I have Two tables :
Table1, Table2
I have to write a SQL query which has inner join on three columns based
on <> 0 condition
on these tables.
My condition is
if(table1.ID != 0), then inner join on table1.ID = table2.ID else,
if(table1.MemberID != 0), then inner join on table1.MemberID = table2.MemberID else,
inner join on table1.PersonID = table2.PersonID
You can use a conditional statement (case when for example) in a join clause.
select t1.*, t2.*
from table1 t1
inner join table2 t2 on
(case when
t1.ID != 0
then t1.ID =t2.Id
else
case when t1.MemberId !=0
then t1.MemberId = t2.MemberId
else
t1.PersonId = t2.PersonId
end
end)
see SqlFiddle
This should work.
select *
from Table1, Table2
where table1.Personid = table2.personId
and (((Table1.id != 0) and (Table1.id = table2.Id))
or ((Table1.memberid != 0) and (Table1.memberid = table2.memberId)))
Related
table2.A = 1 for display only
table2.B = 2 for display only
SELECT * FROM table1
INNER JOIN table2 ON
IF(A > B)
table2.id = table1.id -- if value of A is > B then inner join table on table2.id = table1.id
ELSE IF (A < B)
table2.id = table1.somethingElse -- if value of A is < B then inner join table on table2.id = table1.somethingElse
How can i translate this into actual SQL?
Use AND/OR logic in the ON clause:
SELECT *
FROM table1 t1
INNER JOIN table2 t2
ON (t2.A > t2.B AND t1.id = t2.id) OR
(t2.A < t2.B AND t1.somethingElse = t2.id);
Note that your intended logic leaves open an edge case where A = B exactly. Assuming you want to include this, one way would be to change one of the inequalities to either >= or <=.
You can do it with a CASE expression:
SELECT *
FROM table1
INNER JOIN table2 ON table2.id = CASE
WHEN (A > B) THEN table1.id
WHEN (A < B) THEN table1.somethingElse
END
Note that this query still can use an index on table2(id).
It's also possible to use nested IF() functions:
SELECT *
FROM table1
INNER JOIN table2 ON
table2.id = IF(A > B, table1.id, IF(A < B, table1.somethingElse, NULL))
But that's not very readable.
Also note, that in both queries there will be no match if A = B. But that is what your "pseudo code" suggests.
I'm not sure if I understand what exactly do you need. But probably something like this. It's in PostgreSQL.
SELECT *
FROM
table1
INNER JOIN table2 ON
CASE WHEN table1.A > table2.B THEN table1.id = table2.id
ELSE table1.id = table2.id2
END;
I try to establish a conditional 'on clause' in a mysql join.
If field1 is not empty, this should be used in the 'on claus',
but if empty, field2 instead should be used.
SELECT * FROM table1
JOIN table2
IF (field1!='') THEN (
ON table1.field1 = table2.field1
AND table1.field3 = table2.field3
)
ELSE (
ON table1.field2 = table2.field2
AND table1.field3 = table2.field3
)
END IF
Any idea if this is possible on how it could be done?
Edit:
I forgot to explain that both tables contain empty fields and I try to prevent that mysql uses these fields for the join, as that gives a (very) lot of joins, so my idea should be more like this:
SELECT * FROM table1
JOIN table2
IF (table1.field1!='' AND table2.field1!='') THEN (
ON table1.field1 = table2.field1
AND table1.field3 = table2.field3
)
ELSE (
ON table1.field2 = table2.field2
AND table1.field3 = table2.field3
)
END IF
Try this instead:
SELECT * FROM table1 t1
LEFT JOIN table2 t2
LEFT JOIN table2 t3
on t1.Field1=t2.Field1 and t1.Field3=t2.Field3
on t1.Field2=t3.Field2 and t1.Field3=t3.Field3
Then use a condition tho choose the field from table2 or table3.
Hope this helps you.
EDIT
To select the right field use this:
SELECT t1.*, IF(t2.field1 is null, t3.field1, t2.Field1) as Field1
I think you can do something like this:
SELECT * FROM table1
JOIN table2 ON
(
(table1.field1 = '' AND table1.field2 = table2.field2 AND table1.field3 = table2.field3)
OR
(table1.field1 != '' AND table1.field1 = table2.field1 AND table1.field3 = table2.field3)
)
(note: I have no idea how efficient or otherwise this approach is)
You should consider converting your INNER JOIN to a LEFT JOIN as already shown in other answer like
SELECT * FROM table1 t1
LEFT JOIN table2 t2
ON t1.field1 = t2.field1 AND t1.field3 = t2.field3
LEFT JOIN table2 t22
ON t1.field2 = t22.field2 AND t1.field3 = t22.field3
You can as well try something like below
SELECT t1.*
FROM table1 t1
JOIN table2 t2
ON t1.field1 = t2.field1 AND t1.field3 = t2.field3
OR t1.field2 = t2.field2 AND t1.field3 = t2.field3
I'm trying to inner join table1 <- to -> table2, table3, table4 OR table5 depending on a field present in table1. So, if the field information in table1 has the value example_get_from_two I should inner join table1 with table2 as to obtain a given row, if in another row table1 has the value example_get_from_three I should inner join table1 with table3 and so on. This is the query I tried, but it returned zero rows:
SELECT n.notification_type,
(CASE WHEN n.notification_type = 'two' AND n.information = t2.somefield
THEN t2.anotherfield
WHEN n.notification_type = 'three'
THEN (CASE WHEN t3.field = '1' THEN t3.otherfield ELSE t3.yetanotherfield END)
WHEN n.notification_type = 'four' AND t4.field = n.information
THEN t4.anotherfield
WHEN n.notification_type = 'five'
THEN t5.field
END) AS information FROM table0 zero, notifications n
INNER JOIN table1 t1 ON(n.information=t1.somefield AND n.notification_type = 'something')
INNER JOIN table2 t2 ON(n.information=t2.somefield AND n.notification_type = 'something')
INNER JOIN table3 t3 ON((n.information=t3.somefield OR n.information=t3.someotherfield) AND n.notification_type = 'something')
WHERE zero.field ='something' AND n.id = zero.id
Unfortunately this retrieves zero rows and shouldn't , probably because all joins are made despite the actual value of information, and n.notification_type = "something". Is this possible with cases or similar? What I'd like to obtain is
fromfield1 | fromfield2 | fromfield3 (this one is "dynamic" and
depends on the joined table)
I have been using the following SQL:
SELECT DISTINCT NAME
FROM Events t1
LEFT JOIN UserHistory t2 ON t1.Name = t2.Event
WHERE t2.Event IS NULL
To select all rows from table 1 where table 2 is Null. This effectively filters out all my Table 1 data where Table 2 has data. However, I want to apply this only when a column in table 2 equals a certain value. Therefore I am looking to do a SELECT * FROM t2 WHERE t2.ID = 1 but am unsure how this fits into this query.
SELECT DISTINCT NAME
FROM Events t1
LEFT JOIN UserHistory t2 ON t1.Name = t2.Event and t2.certain_column = 1234
WHERE t2.Event IS NULL
Also you can try query with NOT EXISTS:
SELECT DISTINCT NAME
FROM Events t1
WHERE NOT EXISTS(SELECT * FROM UserHistory t2
WHERE t1.Name = t2.Event AND t2.ID = 1)
You need to add the predicate to the JOIN condition:
SELECT DISTINCT NAME
FROM Events t1
LEFT JOIN UserHistory t2 ON t1.Name = t2.Event AND t2.ID = 1
WHERE t2.Event IS NULL;
If you add it to the WHERE you effectively turn your outer join into an inner join, meaning no rows will be returned (since NULL = 1 evaluates to false)
SELECT
count(t1.id) AS c1
FROM
table2
LEFT JOIN table1 AS t1 ON (t1.uid = table2.uid)
WHERE
table2.mode = 'ls'
GROUP BY
t1.id
c1 = 6 -> CORRECT!
SELECT
count(t2.id) AS c2
FROM
table2
LEFT JOIN table1 AS t2 ON (t2.pid = table2.id)
WHERE
table2.mode = 'ls'
GROUP BY
t1.id
c2 = 1 -> CORRECT!
SELECT
count(t1.id) AS c1,
count(t2.id) AS c2
FROM
table2
LEFT JOIN table1 AS t1 ON (t1.uid = table2.uid)
LEFT JOIN table1 AS t2 ON (t2.pid = table2.id)
WHERE
table2.mode = 'ls'
GROUP BY
t1.id
c1 = 6 -> CORRECT!
c2 = 6 -> WRONG!
How do I request both counts in one query, without getting wrong results?
I need to count two different requests at the same table (table1).
so, I'm using an alias for both request. (t1). Each alias-request is working fine alone. If I use both in the same query, i got wrong results.
count() will get you the number of records that are returned by your query. Since if you removed the counts and replaced it with * you would have 6 rows both of those counts are giving you 6.
Is there any reason why you cant use two sub selects and return the result of each of those?
So:
SELECT subQ1.c1, subQ2.c2 FROM
(SELECT count(t1.id) AS c1 FROM table2
LEFT JOIN table1 AS t1 ON (t1.uid = table2.uid)
WHERE table2.mode = 'ls') as subQ1,
(SELECT count(t2.id) AS c2 FROM table2
LEFT JOIN table1 AS t2 ON (t2.pid = table2.id)
WHERE table2.mode = 'ls') as SubQ2;
I believe your problem on the full query is your group by function. You are grouping by t.id, thus a1.id will have a different count based on how many rows you have.
What I mean by this is if there are 6 rows in table t, then count is going to return 6 for table t; but also since there looks to be a 1 to 1 relation on table a, there are 6 matching rows in table a to the 6 matching rows in table t. such that
t.id = a.id
1 = 1
2= 2 ...etc.
Thus your count is returning rows versus the count you believe you should have? I believe sum function is what you want to use here.
You could try this...but I'm not really sure what you're trying to do.
SELECT (...)
count(CASE WHEN t1.uid = t3.uid THEN t1.id ELSE NULL END) AS CBanz,
count(CASE WHEN ta1.pid = t3.id THEN a1.id ELSE NULL END) AS CBanz1
FROM
t0
LEFT JOIN (...)
LEFT JOIN t1 ON (t1.uid = t3.uid)
LEFT JOIN t1 AS a1 ON (a1.pid = t3.id)
WHERE (...)