I'm only about a day into using PostgreSQL and have what is pry a quite simple question. I want to create a left outer join to search for mismatch values. I'd like from the join create a subquery which selects the null values and then updates are based on this selection. What I have for the left outer join looks like this:
SELECT TableA.field1, TableA.field2, TableB.field3
FROM
TableA
LEFT OUTER JOIN TableB ON TableA.field1 = TableB.field1
This works for the join. However, I can't manage to figure out how to then use a subquery to return only rows where TableB.field1 is null.
You don't need a subquery:
SELECT TableA.field1, TableA.field2, TableB.field1
FROM TableA
LEFT OUTER JOIN TableB ON TableA.field1 = TableB.field1
where tableB.field1 IS NULL;
Not sure what you mean with "and then updates a based on this selection" though
Here is how you ...
Select rows which are not present in other table
I suppose you want to update rows based on this selection. Use the FROM clause to join more (derived) tables in an UPDATE:
UPDATE some_table t
SET (field1, field2, field3)
= (a.field1, a.field2, a.field3)
FROM (
SELECT a.a_id, a.field1, a.field2, a.field3
FROM tablea a
LEFT JOIN tableb b USING (field1)
WHERE b.field1 IS NULL
) a
WHERE t.a_id = a.a_id; -- join on the connecting column
Using the short syntax variant to update multiple columns.
Related
When I have have a statement like the one below, is there a way to select all values from tableA including those that don't connect to tableB (with b.value being NULL or empty)? Thanks for any help.
SELECT DISTINCT a.value, b.value
FROM tableA a
LEFT JOIN tableB b ON ....
The behavior you described is exactly what a left join would do. There's nothing extra you need to do (except for completing the join condition you left out, of course).
I have two tables:
I am looking for the results like mentioned in the last.
I tried union (only similar col can be merged), left join, right join i am getting repeated fields in Null areas what can be other options where i can get null without column repeating
A full join would get all results from both tables.
select
A.ID,
A.ColA,
A.ColB,
B.ColC,
B.ColD
from TableA A
full join Table B on A.ID = B.ID
Here is a good post to understand joins
You can try distinct:
select distinct * from
tableA a,
tableB b
where a.id = b.id;
It will not give any duplicate tuples.
I am trying to join 4 tables. Currently I've achieved it by doing this.
SELECT columns
FROM tableA
LEFT OUTER JOIN tableB ON tableB.address_id = tableA.address_id
INNER JOIN tableC ON tableC.company_id = tableA.company_id AND tableC.client_id = ?
UNION
SELECT columns
FROM tableA
LEFT OUTER JOIN tableB ON tableB.address_id = tableA.gaddress_id
INNER JOIN tableD ON tableD.company_id = tableA.company_id AND tableD.branch_id = ?
The structure of tableC and tableD is very similar. Let's say that tableC contains data for clients. And tableD contains data for client's branch. tableA are companies and tableB are addresses My goal is to get data from tableA that are joined to table B (All companies that has addresses) and all the data from tableD and also from tableC.
This wroks nice, but I am afraid that is would be very slow.
I think you can trick it like this:
First UNION between C,D and only the join to the rest of the query, it should improve the query significantly :
SELECT columns
FROM TableA
LEFT OUTER JOIN tableB ON tableB.address_id = tableA.address_id
INNER JOIN(SELECT Columns,'1' as ind_where FROM tableC
UNION ALL
SELECT Columns,'2' FROM TableD) joined_Table
ON (joined_Table.company_id = tableA.company_id AND joined_Table.New_Col_ID= ?)
The New_Col_ID -> just select both branch_id and client_id in the same column and alias it as New_Col_ID or what ever
In addition you can index the tables(if not exists yet) :
TableA(address_id,company_id)
TableB(address_id)
TableC(company_id,client_id)
TableD(company_id,branch_id)
Why should that be slow? You select client adresses and branch addresses and show the complete result. That seems straight-forward.
You join on IDs and this should be fast (as there should be indexes available accordingly). You may want to introduce composite indexes on
create index idx_c on tableC(client_id, company_id)
and
create index idx_d on tableD(branch_id, company_id)
However: UNION is a lot of work for the DBMS, because it has to look for and eliminate duplicates. Can there even be any? Otherwise use UNION ALL.
Try CTE so that you don't have to go through TableA and TableB twice for the union.
; WITH TempTable (Column1, Column2, ...)
AS ( SELECT columns
FROM tableA
LEFT OUTER JOIN tableB
ON tableB.address_id = tableA.gaddress_id
)
SELECT Columns
FROM TempTable
INNER JOIN tableC
ON tableC.company_id = tableA.company_id AND tableC.client_id = ?
UNION
SELECT Columns
FROM TempTable
INNER JOIN tableD ON tableD.company_id = tableA.company_id AND tableD.branch_id = ?
It is possible to delete records based on a satisfied condition with a join query?
For instance, I have a linking table joining 3 records. The query I have at the moment deletes records from this table where one of the id's isn't IN() an imploded Php array. I've come to realise that the query should only remove records from this table if the id's don't exist in the array and they belong to a certain other table based on the a link to another table.
For SQL Server, the command is slightly different:
DELETE FROM TableA
FROM TableA LEFT OUTER JOIN TableB ON TableA.Column = TableB.Column
WHERE TableB.Column IS NULL
No, that's not a typo, yes, you do need "FROM TableA" twice. At least, you need the second FROM (the first is optional). The following has the advantage that it works for both SQL Server and MySQL:
DELETE TableA
FROM TableA LEFT OUTER JOIN TableB ON TableA.Column = TableB.Column
WHERE TableB.Column IS NULL
I like to use EXISTS clauses for this:
DELETE FROM TableA
WHERE
<<put your array condition here>>
AND NOT EXISTS
(SELECT 1 FROM TableB Where TableB.ID=TableA.ID)
You can use :
DELETE Based on a Join:
DELETE A
FROM TableA AS A
LEFT OUTER JOIN TableB As B ON A.Id = B.TabaleAId
WHERE B.Column IS NULL
Delete With SubQuery:
DELETE
FROM TableA AS A
Where
A.id not in ( Select B.TabaleAId From Tab;eB As B )
or
DELETE FROM TableA
WHERE Not EXISTS
(
SELECT *
FROM TableB As B
Where B.TableAId = TableA.Id
)
DELETE Using Table Expressions:
With A
As
(
Select TableA.*
FROM TableA AS A
LEFT OUTER JOIN TableB As B ON A.Id = B.TabaleAId
WHERE B.Column IS NULL
)
Delete From A
DELETE FROM TableA
LEFT OUTER JOIN TableB
WHERE TableB.Column IS NULL
Will delete the records in tableA that don't have a corresponding record in TableB. Is that like what you are after?
DELETE FROM a
FROM TableA AS a LEFT OUTER JOIN TableB AS b
on a.CALENDAR_DATE = b.CALENDAR_DATE AND a.ID = b.ID
Where b.ID is null
You can first use the select statement and verify your records that you want to delete and then remove the select statement and add Delete FROM tablename with the above query syntax.
The easiest way to Delete based on join is as follow:
1.Write your query using SELECT statement instead of DELETE statement
SELECT COLUMNS
FROM Table1
INNER JOIN Table2 ON Table1.YYY = Table2.XXX
2.Replace SELECT COLUMNS with DELETE FROM TABLE
DELETE FROM Table1
FROM Table1
INNER JOIN Table2 ON Table1.YYY = Table2.XXX
Note that we need to specify FROM twice, one for DELETE part and one for JOIN part.
delete from TableA
where id in
(
select id from TableA
except select id from TableB
)
Which means "delete from tableA where id in table a but not in table b)
Otherwise a Merge statement might help you (when matched/not matched delete etc)
http://technet.microsoft.com/en-us/library/bb510625.aspx
Basically, what I want is if there is a record in tableB of type 'X' I want to see it, otherwise I don't, but I want all records from tableA.
I know I could accomplish this by putting the tableB.type = 'X' in the LEFT OUTER JOIN ON clause, but I can't do that because I'm limited to using only the where condition because I'm using a restricted query manager of a program I won't name, but I definitely hate. :)
SELECT *
FROM tableA
LEFT OUTER JOIN ON tableA.ID = tableB.ID
WHERE tableB.type = 'X'
How do I accomplish this?
EDIT
I've tried this, but I still don't get all records from tableA. I'm testing this on SQL server to avoid waiting for long periods for my query to run on the production system. I'm pretty sure the production system is using Oracle if that helps.
SELECT *
FROM tableA LEFT OUTER JOIN ON tableA.ID = tableB.ID
WHERE tableB.type = 'X' OR tableB.type IS NULL
Check for nulls in tableB:
SELECT *
FROM tableA LEFT OUTER JOIN ON tableA.ID = tableB.ID
WHERE tableB.type = 'X'
OR tableB.type IS NULL
That will get you everything from both tables when the join matches, and everything from tableA when there's no corresponding record in tableB.
If type can be null naturally, you'll want to change the condition to something more sound:
SELECT *
FROM tableA LEFT OUTER JOIN ON tableA.ID = tableB.ID
WHERE tableB.type = 'X'
OR tableB.ID IS NULL
Assuming ID is the primary key and cannot be null naturally, that will get the same result.
Don't know if you have access to the database, or if you have to query tableB specifically due to some other restriction, but you could always create a view of table b called tableBTypeX where the view is restricted to only those rows with type = x. Then you could left outer join against tableBTypeX . In your query, the join columns are ID columns, so they probably have indexes, making the query fine in terms of speed. In the case where the join columns are not indexed, joining against the view would be more efficient, because fewer rows are joined against, and joining against unindexed rows usually requires a full table scan, making it a much more time consuming query.
You can join against the "type X" records from tableB exclusively by amending the join condition:
SELECT
*
FROM
tableA
LEFT OUTER JOIN ON
tableA.ID = tableB.ID
AND tableB.type = 'X'
Is UNION possible?
SELECT *
FROM tableA
LEFT OUTER JOIN ON tableA.ID = tableB.ID
WHERE tableB.type = 'X'
UNION
SELECT *
FROM tableA
... or a CTE? Not sure how the name tableB would resolve though and can't test...
;WITH tableB AS
(
SELECT * FROM tableB WHERE type = 'X'
)
SELECT *
FROM
tableA
LEFT OUTER JOIN
tableB ON tableA.ID = tableB.ID