Selecting the union:
select * from table1
union
select * from table1_backup
What is the query to select the intersection?
In SQL Server intersect
select * from table1
intersect
select * from table1_backup
SELECT *
FROM table1
WHERE EXISTS
(SELECT *
FROM table1_backup
WHERE table1.pk = table1_backup.pk)
works
For questions like this, I tend to go back to this visual resource:
A Visual Explanation of SQL Joins
inner join i think:
suppose T1 and T2 have the same structure:
select T1.* from
T1 inner join T2 on T1.pkField = T2.pkField
"intersect" is also part of standard SQL.
Inner join gives a different answer.
here is a solution for mySQL:
CREATE TABLE table1(
id INT(10),
fk_id INT(10),
PRIMARY KEY (id, fk_id),
FOREIGN KEY table1(id) REFERENCES another_table(id),
FOREIGN KEY table1(fk_id) REFERENCES other_table(id)
);
SELECT table1.* FROM table1 as t0
INNER JOIN table1 as a ON (t0.id = a.id and fk_id=1)
INNER JOIN table1 as b ON (t0.id = b.id and fk_id=2)
INNER JOIN table1 as c ON (t0.id = c.id and fk_id=3)
ORDER BY table1.id;
Basically you have an table of mathematical subsets (ie. 1={1, 2 ,3}, 2={3, 4, 2}, ... , n={1, 4, 7}) with an attribute id, which is the set number, and fk_ id, which references a PRIMARY KEY of a table of elements, the superset (meaning possible values for the numbers in the curly braces). For those not mathematically inclined, let's pretend you have a table, 'other_ table', which is a list of items, and another table, 'another_ table', which is a list of transaction numbers, and both tables form a many-to-many relationship, thus producing 'table1'. now let's pretend you wanted to know the id's in 'another_ table' which had items 1, 2, and 3. that's the query to do it.
An intersect on two identical tables a and b can be done in this manner:
SELECT a.id, a.name
FROM a INNER JOIN b
USING (id, name)
subqueries?! really?
to get the intersection of table1 and table2:
SELECT * FROM table1, table2 WHERE table1.pk=table2.pk;
select distinct * from (select * from table1 union select * from table1_backup)
Related
Table 1
Table 2
Here wish to get the data from Table 1 which is created between 5\09\2018 to 26\12\2018.
Here PostID is the foreign key.
Thanks in advance
You can join both tables and use where statement to retrieve the relevant data,
Select *
from table1 t1
inner join table2 t2
on t1.PostID=t2.PostID
where t1.datecreated between '2018-09-05' and '2018-12-26'
Select *
from table1 t1
inner join table2 t2
on t1.PostID=t2.PostID
where t2.PostID=1
For inner join foreign key is mandatory, and the reference column will come in the join condition.
If you just query data from Table 1, you may write the query like this.
select
*
from table1 T
where T.DateCreated between '2018-09-05 00:00:00' and '2018-12-26 23:59:59'
and exists (select 1 from table2 where PostID=T.PostID)
Best Regards,
Will
I am currently using Microsoft Access 2013, and I am trying to join Table1 and Table2 together, but the problem is that Table2 is massive. Table1 is a list of part, vendor combinations with PK as part, vendor. Table2 is a table I created with the top2 most recent quotes for each part,vendor combination. All these quotes were pulled from a table with PK quote_id. I think my creation of Table2 might be the problem, because I cannot create Table2 with every part,vendor combination (i have to filter out by vendor). This is the query I used for Table2.
a.part, a.vendor, a.quote_date
FROM quoteTable AS a
WHERE a.quote_date > DATEADD("yyyy", -3, DATE()) AND
a.quote_date IN
(SELECT TOP 2 quote_date
FROM quoteTable
WHERE quote_date > DATEADD("yyyy", -3, DATE()) AND
part=a.part AND vendor=a.vendor
ORDER BY quote_date DESC)
If anyone knows a better way to select the top 2 most recent quotes from the table for each part,vendor combination, I would really appreciate it. As for the join, this works but would take too long.
SELECT *
FROM Table1 AS a INNER JOIN Table2 AS b ON a.id = b.id
I am wondering if there was a way I could use the id from Table1 to filter Table2? Something like this:
SELECT *
FROM Table1 AS a INNER JOIN
(SELECT * FROM Table2 WHERE id=a.id) AS b ON a.id = b.id
You definitely could use:
SELECT *
FROM Table1 AS a
INNER JOIN
(SELECT * FROM Table2 WHERE id=a.id) AS b
ON a.id = b.id
Or you could use :
With CTE
as
(
SELECT *
FROM Table2
WHERE id in (select id from table1)
)
SELECT *
FROM Table1 AS a
INNER JOIN
CTE
ON CTE.Id = a.Id
For performance issue, you could try to create index on id column from both tables, or try to limit the selected column from your result.
The real solution is that you need an index on TABLE2.id. I am assuming that it is not the primary key of that table, because it probably is the primary key of TABLE1, and why would you have two tables with the exact same, matching primary keys? It would not be a normalized layout. But then again, there are times when it makes sense to de-normalize.
I have two tables with binding primary key in database and I desire to find a disjoint set between them. For example,
Table1 has columns (ID, Name) and sample data: (1 ,John), (2, Peter), (3, Mary)
Table2 has columns (ID, Address) and sample data: (1, address2), (2, address2)
So how do I create a SQL query so I can fetch the row with ID from table1 that is not in table2. In this case, (3, Mary) should be returned?
PS: The ID is the primary key for those two tables.
Try this
SELECT ID, Name
FROM Table1
WHERE ID NOT IN (SELECT ID FROM Table2)
Use LEFT JOIN
SELECT a.*
FROM table1 a
LEFT JOIN table2 b
on a.ID = b.ID
WHERE b.id IS NULL
There are basically 3 approaches to that: not exists, not in and left join / is null.
LEFT JOIN with IS NULL
SELECT l.*
FROM t_left l
LEFT JOIN
t_right r
ON r.value = l.value
WHERE r.value IS NULL
NOT IN
SELECT l.*
FROM t_left l
WHERE l.value NOT IN
(
SELECT value
FROM t_right r
)
NOT EXISTS
SELECT l.*
FROM t_left l
WHERE NOT EXISTS
(
SELECT NULL
FROM t_right r
WHERE r.value = l.value
)
Which one is better? The answer to this question might be better to be broken down to major specific RDBMS vendors. Generally speaking, one should avoid using select ... where ... in (select...) when the magnitude of number of records in the sub-query is unknown. Some vendors might limit the size. Oracle, for example, has a limit of 1,000. Best thing to do is to try all three and show the execution plan.
Specifically form PostgreSQL, execution plan of NOT EXISTS and LEFT JOIN / IS NULL are the same. I personally prefer the NOT EXISTS option because it shows better the intent. After all the semantic is that you want to find records in A that its pk do not exist in B.
Old but still gold, specific to PostgreSQL though: https://explainextended.com/2009/09/16/not-in-vs-not-exists-vs-left-join-is-null-postgresql/
Fast Alternative
I ran some tests (on postgres 9.5) using two tables with ~2M rows each. This query below performed at least 5* better than the other queries proposed:
-- Count
SELECT count(*) FROM (
(SELECT id FROM table1) EXCEPT (SELECT id FROM table2)
) t1_not_in_t2;
-- Get full row
SELECT table1.* FROM (
(SELECT id FROM table1) EXCEPT (SELECT id FROM table2)
) t1_not_in_t2 JOIN table1 ON t1_not_in_t2.id=table1.id;
Keeping in mind the points made in #John Woo's comment/link above, this is how I typically would handle it:
SELECT t1.ID, t1.Name
FROM Table1 t1
WHERE NOT EXISTS (
SELECT TOP 1 NULL
FROM Table2 t2
WHERE t1.ID = t2.ID
)
SELECT COUNT(ID) FROM tblA a
WHERE a.ID NOT IN (SELECT b.ID FROM tblB b) --For count
SELECT ID FROM tblA a
WHERE a.ID NOT IN (SELECT b.ID FROM tblB b) --For results
I've got a scenario where I need to do a join across three tables.
table #1 is a list of users
table #2 contains users who have trait A
table #3 contains users who have trait B
If I want to find all the users who have trait A or trait B (in one simple sql) I think I'm stuck.
If I do a regular join, the people who don't have trait A won't show up in the result set to see if they have trait B (and vice versa).
But if I do an outer join from table 1 to tables 2 and 3, I get all the rows in table 1 regardless of the rest of my where clause specifying a requirement against tables 2 or 3.
Before you come up with multiple sqls and temp tables and whatnot, this program is far more complex, this is just the simple case. It dynamically creates the sql based on lots of external factors, so I'm trying to make it work in one sql.
I expect there are combinations of in or exists that will work, but I was hoping for some thing simple.
But basically the outer join will always yield all results from table 1, yes?
SELECT *
FROM table1
LEFT OUTER
JOIN table2
ON ...
LEFT OUTER
JOIN table3
ON ...
WHERE NOT (table2.pk IS NULL AND table3.pk IS NULL)
or if you want to be sneaky:
WHERE COALESCE(table2.pk, table3.pk) IS NOT NULL
but for you case, i simply suggest:
SELECT *
FROM table1
WHERE table1.pk IN (SELECT fk FROM table2)
OR table1.pk IN (SELECT fk FROM table3)
or the possibly more efficient:
SELECT *
FROM table1
WHERE table1.pk IN (SELECT fk FROM table2 UNION (SELECT fk FROM table3)
If you really just want the list of users that have one trait or the other, then:
SELECT userid FROM users
WHERE userid IN (SELECT userid FROM trait_a UNION SELECT userid FROM trait_b)
Regarding outerjoin specifically, longneck's answer looks like what I was in the midst of writing.
I think you could do a UNION here.
May I suggest:
SELECT columnList FROM Table1 WHERE UserID IN (SELECT UserID FROM Table2)
UNION
SELECT columnList FROM Table1 WHERE UserID IN (SELECT UserID FROM Table3)
Would something like this work? Keep in mind depending on the size of the tables left outer joins can be very expensive with regards to performance.
Select *
from table1
where userid in (Select t.userid
From table1 t
left outer join table2 t2 on t1.userid=t2.userid and t2.AttributeA is not null
left outer join table3 t3 on t1.userid=t3.userid and t3.AttributeB is not null
group by t.userid)
If all you want is the ids of the users then
SELECT UserId From Table2
UNION
SELECT UserId From Table3
is totally sufficient.
If you want some more infos from Table1 on these users, you can join the upper SQL to Table 1:
SELECT <list of columns from Table1>
FROM Table1 Join (
SELECT UserId From Table2
UNION
SELECT UserId From Table3) User on Table1.UserID = Users.UserID
Here is my situation:
Table one contains a set of data that uses an id for an unique identifier. This table has a one to many relationship with about 6 other tables such that.
Given Table 1 with Id of 001:
Table 2 might have 3 rows with foreign key: 001
Table 3 might have 12 rows with foreign key: 001
Table 4 might have 0 rows with foreign key: 001
Table 5 might have 28 rows with foreign key: 001
I need to write a report that lists all of the rows from Table 1 for a specified time frame followed by all of the data contained in the handful of tables that reference it.
My current approach in pseudo code would look like this:
select * from table 1
foreach(result) {
print result;
select * from table 2 where id = result.id;
foreach(result2) {
print result2;
}
select * from table 3 where id = result.id
foreach(result3) {
print result3;
}
//continued for each table
}
This means that the single report can run in the neighbor hood of 1000 queries. I know this is excessive however my sql-fu is a little weak and I could use some help.
LEFT OUTER JOIN Tables2-N on Table1
SELECT Table1.*, Table2.*, Table3.*, Table4.*, Table5.*
FROM Table1
LEFT OUTER JOIN Table2 ON Table1.ID = Table2.ID
LEFT OUTER JOIN Table3 ON Table1.ID = Table3.ID
LEFT OUTER JOIN Table4 ON Table1.ID = Table4.ID
LEFT OUTER JOIN Table5 ON Table1.ID = Table5.ID
WHERE (CRITERIA)
Join doesn't do it for me. I hate having to de-tangle the data on the client side. All those nulls from left-joining.
Here's a set-based solution that doesn't use Joins.
INSERT INTO #LocalCollection (theKey)
SELECT id
FROM Table1
WHERE ...
SELECT * FROM Table1 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table2 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table3 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table4 WHERE id in (SELECT theKey FROM #LocalCollection)
SELECT * FROM Table5 WHERE id in (SELECT theKey FROM #LocalCollection)
Ah! Procedural! My SQL would look like this, if you needed to order the results from the other tables after the results from the first table.
Insert Into #rows Select id from Table1 where date between '12/30' and '12/31'
Select * from Table1 t join #rows r on t.id = r.id
Select * from Table2 t join #rows r on t.id = r.id
--etc
If you wanted to group the results by the initial ID, use a Left Outer Join, as mentioned previously.
You may be best off to use a reporting tool like Crystal or Jasper, or even XSL-FO if you are feeling bold. They have things built in to handle specifically this. This is not something the would work well in raw SQL.
If the format of all of the rows (the headers as well as all of the details) is the same, it would also be pretty easy to do it as a stored procedure.
What I would do: Do it as a join, so you will have the header data on every row, then use a reporting tool to do the grouping.
SELECT * FROM table1 t1
INNER JOIN table2 t2 ON t1.id = t2.resultid -- this could be a left join if the table is not guaranteed to have entries for t1.id
INNER JOIN table2 t3 ON t1.id = t3.resultid -- etc
OR if the data is all in the same format you could do.
SELECT cola,colb FROM table1 WHERE id = #id
UNION ALL
SELECT cola,colb FROM table2 WHERE resultid = #id
UNION ALL
SELECT cola,colb FROM table3 WHERE resultid = #id
It really depends on the format you require the data in for output to the report.
If you can give a sample of how you would like the output I could probably help more.
Join all of the tables together.
select * from table_1 left join table_2 using(id) left join table_3 using(id);
Then, you'll want to roll up the columns in code to format your report as you see fit.
What I would do is open up cursors on the following queries:
SELECT * from table1 order by id
SELECT * from table1 r, table2 t where t.table1_id = r.id order by r.id
SELECT * from table1 r, table3 t where t.table1_id = r.id order by r.id
And then I would walk those cursors in parallel, printing your results. You can do this because all appear in the same order. (Note that I would suggest that while the primary ID for table1 might be named id, it won't have that name in the other tables.)
Do all the tables have the same format? If not, then if you have to have a report that can display the n different types of rows. If you are only interested in the same columns then it is easier.
Most databases have some form of dynamic SQL. In that case you can do the following:
create temporary table from
select * from table1 where rows within time frame
x integer
sql varchar(something)
x = 1
while x <= numresults {
sql = 'SELECT * from table' + CAST(X as varchar) + ' where id in (select id from temporary table'
execute sql
x = x + 1
}
But I mean basically here you are running one query on your main table to get the rows that you need, then running one query for each sub table to get rows that match your main table.
If the report requires the same 2 or 3 columns for each table you could change the select * from tablex to be an insert into and get a single result set at the end...