see the following SQL..
SELECT t1.*
FROM table1 t1
INNER JOIN table2 t2 ON t1.user_id = t2.id, tables3 t3
WHERE t3.id = 999
what kind of join is there here? between t1 and t3?. I mean what is the comma all about?
A , in the FROM clause is a deprecated shorthand for CROSS JOIN
A better way to write the query is with an explicit CROSS JOIN:
SELECT t1.*
FROM table1 t1 INNER JOIN
table2 t2
ON t1.user_id = t2.id CROSS JOIN
tables3 t3
WHERE t3.id = 999 ;
As written, the query makes no sense. Assuming that t3.id = 999 is true and appears once, then this is equivalent to:
SELECT t1.*
FROM table1 t1 INNER JOIN
table2 t2
ON t1.user_id = t2.id;
If the value doesn't exist, then no rows will be returned.
SELECT t1.*
FROM table1 t1
JOIN table2 t2 ON t1.user_id = t2.id
JOIN tables3 t3 ON t2.id=t3.id
WHERE t3.id = 999
Related
I basically want to join the result of two INNER JOINs.
On this scheme I want to get the three arrows results combined.
I've tried INNER / LEFT combinations but it doesn't do the trick.
I think a nested request could be the solution but how ?
Thanks
The answer was actually simple : UNION
SELECT t1.*
FROM
(SELECT t1.*
FROM table1 t1 JOIN table2 t2 ON t2.id = i.client_id
UNION
SELECT t1.*
FROM t1 t1 JOIN table3 t3 ON t1.id = t3.client_id) as q1
;
I'd use logic to express the condition T1.id exists in T2 or T3 more directly, and certainly avoid use of DISTINCT or UNION.
Options could be to use EXISTS directly (As this is immure to the possibility of duplication cause by 1:many joins)...
SELECT
t1.*
FROM
table1 t1
WHERE
EXISTS (SELECT * FROM table2 t2 WHERE t2.t1_id = t1.id)
OR
EXISTS (SELECT * FROM table3 t3 WHERE t3.t1_id = t1.id)
Or to LEFT JOIN twice and then exclude unwanted rows. (This assumes that the joins are never 1:many, which would introduce duplication, and the unwanted need for a DISTINCT.)
SELECT
t1.*
FROM
table1 t1
LEFT JOIN
table2 t2
ON t1.id = t2.t1_id
LEFT JOIN
table3 t3
ON t1.id = t3.t1_id
WHERE
t2.t1_id IS NOT NULL
OR
t3.t1_id IS NOT NULL
SELECT t1.*, IFNULL(t2.profile_id, t3.profile_id) AS `profile_id`
FROM table1 AS t1
LEFT JOIN table2 AS t2
ON t1.id = t2.some_coulmn
LEFT JOIN table3 AS t3
ON t1.id = t3.some_coulmn
LEFT JOIN table4 AS t4
ON profile_id = t4.some_column
I'm trying to use an alias (profile_id) inside my join condition. It fails. Is there a way to do this?
Column aliases defined in th SELECT clause cannot be used in the join conditions. This is because the FROM clause is evaluated before the SELECT clause.
If I followed you correctly, you probably want:
SELECT t1.*, IFNULL(t2.profile_id, t3.profile_id) AS `profile_id`
FROM table1 AS t1
LEFT JOIN table2 AS t2
ON t1.id = t2.some_coulm
LEFT JOIN table3 AS t3
ON t1.id = t3.some_coulm
LEFT JOIN table4 AS t4
ON IFNULL(t2.profile_id, t3.profile_id) = t4.some_column
I have 2 tables and result as shown in the image below: MySQL DB
What would be best way to join the two tables so we get the result as shown above.
SELECT * FROM (SELECT id, desc FROM table2) as T1
LEFT JOIN (SELECT * FROM table1) as T2 ON T1.id = T2.id
I guess my SQL is not working.
You can use a LEFT JOIN with COALESCE:
SELECT t1.id, COALESCE(t2.desc, t1.desc) AS desc, t1.D1, t1.D2
FROM table1 as T1
LEFT JOIN table2 as T2 ON T1.id = T2.id
Use a left join with coalesce to prioritize table 2's values if they are present, but fallback on table 1's values if not.
select t1.id,
coalesce(t2.desc, t1.desc) as desc,
t1.d1, t1.d2
from table1 t1
left join table2 t2
on t2.id = t1.id
order by t1.id
You can use ifnull:
SELECT t1.id, ifnull(t2.desc, t1.desc) AS desc, t1.D1, t1.D2
FROM table1 as T1
LEFT JOIN table2 as T2 ON T1.id = T2.id
coalesce or case .. when is also possible. All together with the left join
How to select all records in the table t2 which t2.t1_id has no coincidence with t1.id.
SELECT * FROM t2 LEFT JOIN t1 ON t1.id <> t2.t1_id
Any tips, link or code example would be useful.
If what you want is all t2 records without a matching id in t1, but no columns from t1, you could do:
Select * from t2
WHERE t2.t1_id NOT IN(Select id from T1)
This selects all records in t2, but then filters out those that exist in t1 based on t1_id
You can use a not in:
SELECT *
FROM t2
WHERE t2.t1_id not in (select id from t1)
SELECT t2.*
FROM t2
LEFT JOIN t1
ON t1.id = t2.t1_id
where t1.id is null
Just want to add, NOT EXIST is better in most cases:
SELECT *
FROM t2
WHERE NOT EXIST (SELECT 1 FROM t1
WHERE t2.t1_id = t1.id)
Otherwise, you can use NOT IN or LEFT JOIN with NULL
I am trying to find rows if the second query that do not exist in the first. But I get the 'You have error in your SQL syntax near a right join' error.
(SELECT t1.id AS id, t2.id, t3.id
FROM table1 t1
INNER JOIN table2 t2 ON t2.id = t1.id
INNER JOIN table3 t3 ON t3.id = t2.id
) a
RIGHT JOIN
(SELECT id
FROM table4
WHERE col1 IS NOT NULL AND col2 IN (1, 2)) b
ON a.id = b.id
What do I do wrong in this query? Thank you.
In join queries, you must put all your columns in the first select statement. The second select statement in your query is invalid.
SELECT
t1.id as id, t2.id, t3.id, b.id
FROM
(table1 t1
inner join table2 t2 on t2.id=t1.id
inner join table3 t3 on t3.id=t2.id)
right join table4 b on t1.id = b.id
WHERE b.col1 IS NOT NULL AND b.col2 IN (1, 2))