Is is possible to store a mysql subquery somehow, if it will be used again as a subquery? Presumably this would produce cleaner code as well as save parsing overheads.
For example in the following outer join
SELECT * FROM t1
LEFT JOIN (SELECT * FROM t2 WHERE t2.foo=='bar') ON t1.id = t2.id
UNION
SELECT * FROM t1
RIGHT JOIN (SELECT * FROM t2 WHERE t2.foo=='bar') ON t1.id = t2.id
It would be nice not to repeat (SELECT * FROM t2 WHERE t2.foo=='bar').
No, you can't. If MySQL had CTE (Common Table Expressions), you could use this:
WITH tmp AS
(SELECT * FROM t2 WHERE t2.foo = 'bar')
SELECT * FROM t1
LEFT JOIN tmp ON t1.id = tmp.id
UNION
SELECT * FROM t1
RIGHT JOIN tmp ON t1.id = tmp.id
If MySQL had FULL JOIN (which alas, it hasn't either!), you could use this:
SELECT * FROM t1
FULL JOIN (SELECT * FROM t2 WHERE t2.foo = 'bar') tmp
ON t1.id = tmp.id
Of course do it like this
SET #condition := (SELECT * FROM t2 WHERE t2.foo=='bar');
SELECT * FROM t1
LEFT JOIN (#condition) ON t1.id = t2.id
UNION
SELECT * FROM t1
RIGHT JOIN (#condition) ON t1.id = t2.id
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
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
Following is my query.
SELECT * FROM t1 WHERE t1.record_id IN (
SELECT t2.record_id FROM t2
INNER JOIN t3 ON CONCAT(t2.case_number,t2.courtfile_type) = CONCAT(t3.case_number,t3.courtfile_type))
It contain IN constraint which is taking lot of time to extract result from database.Database is huge obviously.
How can I optimize this query?
Try this:
USING JOIN
SELECT DISTINCT t1.*
FROM t1
INNER JOIN t2 ON t1.record_id = t2.record_id
INNER JOIN t3 ON t2.case_number = t3.case_number AND t2.courtfile_type = t3.courtfile_type
USING EXISTS
SELECT *
FROM t1
WHERE EXISTS (SELECT t2.record_id
FROM t2 INNER JOIN t3 ON t2.case_number = t3.case_number AND t2.courtfile_type = t3.courtfile_type
WHERE t1.record_id = t2.record_id )
Check the execution plan of the query using EXPLAIN keyword and do proper indexing on tables.
I have a query which contains a select statement in it's where clause. My question is now, how can I access the parent's select's data.
Example:
select * from TABLE_1 as t1 INNER JOIN TABLE_2 as t2
where (... and ...) OR
(not exists(select * from TABLE_3 as t3
inner join TABLE_1 ON t3.t1_id = t1.id
The last line is where the error occurs: t1.id is not a column.
How can I access the current value from the table t1?
I'm using MySql 5.1
SELECT
*
FROM
TABLE_1 as t1
INNER JOIN TABLE_2 as t2 ON
t2.PK = t1.FK --Whatever your keys are
WHERE
(... and ...)
OR
(
NOT EXISTS (select * from TABLE_3 as t3 WHERE t3.t1_id = t1.id)
)
First of all, you need to declare what you will JOIN TABLE_2 on TABLE_1.
SELECT *
FROM TABLE_1 AS t1
INNER JOIN TABLE_2 AS t2 ON t2.t1_id = t1.id
t1.id = t2.t1_id is just an example, you will need to decide which columns you wish you join on. Then in your WHERE clause, you do not need to INNER JOIN on TABLE_1 again as you are already selecting from it.
SELECT *
FROM TABLE_1 AS t1
INNER JOIN TABLE_2 AS t2 ON t2.t1_id = t1.id
WHERE (... AND ...) OR
(
NOT EXISTS
(
SELECT *
FROM TABLE_3 AS t3
WHERE t3.t1_id = t1.id
)
)
Query 1:
SELECT if(COUNT(0),1,0) as 'IsPresent'
FROM table1
WHERE Id=1500;
Query2:
If IsPresent is 1, then
select t2.mark,t2.age from table2 t2,table1 t1
where t1.ID=t2.ID order by t1.ID;
If IsPresent is 0, then
select mark,age from table2;
ie. if entry is present in a table, i need to join else i don't need to join.
Is there any way we can achieve this with a single mysql select query?
I think you can union the two different query cases which would look like:
SELECT T2.MARK, T2.AGE
FROM TABLE1 T1, TABLE2 T2
WHERE
T1.ID=T2.ID AND
T1.ID=1500
UNION
SELECT MARK, AGE
FROM TABLE1
WHERE
NOT ID=1500
SELECT t2.mark, t2.age
FROM table2 t2
JOIN table1 t1
ON t1.id = t2.id
WHERE EXISTS
( SELECT *
FROM table1
WHERE id=1500
)
UNION ALL
SELECT t2.mark, t2.age
FROM table2 t2
WHERE NOT EXISTS
( SELECT *
FROM table1
WHERE id=1500
)
which can be simplified to:
SELECT t2.mark, t2.age
FROM table2 t2
LEFT JOIN table1 t1
ON t1.id = t2.id
AND EXISTS
( SELECT *
FROM table1
WHERE id=1500
)