I have these MySQL tables:
table1:
id | writer
1 | Bob
2 | Marley
3 | Michael
table2:
user_one | user_two
1 | 2
And this query:
SELECT table1.id FROM table1 LEFT JOIN table2 ON table1.id = table2.user_one
This query will return all rows of table1 which are 1,2,3
I want to select only rows which are not found in the left joint. So it should return only row with id 3
I want sort of the opposite of INNER JOIN which will select only the rows which are found in the join. How to get the opposite like if left join exists, ignore it and move to the next row. Hope i'm clear
You could use the following query:
SELECT table1.id
FROM table1
LEFT JOIN table2
ON table1.id IN (table2.user_one, table2.user_two)
WHERE table2.user_one IS NULL;
Although, depending on your indexes on table2 you may find that two joins performs better:
SELECT table1.id
FROM table1
LEFT JOIN table2 AS t1
ON table1.id = t1.user_one
LEFT JOIN table2 AS t2
ON table1.id = t2.user_two
WHERE t1.user_one IS NULL
AND t2.user_two IS NULL;
One of the best approach if you do not want to return any columns from table2 is to use the NOT EXISTS
SELECT table1.id
FROM table1 T1
WHERE
NOT EXISTS (SELECT *
FROM table2 T2
WHERE T1.id = T2.user_one
OR T1.id = T2.user_two)
Semantically this says what you want to query: Select every row where there is no matching record in the second table.
MySQL is optimized for EXISTS: It returns as soon as it finds the first matching record.
One more note to this:
When you check against a nullable column in the joined table, depending on your needs, you may have to use NOT EXISTS (or check against other columns when using LEFT JOIN), because MySQL won't be able to distinguish between a column which is NULL, but there is an existing record in the joined table and a column which is generated as NULL because the joined table have no matching record.
Here is a query that returns only the rows where no correspondance has been found in both columns user_one and user_two of table2:
SELECT T1.*
FROM table1 T1
LEFT OUTER JOIN table2 T2A ON T2A.user_one = T1.id
LEFT OUTER JOIN table2 T2B ON T2B.user_two = T1.id
WHERE T2A.user_one IS NULL
AND T2B.user_two IS NULL
There is one jointure for each column (user_one and user_two) and the query only returns rows that have no matching jointure.
Hope this will help you.
SELECT table1.id
FROM table1
LEFT JOIN table2 ON table1.id = table2.user_one
WHERE table2.user_one is NULL
Try following query:-
SELECT table1.id
FROM table1
where table1.id
NOT IN (SELECT user_one
FROM Table2
UNION
SELECT user_two
FROM Table2)
Hope this helps you.
Try:
SELECT A.id FROM
(
SELECT table1.id FROM table1
LEFT JOIN table2 ON table1.id = table2.user_one
WHERE table2.user_one IS NULL
) A
JOIN (
SELECT table1.id FROM table1
LEFT JOIN table2 ON table1.id = table2.user_two
WHERE table2.user_two IS NULL
) B
ON A.id = B.id
See Demo
Or you could use two LEFT JOINS with aliases like:
SELECT table1.id FROM table1
LEFT JOIN table2 A ON table1.id = A.user_one
LEFT JOIN table2 B ON table1.id = B.user_two
WHERE A.user_one IS NULL
AND B.user_two IS NULL
See 2nd Demo
Related
I have three tables with following data
Table 3 :
Table1_id Table2_id
1 1
1 2
1 3
2 1
2 3
3 2
Table 2 :
Table2_id Name
1 A
2 B
3 C
Table 1 :
Table1_id Name
1 P
2 Q
3 R
I have a problem where I need to return all table1_id's which have an entry for all Table2_ids's in Table 3.
ie. I want my output to be
Table1_id
1
I found a solution using count().
But is there a way to use all() or exists() to solve the query?
Using NOT IN with excluding LEFT JOIN in a subselect with a CROSS JOIN
select *
from table1
where Table1_id not in (
select t1.Table1_id
from table1 t1
cross join table2 t2
left join table3 t3 using (Table1_id, Table2_id)
where t3.Table1_id is null
)
VS using COUNT()
select table1_id
from table3
group by table1_id
having count(1) = (select count(1) from table2)
Explanation:
The CROSS JOIN
select t1.Table1_id
from table1 t1
cross join table2 t2
represents how table3 would look like, if every item from table1 would be related to every item from table2.
A (natural) left join with table3 will show us which relations really exists. Filtering by where t3.Table1_id is null (excluding LEFT JOIN) we get the missing relations. Using that result for the NOT IN clause, we get only table1 items that have no missing relation with table2.
You can use the following query:
SELECT DISTINCT t1.*
FROM Table2 AS t2
CROSS JOIN Table1 AS t1
WHERE NOT EXISTS (SELECT 1
FROM Table3 AS t3
WHERE t1.Table1_id = t3.Table1_id AND
t2.Table2_id = t3.Table2_id)
to get Table1 records not having a complete set of entries from Table2 in Table3. Then use NOT IN to get the expected result.
Here is a solution using EXISTS and INNER JOIN.
SELECT DISTINCT t3_out.Table1_id FROM Table3 t3_out
WHERE EXISTS( SELECT 1
FROM Table2 t2 INNER JOIN Table3 t3 ON t2.Table2_id = t3.Table2_id
WHERE t3.Table1_id = t3_out.Table1_id
HAVING COUNT(DISTINCT t2.Table2_id) = 3 )
Lets say I have 2 tables:
table1
table1_id
table1_name
table2
table2_id
table2_name
table2_description
table1_id
I join like so:
SELECT * FROM table1 LEFT JOIN table2 ON table1.table1_id = table2.table1_id
How can I have table1_id return its default value instead of NULL when there are no matches in table2?
Answer: Since table1_id exists in both tables, I needed to used aliases.
SELECT *, table1.table1_id AS tid, table2.table1_id AS t2id FROM table1 LEFT JOIN table2 ON table1.table1_id = table2.table1_id
If I understand correctly, you bring in the default row and then use logic in the select:
SELECT t1.*,
COALESCE(t2.table2_name, t2def.table2_name) as table2_name,
. . .
FROM table1 t1 LEFT JOIN
table2 t2
ON t1.table1_id = t2.table1_id LEFT JOIN
table2 t2def
ON t2def.table1_id = $defaultid;
SELECT table1.*
table2.table2_id,
table2.table2_name,
table2.table2_description,
ifnull(table2.table1_id, table1.table1_id) t2id
FROM table1 LEFT JOIN table2
ON table1.table1_id = table2.table1_id
Again, there is no point to check if table2.table1_id is null, as it is the join column ... always either NULL or exactly same as table1.table1_id
I have these MySQL tables:
table1:
id | writer
1 | Bob
2 | Marley
3 | Michael
table2:
user_one | user_two
1 | 2
And this query:
SELECT table1.id FROM table1 LEFT JOIN table2 ON table1.id = table2.user_one
This query will return all rows of table1 which are 1,2,3
I want to select only rows which are not found in the left joint. So it should return only row with id 3
I want sort of the opposite of INNER JOIN which will select only the rows which are found in the join. How to get the opposite like if left join exists, ignore it and move to the next row. Hope i'm clear
You could use the following query:
SELECT table1.id
FROM table1
LEFT JOIN table2
ON table1.id IN (table2.user_one, table2.user_two)
WHERE table2.user_one IS NULL;
Although, depending on your indexes on table2 you may find that two joins performs better:
SELECT table1.id
FROM table1
LEFT JOIN table2 AS t1
ON table1.id = t1.user_one
LEFT JOIN table2 AS t2
ON table1.id = t2.user_two
WHERE t1.user_one IS NULL
AND t2.user_two IS NULL;
One of the best approach if you do not want to return any columns from table2 is to use the NOT EXISTS
SELECT table1.id
FROM table1 T1
WHERE
NOT EXISTS (SELECT *
FROM table2 T2
WHERE T1.id = T2.user_one
OR T1.id = T2.user_two)
Semantically this says what you want to query: Select every row where there is no matching record in the second table.
MySQL is optimized for EXISTS: It returns as soon as it finds the first matching record.
One more note to this:
When you check against a nullable column in the joined table, depending on your needs, you may have to use NOT EXISTS (or check against other columns when using LEFT JOIN), because MySQL won't be able to distinguish between a column which is NULL, but there is an existing record in the joined table and a column which is generated as NULL because the joined table have no matching record.
Here is a query that returns only the rows where no correspondance has been found in both columns user_one and user_two of table2:
SELECT T1.*
FROM table1 T1
LEFT OUTER JOIN table2 T2A ON T2A.user_one = T1.id
LEFT OUTER JOIN table2 T2B ON T2B.user_two = T1.id
WHERE T2A.user_one IS NULL
AND T2B.user_two IS NULL
There is one jointure for each column (user_one and user_two) and the query only returns rows that have no matching jointure.
Hope this will help you.
SELECT table1.id
FROM table1
LEFT JOIN table2 ON table1.id = table2.user_one
WHERE table2.user_one is NULL
Try following query:-
SELECT table1.id
FROM table1
where table1.id
NOT IN (SELECT user_one
FROM Table2
UNION
SELECT user_two
FROM Table2)
Hope this helps you.
Try:
SELECT A.id FROM
(
SELECT table1.id FROM table1
LEFT JOIN table2 ON table1.id = table2.user_one
WHERE table2.user_one IS NULL
) A
JOIN (
SELECT table1.id FROM table1
LEFT JOIN table2 ON table1.id = table2.user_two
WHERE table2.user_two IS NULL
) B
ON A.id = B.id
See Demo
Or you could use two LEFT JOINS with aliases like:
SELECT table1.id FROM table1
LEFT JOIN table2 A ON table1.id = A.user_one
LEFT JOIN table2 B ON table1.id = B.user_two
WHERE A.user_one IS NULL
AND B.user_two IS NULL
See 2nd Demo
I'm trying to search a rows of table3 that have id match in a table1 OR table2 with this query
SELECT T1.*, T3.*,T2.*
FROM (
select id
from table1
where condition like '%field%') T1
inner join table3 T3
ON T3.id=T1.id
left join (
select id
from table2
where condition like '%field%') T2
ON T3.id=T2.id
If in table T1 have matches but in table2 not, the query works fine but if in table1 not have matches but have in table2 the query not show any results.
Someone can help me?
Thanks
do left join to avoid excluding rows, and add a where with the condition you need FOr readability sake,avoid right joins and jsut use proper table order
SELECT T1.*, T3.*,T2.*
FROM Table3 T3
left join (
select id
from table1
where condition like '%field%') T1
ON T3.id=T1.id
left join (
select id
from table2
where condition like '%field%') T2
ON T3.id=T2.id
where t3.id is not null or t2.id is not null
Table1: ID,Name,some more columns
Table2: ID
Table3: Name
I want get output from table1, whose IDs are present in Table2.IDs & whose Name are present in Table3.Name.
In other words, select data which is present in ALL the 3 tables.
For ex:
Table1:
1 John
2 Will
3 Michael
Table2:
1
Table3:
Will
The output should be
1 John
2 Will
You need to use JOINs.
Your description and your sample output do not match, so I'll give you one example for each.
Based on your description, it should be 2 INNER JOINs:
select table1.id, table1.name
from table1
inner join table2 on table2.id = table1.id
inner join table3 on table3.name = table1.name
Based on your output, it should be 2 OUTER JOINS with a WHERE clause specifying that at least one of the 2 joins was satisfied:
select table1.id, table1.name
from table1
left outer join table2 on table2.id = table1.id
left outer join table3 on table3.name = table1.name
where table2.id is not null or table3.name is not null
Based on your expected results, it looks like you want rows from Table1 that match either Table2 OR Table3, so you'll want to use LEFT JOINs.
select t1.ID, t1.Name
from Table1 t1
left join Table2 t2
on t1.ID = t2.ID
left join table3 t3
on t1.Name = t3.Name
where t2.ID is not null
or t3.Name is not null