Lets take two result sets as in: 1,2,3,5,7 and 2,4,6,7,8
In the end I want 1,2,3,4,5,6,7,8. I can not figure out how to code this in sql. Can any one give me some suggestions? I've seen some merging functions out there but having trouble implementing something simple.
You may use UNION
(SELECT id FROM table1 WHERE 1=1)
UNION
(SELECT id FROM table2 WHERE 1=1)
ORDER BY id
I think maybe you're thinking of UNION?
If SELECT `Column` FROM `Table` yields 1,2,3,5,7
And SELECT `Column` FROM `Table2` yields 2,4,6,7,8
Then
SELECT `Column` FROM `Table`
UNION
SELECT `Column` FROM `Table2`
yields 1,2,3,4,5,6,7,8
Related
I noticed that in PostgreSQL the following two queries output different results:
select a.*
from (
select distinct on (t1.col1)
t1.*
from t1
order by t1.col1, t1.col2
) a
where a.col3 = value
;
create table temp as
select distinct on (t1.col1)
t1.*
from t1
order by t1.col1, t1.col2
;
select temp.*
from temp
where temp.col3 = value
;
I guess it has something to do with using distinct on in subqueries.
What is the correct way to use distinct on in subqueries? E.g. can I use it if I don't use where statement?
Or in queries like
(
select distinct on (a.col1)
a.*
from a
)
union
(
select distinct on (b.col1)
b.*
from b
)
In normal situation, both examples should return the same result.
I suspect that you are getting different results because the order by clause of your distinct on subquery is not deterministic. That is, there may be several rows in t1 sharing the same col1 and col2.
If the columns in the order by do not uniquely identify each row, then the database has to make its own decision about which row will be retained in the resultset: as a consequence, the results are not stable, meaning that consecutive executions of the same query may yield different results.
Make sure that your order by clause is deterministic (for example by adding more columns in the clause), and this problem should not arise anymore.
I'm working on learning more about how the UNION function works in SQL Server.
I've got a query that is directed at a single table:
SELECT Category, COUNT(*) AS Number
FROM Table1
GROUP BY Category;
This returns the number of entries for each distinct line in the Category column.
I have multiple tables that are organized by this Category column and I'd like to be able to have the results for every table returned by one query.
It seems like UNION will accomplish what I want it to do but the way I've tried implementing the query doesn't work with COUNT(*).
SELECT *
FROM (SELECT Table1.Category
Table1.COUNT(*) AS Number
FROM dbo.Table1
UNION
SELECT Table2.Category
Table2.COUNT(*) AS Number
FROM dbo.Table2) AS a
GROUP BY a.Category
I'm sure there's an obvious reason why this doesn't work but can anyone point out what that is and how I could accomplish what I'm trying to do?
You cannot write a common Group by clause for two different select's. You need to use Group by clause for each select
SELECT TABLE1.Category, --missing comma here
COUNT(*) as Number -- Remove TABLE1. alias name
FROM dbo.TABLE1
GROUP BY Category
UNION ALL --UNION
SELECT TABLE2.Category, --missing comma here
COUNT(*) as Number -- Remove TABLE1. alias name
FROM dbo.TABLE2
GROUP BY Category
If you really want to remove duplicates in result then change UNION ALL to UNION
COUNT as any associated aggregation function has to have GROUP BY specified. You have to use group by for each sub query separately:
SELECT * FROM (
SELECT TABLE1.Category,
COUNT(*) as Number
FROM dbo.TABLE1
GROUP BY TABLE1.Category
UNION ALL
SELECT TABLE2.Category,
COUNT(*) as Number
FROM dbo.TABLE2
GROUP BY TABLE2.Category
) as a
It is better to use UNION ALL vs UNION - UNION eliminates duplicates from result sets, since - let say - you want to merge both results as they are it is safer to use UNION ALL
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 am retuning table results for different queries but each table will be in the same format and will all be in one final table. If I want the results for query 1 to be listed first and query2 second etc, what is the easiest way to do it?
Does UNION append the table or are is the combination random?
The SQL standard does not guarantee an order unless explicitly called for in an order by clause. In practice, this usually comes back chronologically, but I would not rely on it if the order is important.
Across a union you can control the order like this...
select
this,
that
from
(
select
this,
that
from
table1
union
select
this,
that
from
table2
)
order by
that,
this;
UNION appends the second query to the first query, so you have all the first rows first.
You can use:
SELECT Col1, Col2,...
FROM (
SELECT Col1, Col2,..., 1 AS intUnionOrder
FROM ...
) AS T1
UNION ALL (
SELECT Col1, Col2,..., 2 AS intUnionOrder
FROM ...
) AS T2
ORDER BY intUnionOrder, ...
How can I using group by with union in T-SQL? I want to group by the first column of a result of union, I wrote the following SQL but it doesn't work. I just don't know how to reference the specified column (in this case is 1) of the union result.
SELECT *
FROM ( SELECT a.id ,
a.time
FROM dbo.a
UNION
SELECT b.id ,
b.time
FROM dbo.b
)
GROUP BY 1
You need to alias the subquery. Thus, your statement should be:
Select Z.id
From (
Select id, time
From dbo.tablea
Union All
Select id, time
From dbo.tableb
) As Z
Group By Z.id
GROUP BY 1
I've never known GROUP BY to support using ordinals, only ORDER BY. Either way, only MySQL supports GROUP BY's not including all columns without aggregate functions performed on them. Ordinals aren't recommended practice either because if they're based on the order of the SELECT - if that changes, so does your ORDER BY (or GROUP BY if supported).
There's no need to run GROUP BY on the contents when you're using UNION - UNION ensures that duplicates are removed; UNION ALL is faster because it doesn't - and in that case you would need the GROUP BY...
Your query only needs to be:
SELECT a.id,
a.time
FROM dbo.TABLE_A a
UNION
SELECT b.id,
b.time
FROM dbo.TABLE_B b
Identifying the column is easy:
SELECT *
FROM ( SELECT id,
time
FROM dbo.a
UNION
SELECT id,
time
FROM dbo.b
)
GROUP BY id
But it doesn't solve the main problem of this query: what's to be done with the second column values upon grouping by the first? Since (peculiarly!) you're using UNION rather than UNION ALL, you won't have entirely duplicated rows between the two subtables in the union, but you may still very well have several values of time for one value of the id, and you give no hint of what you want to do - min, max, avg, sum, or what?! The SQL engine should give an error because of that (though some such as mysql just pick a random-ish value out of the several, I believe sql-server is better than that).
So, for example, change the first line to SELECT id, MAX(time) or the like!
with UnionTable as
(
SELECT a.id, a.time FROM dbo.a
UNION
SELECT b.id, b.time FROM dbo.b
) SELECT id FROM UnionTable GROUP BY id