Does mysql got cover IF ELSE to select the table dynamically ?
The link here show's IF THEN is for the value, but how can the IF THEN / IF ELSE can achieve to select the table like below :
For example the dynamic table is 'othertable'
SELECT t1.etc,t2.etc,othertable.etc
FROM table1 AS t1,table2 AS t2, IF(t1.value=3,table3,table4) AS othertable
WHERE othertable.table1_id = t1.id
You could achieve something like this with a union.
SELECT t1.* FROM table1 t1
JOIN table_a ta ON (...)
WHERE t1.value = 3
UNION ALL
SELECT t1.* FROM table1 t1
JOIN table_b tb ON (...)
WHERE t1.value = 2
For each row where t1.value =3, a join with table_a is done, for each row where t1.value = 2, table_b is joined. The union adds the results together.
You just need to make sure that the two conditions are mutually exclusive. If you can't ensure this, you can get rid of duplicates in your result set by using UNION instead of UNION ALL.
Related
The database I am working on right now is somewhat messy. I have three potential tables, that I want to join but in some cases it may only be two tables.
Let's call these table1, table2 and table3.
table1 has a field called "type". If table1.type is 2, then I only need to join table3.
For any other values I want to join table2 and then table3.
How can I achieve this in one single SQL query rather than: 1) having one query to select the type. 2) make a PHP foreach-loop to check the type of the current iteration and 3) perform a new query according to the type value.
Edit:
I'll try to be more specific.
table1 has a column named "pid" that references to a whole other table, but that's redundant to this question. I tried working my ways around with UNIONs and LEFT JOINs but couldn't manage to achieve what I was looking for.
I want to select all results from my database with the "pid" value being "100". This gives me four rows in return, where was 2 of them are of type value "2" and the others are "1".
So basically what I want to achieve is the following two SQL statements in one:
(If "type" is "2")
SELECT *
FROM table1 t1
INNER JOIN table3 t3
ON t1.id = t3.t1_id
WHERE t1.pid = 100
(If "type" is NOT "2")
SELECT *
FROM table1 t1
INNER JOIN table2 t2
ON t1.id = t2.t1_id
INNER JOIN table3 t3
ON t2.id = t3.t2_id
WHERE t1.pid = 100
I'm guessing I could manage to do this with a UNION statement, but I'm confused on how to implement the WHERE t1.pid = '100' part.
use an UNION e.g.
SELECT t1.*, t3.*
FROM table1 t1
INNER JOIN table3 t3 ON t1.id = t3.t1_id
WHERE t1.pid = 100 and t1.type = 2
UNION
SELECT t1.*, t3.*
FROM table1 t1
INNER JOIN table2 t2
ON t1.id = t2.t1_id
INNER JOIN table3 t3 ON t2.id = t3.t2_id
WHERE t1.pid = 100 and t1.type <> 2;
but it would be better to explicitly name the columns you want to get back.
I have the following SQL query:
SELECT * FROM `table1` INNER JOIN `table2` ON table1.messageid=table2.messageid WHERE `venue_active` = 1
The above works fine but it only returns fields where both tables have a messageid field.
My problem is that I need it to return ALL fields from Table1 reguardless if it has a messageid match in table2 or not.
So, in other words I need ALL records to be returned from Table1 and all records from Table2 where there's a messageid that matches both.
How can I do this?
Use a LEFT JOIN rather
SELECT *
FROM `table1` LEFT JOIN
`table2` ON table1.messageid=table2.messageid
WHERE `venue_active` = 1
That said, it will only work if venue_active is also part of table1, and not table2.
Have a look at the different scenarios
SQL Fiddle DEMO
Use a LEFT join rather than INNER
For example:
SELECT * FROM `table1`
LEFT JOIN `table2` ON table1.messageid=table2.messageid
WHERE `venue_active` = 1
Either you need a LEFT JOIN instead, or
a FULL OUTER JOIN workaround for MySQL:
SELECT
a.*,
b.*
FROM
table1 a
LEFT JOIN
table2 b ON a.messageid = b.messageid
WHERE a.venue_active = 1
UNION
SELECT
a.*,
b.*
FROM
table1 a
RIGHT JOIN
table2 b ON a.messageid = b.messageid;
WHERE a.venue_active = 1
I am trying to get a query using fields from 2 tables.
I need to query Table1 but only Table2 has the variable venue_location that I need to query.
Basically I need to count all records on Table1 where Table1.venue_location = $MyVariable.
Here is what I've put together but I believe I need to use Joins for this?
Table1
- venue_id
Table2
- venue_id,
- venue_location
SELECT * FROM Table1 WHERE table1.venue_id = table2.venue_id and table2.location = '$MyVariable'
How can I do a query for this?
Use the power of join table
SELECT * FROM Table1
JOIN Table2 USING(venue_id)
WHERE table2.location = '$MyVariable'
You can get back the count of rows with mysqli_num_rows() in PHP, or change le select by SELECT COUNT(*) AS nbRow FROM ... and check of value in nbRow column
You can join two tables on venue_id and then group it by venue_id where location is your $MyVariable.
Your final query will look like:
SELECT count(table2.venue_id)
FROM Table1
JOIN Table2 ON table1.venue_id = table2.venue_id
WHERE table2.location = '$MyVariable'
GROUP BY table2.venue_id
try this
SELECT Table1.venue_id, Table2.venue_location FROM Table1 INNER JOIN Table2
ON Table1.venue_id='$MyVariable';
I can do the following in 2 queries but want to make it simpler. Can this be combined in one query? If so how more efficient is it than doing two queries vs one?
query1: SELECT page_id, coupon_id from table_1 WHERE key = :key
query2: SELECT folder from table_2 WHERE page_id = table_1.page_id
For my final result I need to have a coupon_id from table_1, and a folder from table_2.
In query2 I need to use the page_id result from query1 to get the folder
Is there a simpler way to do this?
Use JOIN (LEFT, RIGHT or INNER is up to your needs):
SELECT
t1.page_id,
t1.coupon_id,
t2.folder
FROM
table_1 AS t1
LEFT JOIN table_2 AS t2 ON
t2.page_id = t1.page_id
WHERE
t1.key = :key
You will want to JOIN the tables on the page_id:
SELECT t1.page_id,
t1.coupon_id,
t2.folder
from table_1 t1
inner join table_2 t2
on t1.page_id = t2.page_id
WHERE key = :key
If you need help learning join syntax, here is a great visual explanation of joins.
I used an INNER JOIN which will return all rows that match between the two tables. If you want to return all rows from table_1
even if it doesn't have a matching row in table_2, then you would use a LEFT JOIN
SELECT
table_1.coupon_id AS coupon_id,
table_2.folder AS folder
FROM
table_1
INNER JOIN table_2 ON table_2.page_id = table_1.page_id
WHERE
table_1.key = :key
SELECT t1.page_id, t1.coupon_id, t2.folder
FROM table_1 t1 LEFT JOIN table_2 t2 ON (t1.page_id = t2.page_id)
WHERE t1.key = :key
This will be faster than two queries, how much depends on your data.
Try this please:
SELECT a.page_id, a.coupon_id, b.folder_id
from table_1 a
join table_2 b
ON a.page_id = b.page_id
WHERE a.key = :key
group by a.page_id
;
I have two tables Table1 and Table2 with some records
id is the common column in both tables and primarykey is set to this column in table1
There are many records in table1 and some of these records (not all) are updated into table2.
Now I want retrieve from table1 the records not updated into the table2.
For example in table1 there are records 1,2,3,4,5,6,7,8,9
And in table2 there are 3,4,7,9
Now How can I retrieve these records form table1 1,2,5,6 those not updated into table2
I wrote this query :
SELECT Table1.id, Table1.DATE, Table1.C_NAME, Table1.B_NAME
FROM [Table1] INNER JOIN Table2 ON Table1.SLIPNO <>Table2.id;
But the expected result not coming. This query lists all the records repeating each one record manytimes
Can any body give me solution to get the expected result.
select *
from table1
where table1.slip_no NOT IN (select id from table2)
Assuming name of common column is id
Or you can modify your query as
SELECT distinct (Table1.id, Table1.DATE, Table1.C_NAME, Table1.B_NAME)
FROM [Table1]
INNER JOIN Table2 ON Table1.SLIPNO <>Table2.id
A good reference on SQL joins
SELECT t1.*
FROM table1 AS t1
LEFT OUTER JOIN table2 AS t2 USING(id)
WHERE
t2.id IS NULL;
You can use the NOT IN operator on a subquery for table2.
Alternatively, use MINUS with two regular queries listing the ids in each table:
SELECT id FROM table1
MINUS
SELECT id FROM table2;
Try this
SELECT Table1.id, Table1.DATE, Table1.C_NAME, Table1.B_NAME FROM [Table1]
WHERE
NOT EXISTS (SELECT * from Table2 WHERE Table1.SLIPNO !=Table2.id );
You can use the following query
SELECT id FROM database1.table WHERE id NOT IN(SELECT id FROM database2.table)
SELECT child_table.id FROM child_table LEFT JOIN parent_table ON child_table.parent_id = parent_table.id WHERE parent_table.id IS NULL
This left join query returns all the records of the child_table when there is no match in the parent_table. When there is no match, all parent_table fields will be NULL.
inner join will not help. To get unmatched records I tried this:
SELECT
A.ID,A.DATE,A.NAME
FROM TABLE1 A
WHERE CONCAT(A.ID , A.DATE ,A.NAME)
NOT IN
(SELECT CONCAT(B.ID , B.DATE ,B.NAME) as X
from TABLE2 B) ;