I would like to create 2 columns of data out of a single union query of 2 tables with same field. I have 2 tables with "Utilizations" field in each table.
I tried the following query but I got an error.
select Utilizations as "Utilizations A", Utilizations as "Utilizations B" from
(select Utilizations as A, 0 as B from TableA
union all
select 0 as A, Utilizations as B from TableB)
First off, you need to alias your subquery, and second of all, you needed to refer to your columns in your outer query as A and B, not utilitizations:
select A as "Utilizations A",
B as "Utilizations B"
from
(select Utilizations as A,
0 as B
from TableA
union all
select 0 as A,
Utilizations as B
from TableB
)AS t
Related
Hay All,
is it possible to run more than 1 select statement after using with?
first select statement works fine, as soon as i add another select statement i got a error.
with
a as (select a,b,c from Table1 with(readuncommitted)),
b as (select d,e,f from Table2 with(readuncommitted))
select * from a
select * from b
expected output:
Table 1
a
Table 2
b
Well the way CTEs will behave is that they will only be in scope for the first query, but not the second. You could perhaps do a union query here:
SELECT a, b, c, 'Table1' AS src FROM a
UNION ALL
SELECT d, e, f, 'Table2' FROM b;
Or, you could move the b CTE to before the second query:
WITH a AS (
SELECT a, b, c
FROM Table1
WITH(readuncommitted)
)
SELECT * FROM a;
WITH b AS (
SELECT d, e, f
FROM Table2
WITH(readuncommitted)
)
SELECT * FROM b;
hay DasD,
You can not use multiple select for cte, but you can use more than one CTE like this.
with
a as (select a,b,c from Table1 with(readuncommitted)),
b as (select d,e,f from Table2 with(readuncommitted))
select * from a,b
You have to explain to the database, what you wantfrom bith tables.
as both have the same structure you can use UNION to join them vertically
with
a as (select a,b,c from Table1 with(readuncommitted)),
b as (select d,e,f from Table2 with(readuncommitted))
select * from a
UNION
select * from b
From the docs:
"A CTE must be followed by a single SELECT, INSERT, UPDATE, or DELETE statement that references some or all the CTE columns."
Source
I have 3 tables. All of them have a column - id. I want to find if there is any value that is common across the tables. Assuming that the tables are named a.b and c, if id value 3 is present is a and b, there is a problem. The query can/should exit at the first such occurrence. There is no need to probe further. What I have now is something like
( select id from a intersect select id from b )
union
( select id from b intersect select id from c )
union
( select id from a intersect select id from c )
Obviously, this is not very efficient. Database is PostgreSQL, version 9.0
id is not unique in the individual tables. It is OK to have duplicates in the same table. But if a value is present in just 2 of the 3 tables, that also needs to be flagged and there is no need to check for existence in he third table, or check if there are more such values. One value, present in more than one table, and I can stop.
Although id is not unique within any given table, it should be unique across the tables; a union of distinct id should be unique, so:
select id from (
select distinct id from a
union all
select distinct id from b
union all
select distinct id from c) x
group by id
having count(*) > 1
Note the use of union all, which preserves duplicates (plain union removes duplicates).
I would suggest a simple join:
select a.id
from a join
b
on a.id = b.id join
c
on a.id = c.id
limit 1;
If you have a query that uses union or group by (or order by, but that is not relevant here), then you need to process all the data before returning a single row. A join can start returning rows as soon as the first values are found.
An alternative, but similar method is:
select a.id
from a
where exists (select 1 from b where a.id = b.id) and
exists (select 1 from c where a.id = c.id);
If a is the smallest table and id is indexes in b and c, then this could be quite fast.
Try this
select id from
(
select distinct id, 1 as t from a
union all
select distinct id, 2 as t from b
union all
select distinct id, 3 as t from c
) as t
group by id having count(t)=3
It is OK to have duplicates in the same table.
The query can/should exit at the first such occurrence.
SELECT 'OMG!' AS danger_bill_robinson
WHERE EXISTS (SELECT 1
FROM a,b,c -- maybe there is a place for old-style joins ...
WHERE a.id = b.id
OR a.id = c.id
OR c.id = b.id
);
Update: it appears the optimiser does not like carthesian joins with 3 OR conditions. The below query is a bit faster:
SELECT 'WTF!' AS danger_bill_robinson
WHERE exists (select 1 from a JOIN b USING (id))
OR exists (select 1 from a JOIN c USING (id))
OR exists (select 1 from c JOIN b USING (id))
;
I have four tables Table A, Table B, Table C and Table D. The schema of all four tables are identical. I need to union these four tables in the following way:
If a record is present in Table A then that is considered in the output table.
If a record is present in Table B then it is considered in the output table ONLY if it is not present in Table A.
If a record is present in Table C then it is considered ONLY if it is not present in Table A and Table B.
If a record is present in Table D then it is considered ONLY if it is not present in Table A, Table B, and Table C.
Note -
Every table has a column which identifies the table itself for every record (I don't know if this is of any importance)
Records are identified based on a particular column - Column X which is not unique even within each table
You could do something like (only two cases shown but you should see how to extend this)
WITH CTE1 AS
(
SELECT 't1' as Source, X, Y
FROM t1
UNION ALL
SELECT 't2' as Source, X, Y
FROM t2
), CTE2 AS
(
SELECT *,
RANK() OVER (PARTITION BY X
ORDER BY CASE Source
WHEN 't1' THEN 1
WHEN 't2' THEN 2
END) As RN
FROM CTE1
)
SELECT X,Y
FROM CTE2
WHERE RN=1
I would be inclined to do this using not exists:
select a.*
from a
union all
select b.*
from b
where not exists (select 1 from a where a.x = b.x)
union all
select c.*
from c
where not exists (select 1 from a where a.x = c.x) and
not exists (select 1 from b where b.x = c.x)
union all
select d.*
from d
where not exists (select 1 from a where a.x = d.x) and
not exists (select 1 from b where b.x = d.x) and
not exists (select 1 from c where c.x = d.x);
If you have an index on the x column in each table, then this should be the fastest method.
This will work as long as there are no NULL columns, or if columns for a record that exists in table with higher precedence are NULL you can assume the same column will NULL in tables with lower precedence.
SELECT coalesce(a.column1, b.column1, c.column1, d.column1) column1
,coalesce(a.column2, b.column2, c.column2, d.column2) column2
,coalesce(a.column3, b.column3, c.column3, d.column3) column3
--...
,coalesce(a.columnN, b.columnN, c.columnN, d.columnN) columnN
FROM TableA a
FULL JOIN TableB b on b.ColumnX = a.ColumnX
FULL JOIN TableC c on c.ColumnX = a.ColumnX or c.ColumnX = b.ColumnX
FULL JOIN TableD d on d.ColumnX = a.ColumnX or d.ColumnX = b.ColumnX or d.ColumnX = c.ColumnX
If the NULL values matter, you can switch to a more-complicated (and likely slower) CASE version:
CASE WHEN a.columnX IS NOT NULL THEN a.column1
WHEN b.columnX IS NOT NULL THEN b.column1
WHEN c.columnX IS NOT NULL THEN c.column1
WHEN d.columnX IS NOT NULL THEN d.column1 END column1
Of course, you can mix and match, so columns that are not nullable can use the former syntax, and columns where NULL values matter use the latter.
Hopefully the purpose of this is to fix the broken schema and put this data all in the same table, where it belongs.
This might seem stupid, but if, by any chance, you can leave out the table-identifying column and you also want to eliminate duplicate records (from within one table) too then the most straightforward answer would be
select <all columns without table identifier> from tableA
union
select <all columns without table identifier> from tableB
union
select <all columns without table identifier> from tableC
...
This is exactly, what union was designed to do: add rows only if they do not already exist before.
I made several attempts at googling a solution to this but I'm finding a hard time generating keywords for an accurate search.
Say I have a table with the following information.
A, B
1, 1
1, 2
2, 1
If I perform a group by operation on both columns A, B, I'll get a table indexed by the same set, but I'm interested in something of the form:
A, B, nRecords
1, 1, 1
1, 2, 1
2, 1, 1
2, 2, 0
Query:
SELECT
A, B, COUNT(*) nRecords
FROM
table
GROUP BY
A, B
will not include information for the A = 2, B = 2 case. Any thoughts on moving forward? This needs to be abstracted to large distinct values in both columns.
select a.A, a.B, count(*)
from
(select distinct A from T) as a
cross join
(select distinct B from T) as b
left outer join T as t on t.A = a.A and t.B = b.B
group by a.A, a.B
I have to tables, say A and B and a common column X which isn't nullable.
Query 1:
SELECT COUNT(*)
FROM A
WHERE A.X in
(SELECT distinct(B.X) FROM B)
Query 2:
SELECT COUNT(*)
FROM B
WHERE B.X in
(SELECT distinct(X) FROM A)
Query 3:
SELECT COUNT(*)
FROM A, B
WHERE A.X=B.X
Query 1 results 5990. Query 2 and 3 results 6222. Removing distinct or checking distinct count on top doesn't change the results. Can someone explain why the results aren't the same for all queries as they all return intersection count?
Assume A has values
A
B
C
Assume B has values
A
B
C
D
E
C
in this case A would have a count of 3 (QRY1)
while B would have a count of 4 since c is repeated (QRY2)
when you use a join C will match will all values of C has more duplicates than A. A may have duplicates but fewer of them. 4 again (QRY3)