Lets suppose I have a full outer join query written in these styles:
SELECT * FROM Table_A
FULL OUTER JOIN Table_B ON (Table_A.Col1 = Table_B.Col1 AND Table_B.iscurrent=1)
Versus
SELECT * FROM Table_A
FULL OUTER JOIN (Select * FROM Table_B Where iscurrent=1) AS Table_B
ON (Table_A.Col1 = Table_B.Col1)
Both are producing different results in my database (Azure SQL DB).
How come?
Why are they returning different results? Because they are different queries. FULL OUTER JOIN is very tricky. Let me explain.
The result set from the first query has rows from all the rows in both tables, even those where Table_B.iscurrent <> 1. If this is not true, then the corresponding columns will be NULL, but the row will be there.
The result set from the second query will have no rows were Table_B.iscurrent <> 1. These are filtered out before the FULL OUTER JOIN, so they are not among the rows being counted.
In general, I find that FULL OUTER JOIN is very rarely needed. I do use it, but quite rarely. Typically LEFT JOIN or UNION ALL does what I really want.
On the second only rows with Where Table_B.iscurrent = 1 are included.
In the first you have all the rows in Table_B but they just don't connect to Table_A if iscurrent <> 1.
SELECT *
FROM Table_A
FULL OUTER JOIN Table_B
ON Table_A.Col1 = Table_B.Col1
AND Table_B.iscurrent = 1
SELECT *
FROM Table_A
FULL OUTER JOIN ( Select *
FROM Table_B
Where iscurrent = 1
) AS Table_B
ON Table_A.Col1 = Table_B.Col1
Related
I'd like to implement an antijoin on two table but using two keys so that the result is all rows in Table A that do not contain the combinations of [key_1, key_2] found in Table B. How can I write this query in SQL?
If you want an anti-left join, the logic is:
select a.*
from tablea a
left join tableb b on b.key_1 = a.key_1 and b.key_2 = a.key_2
where b.key_1 is null
As for me, I like to implement such logic with not exists, because I find that it is more expressive about the intent:
select a.*
from tablea a
where not exists (
select 1 from tableb b where b.key_1 = a.key_1 and b.key_2 = a.key_2
)
The not exists query would take advantage of an index on tableb(key_1, key_2).
select a.*
from table_a a
left anti join table_b b on a.key_1 = b.key_1 and a.key_2 = b.key_2;
These queries both get results:
SELECT * FROM Table1 WHERE Criteria = '5'
SELECT * FROM Table1 WHERE Criteria = '3'
This query gets results:
SELECT *
FROM Table1 p, Table2 m
WHERE p.UID = m.ID
AND Criteria = '5'
This query does not:
SELECT *
FROM Table1 p, Table2 m
WHERE p.UID = m.ID
AND Criteria = '3'
I am trying to convert these to a proper join which returns results even if there are no records in the right table.
I have tried the following
SELECT *
FROM Table1 p LEFT JOIN Table2 m ON p.UID = m.ID
WHERE p.Criteria = '3'
AND m.OtherCriteria = 'Moron'
--0 results
My limited understanding was that LEFT join is what I needed. I want data from the left table even if there is no data in the right table that matches. Since this didn't work I also tried right join, left outer join, right outer join and full join. None returned results.
What am I missing?
This is too long for a comment. Your query:
SELECT *
FROM Table1 p LEFT JOIN
Table2 m
ON p.UID = m.ID AND p.Criteria = '3';
Should be returning a row for all rows in table1. If there is no match, then the values will be NULL for table2. This is easily demonstrated: Here is a MySQL example on SQL Fiddle. Because this is standard behavior, it should work on almost any database.
Note that this query is quite different from this one:
SELECT *
FROM Table1 p LEFT JOIN
Table2 m
ON p.UID = m.ID
WHERE p.Criteria = '3';
This query returns no rows, because no rows match the WHERE clause. The filtering happens (conceptually) after the LEFT JOIN.
I changed the code in the SQL Fiddle slightly, so that query is:
select *
from (select 5 as criteria, 1 as id union all
select 6, 1 union all
select 7, 2
) table1 left join
(select 1 as id, 'x' as x
) table2
on table1.id = table2.id and criteria = 3;
As a note: you should always use explicit join syntax. Simple rule: Never use commas in the FROM clause.
If your database is returning no rows, then it is behaving in a non-standard manner or your interface has decided to filter the rows for some reason.
please help on below query
select * from processed_h where c_type not in (select convert(int,n_index) from index_m where n_index <>'0') **-- 902 rows**
select * from processed_h where c_type not in (2001,2002,2003) **-- 902 rows**
select convert(int,n_index) from index_m where n_index <>'0' **--- 2001,2002,2003**
I tried to convert the not in to LEFT JOIN as below but it is giving me 40,000 rows returned what I am doing wrong
select A.* from processed_h A LEFT JOIN index_m B on A.c_type <> convert(int,B.n_index) and B.n_index <>'0' --40,000 + rows
A LEFT JOIN returns ALL rows from the "left-hand" table regardless of whether the condition matches or not, which is why you are getting the "extra" rows.
An INNER JOIN might give you the same number of rows, but if there are multiple matches in the "right-hand" table then you'll still get more rows than you expect.
If NOT IN gives you the expected results then I'd stick with that. You probably aren;t going to see significant improvements with a join. The only reason I would change to an INNER JOIN is if I needed columns from the joined table in my output.
For the equivalent of a NOT IN using a left join, you need to link the tables as though the results in the linked table should be IN the resultset, then select only those records where the outer joined table did not return a record - like so:
select A.* from processed_h A
LEFT JOIN index_m B on A.c_type = convert(int,B.n_index) and B.n_index <>'0'
WHERE B.n_index IS NULL
However, you might get better performance using a NOT EXISTS query instead:
select A.* from processed_h A
where not exists
(select 1 from index_m B where B.n_index <>'0' and A.c_type = convert(int,B.n_index) )
I have a join on two tables defined as a left outer join so that all records are returned from the left hand table even if they don't have a record in the right hand table. However I also need to include a where clause on a field from the right-hand table, but.... I still want a row from the left-hand table to be returned for each record in the left-hand table even if the condition in the where clause isn't met. Is there a way of doing this?
Yes, put the condition (called a predicate) in the join conditions
Select [stuff]
From TableA a
Left Join TableB b
On b.Pk = a.Pk
-- [Put your condition here, like this]
And b.Column = somevalue
The reason this works is because the query processor applies conditions in a where clause after all joins are completed, and the final result set has been constructed. So, at that point, a column from the a table on the outer side of a join that has null in a a column you have established a predicate on will be excluded.
Predicates in a join clause are applied before the two result sets are "joined". At this point all the rows on both sides of the join are still there, so the predicate is effective.
You just need to put the predicate into the JOIN condition. Putting it into the WHERE clause would effectively convert your query to an inner join.
For Example:
...
From a
Left Join b on a.id = b.id and b.condition = 'x'
You can use
WHERE (right_table.column=value OR right_table.column IS NULL)
This will return all rows from table 1 and table 2, but only where table 1 does not have a corresponding row in table 2 or the corresponding row in table 2 matches your criteria.
SELECT x.fieldA, y.fieldB
FROM x
LEFT OUTER JOIN (select fieldb, fieldc from Y where condition = some_condition)
ON x.fieldc = y.fieldc
select *
from table1 t1
left outer join table2 t2 on t1.id = t2.id
where t1.some_field = nvl(t2.some_field, t1.some_field)
UPD: errr... no. this way:
select *
from table1 t1
left outer join table2 t2 on t1.id = t2.id
where some_required_value = nvl(t2.some_field, some_required_value)
nvl is an Oracle syntax which replaces first argument with second in case it is null (which is common for outer joins). You can use ifnull or coalesce for other databases.
Thus, you compare t2.some_field with your search criteria if it has met join predicate, but if it has not, then you just return row from table1, because some_required_value compared to itself will always be true (unless it is null, however - null = null yields null, neither true not false.
Hi I have 2 tables. I want to list
all records in table1 which are present in
table2
all records in table2 which are not present in table1 with a where condition
Null rows will be returned by table1 in second condition but I am unable to get the query working correctly. It is only returning null rows
SELECT
A.CLMSRNO,A.CLMPLANO,A.GENCURRCODE,A.CLMNETLOSSAMT,
A.CLMLOSSAMT,A.CLMCLAIMPRCLLOSSSHARE
FROM
PAKRE.CLMCLMENTRY A
RIGHT OUTER JOIN (
SELECT
B.CLMSRNO,B.UWADVICETYPE,B.UWADVICENO,B.UWADVPREMCURRCODE,
B.GENSUBBUSICLASS,B.UWADVICENET,B.UWADVICEKIND,B.UWADVYEAR,
B.UWADVQTR,B.ISMANUAL,B.UWCLMNOREFNO
FROM
PAKRE.UWADVICE B
WHERE
B.ISMANUAL=1
) r
ON a.CLMSRNO=r.CLMSRNO
ORDER BY
A.CLMSRNO DESC;
Which OS are you using ?
Table aliases are case sensistive on some platforms, which is why your join condition ON a.CLMSRNO=r.CLMSRNO fails.
Try with A.CLMSRNO=r.CLMSRNO and see if that works
I'm not understanding your first attempt, but here's basically what you need, I think:
SELECT *
FROM TABLE1
INNER JOIN TABLE2
ON joincondition
UNION ALL
SELECT *
FROM TABLE2
LEFT JOIN TABLE1
ON joincondition
AND TABLE1.wherecondition
WHERE TABLE1.somejoincolumn IS NULL
I think you may want to remove the subquery and put its columns into the main query e.g.
SELECT A.CLMSRNO, A.CLMPLANO, A.GENCURRCODE, A.CLMNETLOSSAMT,
A.CLMLOSSAMT, A.CLMCLAIMPRCLLOSSSHARE,
B.CLMSRNO, B.UWADVICETYPE, B.UWADVICENO, B.UWADVPREMCURRCODE,
B.GENSUBBUSICLASS, B.UWADVICENET, B.UWADVICEKIND, B.UWADVYEAR,
B.UWADVQTR, B.ISMANUAL, B.UWCLMNOREFNO
FROM PAKRE.CLMCLMENTRY A
RIGHT OUTER JOIN PAKRE.UWADVICE B
ON A.CLMSRNO = B.CLMSRNO
WHERE B.ISMANUAL = 1
ORDER
BY A.CLMSRNO DESC;