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
Related
I've got some SQL code working at the moment but I need to do another union. I want to ensure what I do is correct. Currently, this is what I have:
select * from (select * from stametadata
union select * from stajjmetadata)
I want to union on another table. Would this be correct?
select * from (select * from stametadata
union select * from stajjmetadata
union select * from staggmetadata)
Is this the neatest way to do it?
You can chain unions. To be honest, you don't even need the outer query:
SELECT * FROM stametadata
UNION
SELECT * FROM stajjmetadata
UNION
SELECT * FROM staggmetadata
I was recently asked this question and was a little stumped so I want to ask the experts...
Given two tables A & B, I want to return all the values from A and B that do not overlap. Think of two overlapping circles; how do we return all the data that is NOT in the overlapping center section? And, I had to use ANSI Standard SQL rather than Oracle syntax.
Assuming we want everything exclusive to both A & B, my answer was
select *
from A
cross join B
minus
(select a.common_column from a
intersect
select b.common_column)
Does this look correct, or even close? If it is correct, is there a more efficient way to do this?
BTW - my solution was soundly rejected....
Thank you!
Given the tables A and B, you are looking for (A U B) - (A & B). In other words, you need A union B minus their intersection. Remember A and B must be union-compatible for this query to work. I would do:
(select * from A
union
select * from B
)
minus
(select * from A
intersect
select * from B
)
May be full outer join?
select coalesce(A.col, B.col)
from A full outer join B on A.col = B.col
where A.col is null or B.col is null;
For computing a set symmetric difference, you can use a combination of MINUS and UNION ALL:
select * from (
(select * from A
minus
select * from B)
union all
(select * from B
minus
select * from A)
)
Your query was rejected because it is syntactically incorrect: the number of columns differ and it confuses cross join and union all. However, I think you have the right idea for solving this.
You can easily fix this:
(select *
from A
union all
select *
from B
) minus
(select *
from A
intersect
select *
from B
);
That is, combine everything using union all and then subtract the rows that occur in both tables.
Of course, if there is a single id, then you can use the id with join and other operations.
Just like Frank Schmitt answered in the meantime:
Here it is including a data example:
WITH
table_a(name) AS (
SELECT 'From_A_1'
UNION ALL SELECT 'From_A_2'
UNION ALL SELECT 'From_A_3'
UNION ALL SELECT 'From_A_4'
UNION ALL SELECT 'From_A_5'
UNION ALL SELECT 'From_BOTH_6'
UNION ALL SELECT 'From_BOTH_7'
UNION ALL SELECT 'From_BOTH_8'
)
,
table_b(name) AS (
SELECT 'From_B_1'
UNION ALL SELECT 'From_B_2'
UNION ALL SELECT 'From_B_3'
UNION ALL SELECT 'From_B_4'
UNION ALL SELECT 'From_B_5'
UNION ALL SELECT 'From_BOTH_6'
UNION ALL SELECT 'From_BOTH_7'
UNION ALL SELECT 'From_BOTH_8'
)
(SELECT * FROM table_a EXCEPT SELECT * FROM table_b)
UNION ALL
(SELECT * FROM table_b EXCEPT SELECT * FROM table_a)
ORDER BY name
;
name
From_A_1
From_A_2
From_A_3
From_A_4
From_A_5
From_B_1
From_B_2
From_B_3
From_B_4
From_B_5
You will need to select all the data from both tables, except where they overlap, and then combine the data with a union. The code provided should work for your example.
SELECT *
FROM
(
SELECT * FROM Table1
EXCEPT SELECT * FROM Table2
)
UNION
SELECT *
FROM
(
SELECT * FROM Table2
EXCEPT SELECT * FROM Table1
)
Hope this helps.
So this is fairly common knowledge to select rows from multiple tables and stack the results on top of each other:
SELECT * FROM table1
UNION
SELECT * FROM table2
UNION
...
However, if I want only a limited number of rows from each table, then how should I write it?
SELECT * FROM table1 LIMIT 2
UNION
SELECT * FROM table2 LIMIT 2
UNION
...
Clearly doesn't work.
Note that in my case, I have 51 tables, all with the same exact columns.
could be work this way
( SELECT * FROM table1 LIMIT 2 )
UNION
( SELECT * FROM table2 LIMIT 2 )
UNION
...
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!
I'm trying to get a UNION of 3 tables, each of which have 97 fields. I've tried the following:
select * from table1
union all
select * from table2
union all
select * from table3
This gives me an error message:
Too many fields defined.
I also tried explicitly selecting all the field names from the first table (ellipses added for brevity):
select [field1],[field2]...[field97] from table1
union all
select * from table2
union all
select * from table3
It works fine when I only UNION two tables like this:
select * from table1
union all
select * from table2
I shouldn't end up with more than 97 fields as a result of this query; the two-table UNION only has 97. So why am I getting Too many fields with 3 tables?
EDIT: As RichardTheKiwi notes below, Access is summing up the field count of each SELECT query in the UNION chain, which means that my 3 tables exceed the 255 field maximum. So instead, I need to write the query like this:
select * from table1
union all
select * from
(select * from table2
union all
select * from table3)
which works fine.
It appears that the number of fields being tracked (limit 255) is counted against ALL parts of the UNION ALL. So 3 x 97 = 291, which is in excess. You could probably create a query as a UNION all of 2 parts, then another query with that and the 3rd part.
I had two tables with 173 fields each (2 x 173 > 255!). So I had to resort to splitting the tables in half (keeping the primary key in both), before using the UNION statement and reassembling the resulting output tables using a JOIN.
select u1.*, u2.*
from (
select [field1_PKID],[field2],...,[field110]
from table1
union all
select [field1_PKID],[field2],...,[field110]
from table2
) as u1
inner join (
select [field1_PKID],[field111],...,[field173]
from table1
union all
select [field1_PKID],[field111],...,[field173]
from table2
) as u2
on [u1].[field1_PKID] = [u2].[field2_PKID]
Perhaps if your 3 tables have duplicate records you can go with UNION instead of UNION ALL which may reduce the number of fields to be tracked. Because UNION will always serve the business purpose which removes duplicates. In that case your query will be like following,
select * from table1
union
select * from table2
union
select * from table3;