Mysql question.
I want to export one single row from one table with a catch: I want to pull together with it all the rows in all other tables referenced from the initial row by foreign keys - and referenced from the new rows too, recursively, until I get all rows that the initial one "needs to exist".
How can I do that?
Add more inner joins until you make it through your data structure
Select * from table1 t1
inner join table2 t2 on
t1.pk = t2.fk
inner join table3 t3 on
t2.pk = t3.fk
.......
where t1.pk = {pk id number} limit 0,1
Related
I need to join two tables together based on a three-column key stack. The problem is sometimes one of the key columns is translated and mapped differently in another table. I will attempt to example my issue using code:
select t1.TQ
from table1 t1
left join table2 t2 on t1.comp_cd = t2.comp_cd and t1.plcy_frm = t2.plcy_frm
and t1.val_cd = t2.val_cd
The columns "comp_cd" and "plcy_frm" are fine, however the problem is with val_cd. Sometimes the val_cd in table2 does not map correctly to table1 and must go through a third table, table3. Table3 structure is below:
Val_Cd Mapped_Val_Cd
A123 A564
So -> I need to join on Mapped_Val_Cd value when it exists in Table3, but join on Val_Cd from Table2 when Val_Cd does not exist in Table3.
I hope this makes sense - I have tried Case when exists syntax but cannot get that to work.
Assuming there are no duplicates in table3, you can left join it in and then choose the value that you want in the on clause:
select t1.TQ
from table1 t1 left join
table3 t3
on t1.val_cd = t3.val_cd
table2 t2
on t1.comp_cd = t2.comp_cd and
t1.plcy_frm = t2.plcy_frm and
t1.val_cd = coalesce(t3.Mapped_Val_Cd, t2.val_cd);
I have two tables with 3.5 million rows of data. I am creating a left join between the two to create a new view.
Code 1:
SELECT t1.c1,t1.c2,t2.c3,t2.c4
from table1 as t1
left join table2 as t2
on t1.Location=t2.Location and t1.OrderNumber=t2.OrderNumber and t1.Customer=t2.Customer
Code 2:
SELECT t1.c1,t1.c2,t2.c3,t2.c4
from table1 as t1
left join table2 as t2
on t1.OrderNumber=t2.OrderNumber
Both snippets of code give the same desired result as the Order number field in table 2 has only unique values.
Is it better to give more fields to JOIN compared to only one?
SELECT t1.c1,t1.c2,t2.c3,t2.c4
from table1 as t1
left join table2 as t2
on t1.Location = t2.Location
and t1.OrderNumber = t2.OrderNumber
and t1.Customer = t2.Customer
If OrderNumber is the PK of either table then adding additional fields will not change the results and it will not improve performance unless an index as not present on the other side.
If Order number field in table 2 has only unique values it would not change the query. If it is a PK or has a unique constraint/index then addition fields would not help unless what Table2.OrderNumber was joined to was not indexed.
I would like to delete records from a table if the corresponding record is not present in another table.
I.e. table1 has one-to-many relationship with table2. I need to delete orphaned records from table2 where table2.id is not present in table1.
I have tried this in Access:
DELETE *
FROM t2
RIGHT JOIN t2
ON t1.id = t2.id
WHERE t1.id is NULL
but I get "Syntax error in JOIN operation". I cannot see what is wrong.
Remove the * after DELETE..
I would have solved it like this:
DELETE FROM t2
WHERE id not in (
SELECT id from t1);
Not sure if deleting with a join will work. It would need to be a LEFT JOINthough, as you want to delete all the rows in the first part of the join that is not joined with anything. Also, you are joining t2 with itself, guessing it's just a typo..
This will help:
DELETE
from t2
FROM t1
RIGHT JOIN t2
ON t1.id = t2.id
WHERE t2.id is NULL
I had the same need as #Elizabeth and I found that #Tobb's method worked...but was slow as molasses, taking about a minute to execute on my table. I found that the following sequence of SQL commands accomplishes the same result in under one second:
ALTER TABLE t2 ADD COLUMN [USED] YESNO;
UPDATE t2 SET [USED]=true WHERE id IN (SELECT id FROM t1);
DELETE FROM t2 WHERE [USED] <> true;
ALTER TABLE t2 DROP COLUMN [USED];
There is no * in DELETE statement, so change it like this:
DELETE
FROM t2
WHERE id not in (SELECT id FROM t1)
I can't seem to ever remember this query!
I want to delete all rows in table1 whose ID's are the same as in Table2.
So:
DELETE table1 t1
WHERE t1.ID = t2.ID
I know I can do a WHERE ID IN (SELECT ID FROM table2) but I want to do this query using a JOIN if possible.
DELETE t1
FROM Table1 t1
JOIN Table2 t2 ON t1.ID = t2.ID;
I always use the alias in the delete statement as it prevents the accidental
DELETE Table1
caused when failing to highlight the whole query before running it.
DELETE Table1
FROM Table1
INNER JOIN Table2 ON Table1.ID = Table2.ID
There is no solution in ANSI SQL to use joins in deletes, AFAIK.
DELETE FROM Table1
WHERE Table1.id IN (SELECT Table2.id FROM Table2)
Later edit
Other solution (sometimes performing faster):
DELETE FROM Table1
WHERE EXISTS( SELECT 1 FROM Table2 Where Table1.id = Table2.id)
PostgreSQL implementation would be:
DELETE FROM t1
USING t2
WHERE t1.id = t2.id;
Try this:
DELETE Table1
FROM Table1 t1, Table2 t2
WHERE t1.ID = t2.ID;
or
DELETE Table1
FROM Table1 t1 INNER JOIN Table2 t2 ON t1.ID = t2.ID;
I think that you might get a little more performance if you tried this
DELETE FROM Table1
WHERE EXISTS (
SELECT 1
FROM Table2
WHERE Table1.ID = Table2.ID
)
This will delete all rows in Table1 that match the criteria:
DELETE Table1
FROM Table2
WHERE Table1.JoinColumn = Table2.JoinColumn And Table1.SomeStuff = 'SomeStuff'
Found this link useful
Copied from there
Oftentimes, one wants to delete some records from a table based on criteria in another table. How do you delete from one of those tables without removing the records in both table?
DELETE DeletingFromTable
FROM DeletingFromTable INNER JOIN CriteriaTable
ON DeletingFromTable.field_id = CriteriaTable.id
WHERE CriteriaTable.criteria = "value";
The key is that you specify the name of the table to be deleted from as the SELECT. So, the JOIN and WHERE do the selection and limiting, while the DELETE does the deleting. You're not limited to just one table, though. If you have a many-to-many relationship (for instance, Magazines and Subscribers, joined by a Subscription) and you're removing a Subscriber, you need to remove any potential records from the join model as well.
DELETE subscribers, subscriptions
FROM subscribers INNER JOIN subscriptions
ON subscribers.id = subscriptions.subscriber_id
INNER JOIN magazines
ON subscriptions.magazine_id = magazines.id
WHERE subscribers.name='Wes';
Deleting records with a join could also be done with a LEFT JOIN and a WHERE to see if the joined table was NULL, so that you could remove records in one table that didn't have a match (like in preparation for adding a relationship.) Example post to come.
Since the OP does not ask for a specific DB, better use a standard compliant statement.
Only MERGE is in SQL standard for deleting (or updating) rows while joining something on target table.
merge table1 t1
using (
select t2.ID
from table2 t2
) as d
on t1.ID = d.ID
when matched then delete;
MERGE has a stricter semantic, protecting from some error cases which may go unnoticed with DELETE ... FROM. It enforces 'uniqueness' of match : if many rows in the source (the statement inside using) match the same row in the target, the merge must be canceled and an error must be raised by the SQL engine.
To Delete table records based on another table
Delete From Table1 a,Table2 b where a.id=b.id
Or
DELETE FROM Table1
WHERE Table1.id IN (SELECT Table2.id FROM Table2)
Or
DELETE Table1
FROM Table1 t1 INNER JOIN Table2 t2 ON t1.ID = t2.ID;
I often do things like the following made-up example. (This example is from Informix SE running on Linux.)
The point of of this example is to delete all real estate exemption/abatement transaction records -- because the abatement application has a bug -- based on information in the real_estate table.
In this case last_update != nullmeans the account is not closed, and res_exempt != 'p' means the accounts are not personal property (commercial equipment/furnishings).
delete from trans
where yr = '16'
and tran_date = '01/22/2016'
and acct_type = 'r'
and tran_type = 'a'
and bill_no in
(select acct_no from real_estate where last_update is not null
and res_exempt != 'p');
I like this method, because the filtering criteria -- at least for me -- is easier to read while creating the query, and to understand many months from now when I'm looking at it and wondering what I was thinking.
Referencing MSDN T-SQL DELETE (Example D):
DELETE FROM Table1
FROM Tabel1 t1
INNER JOIN Table2 t2 on t1.ID = t2.ID
This is old I know, but just a pointer to anyone using this ass a reference. I have just tried this and if you are using Oracle, JOIN does not work in DELETE statements.
You get a the following message:
ORA-00933: SQL command not properly ended.
While the OP doesn't want to use an 'in' statement, in reply to Ankur Gupta, this was the easiest way I found to delete the records in one table which didn't exist in another table, in a one to many relationship:
DELETE
FROM Table1 as t1
WHERE ID_Number NOT IN
(SELECT ID_Number FROM Table2 as t2)
Worked like a charm in Access 2016, for me.
delete
table1
from
t2
where
table1.ID=t2.ID
Works on mssql
I can't seem to ever remember this query!
I want to delete all rows in table1 whose ID's are the same as in Table2.
So:
DELETE table1 t1
WHERE t1.ID = t2.ID
I know I can do a WHERE ID IN (SELECT ID FROM table2) but I want to do this query using a JOIN if possible.
DELETE t1
FROM Table1 t1
JOIN Table2 t2 ON t1.ID = t2.ID;
I always use the alias in the delete statement as it prevents the accidental
DELETE Table1
caused when failing to highlight the whole query before running it.
DELETE Table1
FROM Table1
INNER JOIN Table2 ON Table1.ID = Table2.ID
There is no solution in ANSI SQL to use joins in deletes, AFAIK.
DELETE FROM Table1
WHERE Table1.id IN (SELECT Table2.id FROM Table2)
Later edit
Other solution (sometimes performing faster):
DELETE FROM Table1
WHERE EXISTS( SELECT 1 FROM Table2 Where Table1.id = Table2.id)
PostgreSQL implementation would be:
DELETE FROM t1
USING t2
WHERE t1.id = t2.id;
Try this:
DELETE Table1
FROM Table1 t1, Table2 t2
WHERE t1.ID = t2.ID;
or
DELETE Table1
FROM Table1 t1 INNER JOIN Table2 t2 ON t1.ID = t2.ID;
I think that you might get a little more performance if you tried this
DELETE FROM Table1
WHERE EXISTS (
SELECT 1
FROM Table2
WHERE Table1.ID = Table2.ID
)
This will delete all rows in Table1 that match the criteria:
DELETE Table1
FROM Table2
WHERE Table1.JoinColumn = Table2.JoinColumn And Table1.SomeStuff = 'SomeStuff'
Found this link useful
Copied from there
Oftentimes, one wants to delete some records from a table based on criteria in another table. How do you delete from one of those tables without removing the records in both table?
DELETE DeletingFromTable
FROM DeletingFromTable INNER JOIN CriteriaTable
ON DeletingFromTable.field_id = CriteriaTable.id
WHERE CriteriaTable.criteria = "value";
The key is that you specify the name of the table to be deleted from as the SELECT. So, the JOIN and WHERE do the selection and limiting, while the DELETE does the deleting. You're not limited to just one table, though. If you have a many-to-many relationship (for instance, Magazines and Subscribers, joined by a Subscription) and you're removing a Subscriber, you need to remove any potential records from the join model as well.
DELETE subscribers, subscriptions
FROM subscribers INNER JOIN subscriptions
ON subscribers.id = subscriptions.subscriber_id
INNER JOIN magazines
ON subscriptions.magazine_id = magazines.id
WHERE subscribers.name='Wes';
Deleting records with a join could also be done with a LEFT JOIN and a WHERE to see if the joined table was NULL, so that you could remove records in one table that didn't have a match (like in preparation for adding a relationship.) Example post to come.
Since the OP does not ask for a specific DB, better use a standard compliant statement.
Only MERGE is in SQL standard for deleting (or updating) rows while joining something on target table.
merge table1 t1
using (
select t2.ID
from table2 t2
) as d
on t1.ID = d.ID
when matched then delete;
MERGE has a stricter semantic, protecting from some error cases which may go unnoticed with DELETE ... FROM. It enforces 'uniqueness' of match : if many rows in the source (the statement inside using) match the same row in the target, the merge must be canceled and an error must be raised by the SQL engine.
To Delete table records based on another table
Delete From Table1 a,Table2 b where a.id=b.id
Or
DELETE FROM Table1
WHERE Table1.id IN (SELECT Table2.id FROM Table2)
Or
DELETE Table1
FROM Table1 t1 INNER JOIN Table2 t2 ON t1.ID = t2.ID;
I often do things like the following made-up example. (This example is from Informix SE running on Linux.)
The point of of this example is to delete all real estate exemption/abatement transaction records -- because the abatement application has a bug -- based on information in the real_estate table.
In this case last_update != nullmeans the account is not closed, and res_exempt != 'p' means the accounts are not personal property (commercial equipment/furnishings).
delete from trans
where yr = '16'
and tran_date = '01/22/2016'
and acct_type = 'r'
and tran_type = 'a'
and bill_no in
(select acct_no from real_estate where last_update is not null
and res_exempt != 'p');
I like this method, because the filtering criteria -- at least for me -- is easier to read while creating the query, and to understand many months from now when I'm looking at it and wondering what I was thinking.
Referencing MSDN T-SQL DELETE (Example D):
DELETE FROM Table1
FROM Tabel1 t1
INNER JOIN Table2 t2 on t1.ID = t2.ID
This is old I know, but just a pointer to anyone using this ass a reference. I have just tried this and if you are using Oracle, JOIN does not work in DELETE statements.
You get a the following message:
ORA-00933: SQL command not properly ended.
While the OP doesn't want to use an 'in' statement, in reply to Ankur Gupta, this was the easiest way I found to delete the records in one table which didn't exist in another table, in a one to many relationship:
DELETE
FROM Table1 as t1
WHERE ID_Number NOT IN
(SELECT ID_Number FROM Table2 as t2)
Worked like a charm in Access 2016, for me.
delete
table1
from
t2
where
table1.ID=t2.ID
Works on mssql