 2nd select returns 0 (zero) rows, I should call back the first select also...
Is the Temp tables the only solution, or do we have any other alternative.
Thanks in advance for your response...
Raja
One approach is to do an IF EXISTS first:
IF EXISTS(SELECT * FROM Table1 WHERE....) AND EXISTS(SELECT * FROM Table2 WHERE....)
BEGIN
-- Now do your SELECT on each, as both return results
END
EXISTS should give good performance, as it will stop as soon as it does find a matching record.
Without more details of your specific queries, here is an option. As long as your queries aren't too complex aren't very intensive, this should work:
Select * from Table1 Where <SomeCondition>
where exists( Select null from Table2 Where <SomeCondition> );
Select null from Table2 Where <SomeCondition>
where exists ( Select null from Table1 Where <SomeCondition> );
This will only select rows in each statement if the other statement will also return any number of rows greater than zero.
An obvious but not-so-performant solution will be to count number of rows first (not sure about the syntax):
if not exists(select id from Table1 where ...) or not exists(select id from Table1 where ...)
return
Select * from Table1 Where <SomeCondition>
Select * from Table2 Where <SomeCondition>
If you can use stored procedures you can use ##rowcount to check if the second query returned any results:
create proc pTest
as
Select * from Table1 Where <SomeCondition>
Select * from Table2 Where <SomeCondition>
if ##rowcount = 0 return
go