Is it possible to join the results of a SELECT with another table.
Like this:
SELECT * FROM table1 LEFT OUTER JOIN (SELECT * FROM table 2)
I know I need to link the column but am not sure how. Is this possible?
You need to know what columns you are joining on. Assuming they are called ID in both tables, something like this would work:
SELECT *
FROM table1 t1
LEFT OUTER JOIN (SELECT * FROM table 2) t2 on t1.ID = t2.ID
Note that rather than using *, you should name the columns you need explicitly. This will give a more efficient query if you do not need all of the data, and will also prevent duplicate column names from being returned.
You can do this. The code would be something like:
(SELECT id as leftid, [other fields] FROM table1) LEFT OUTER JOIN (SELECT id rightid, [other fields] FROM table2) ON (leftid=rightid)
I didn't test it, though...
Related
i would like to know if there is any shortcut to specify the column where IN have to check for matches.
Example:
Instead of this:
select *
from table1
where id in(
select column
from table2
)
something like this:
select *
from table1
where id in table2.column
I know the existence of TABLE for IN, ANY, SOME to specify a table, but it works only if the table specified is composed by just 1 column
EDIT: using join is not an option, because the real use i was looking for is on a NOT IN operator, and also JOIN create duplicates sometimes like in a one to many relation
There is no shortcut like that in SQL. Let me explain why.
In a query, all table references need to be made in the FROM clause. Hence, you cannot simply refer to table2.col unless table2 has been defined in the FROM clause. table2 is actually an alias, which defaults to the table name.
From a performance perspective, I would recommend exists:
select t1.*
from table1 t1
where exists (select column
from table2 t2
where t2.column = t1.id
)
In particular, this can take advantage of an index on table2(column) and has the same semantics as in.
Using a JOIN is a bit shorter. At least it does not require a subquery or another SELECT ... FROM.
SELECT table1.*
FROM table1
JOIN table2 ON table1.id = table2.column
Although this simple example is an inner join, not a semi-join. An inner join is different because it produces one row per matched row in table2. A semi-join only produces one row for each row in table1, even if it matches multiple rows in table2.
If you want to simulate a semi-join, use DISTINCT to reduce the result to one row per row of table1:
SELECT DISTINCT table1.*
FROM table1
JOIN table2 ON table1.id = table2.column
If you want to check for something like NOT EXISTS, use an exclusion join:
SELECT table1.*
FROM table1
LEFT OUTER JOIN table2 ON table1.id = table2.column
WHERE table2.column IS NULL
No need to use DISTINCT on the outer join example. There will be no row duplication from the join, because it can only "match no rows" once.
I have two table as table1 and table2 given below:
I want to have the value of only those table_name from table1 which has there id in print_table column in table 2.
I have implemented the following query but it returns only one value:
SELECT * FROM print_tabel_permission_admin WHERE id IN (select print_table from secondary)
Use FIND_IN_SET:
SELECT DISTINCT
t1.table_name
FROM table1 t1
INNER JOIN table2 t2
ON FIND_IN_SET(t1.id, t2.print_table) > 0;
Demo
You should probably move away from storing CSV data in your tables like this. Instead, break out the IDs in table2 onto separate rows. This will make your life easier.
I would like to select data from a table which looks like
ID|FOO|CITY|BAR
there is another table where all data which has been selected yet will be stored so that I get unique results. This table looks like
ID|ID_from_other_table
Now I'm stucking if I either should use a left join or a union?
Which one is faster and, how can I set this up the correct way?
left join would be probably faster in MySQL rather than other anti-join patterns like not in and not exists.
select t1.*
from table1 t1
left join table2 t2 on t1.id = t2.id_from_other_table
where t2.id is null
I have 2 tables in the same database.
I want to merge them based on the common id column. Because the tables are too huge I am not sure if there are duplicates.
How is it possible to merge these two tables into one based on the id and be sure that there are no duplicates?
SELECT *
FROM table1,table2
JOIN
GROUP BY id
What do you mean by merging two tables? Do you want records and columns from both the tables or columns from one and records from both?
Either way you will need to change the join clause only.
You could do a join on the columns you wish to
SELECT DISTINCT *
FROM table1 tb1
JOIN table2 tb2
ON table1.id = table2.id
Now if you want columns from only table1 do a LEFT JOIN
If you want columns from only table2 then a RIGHT JOIN
If you want columns from both the tables, use the query as is.
DISTINCT ensures that you get only a single row if there are multiple rows with the same data (but this distinct will check values for all columns in a row whether they are different or the same)
Union won't help if both tables have different number of columns. If you don't know about joins then use a Cartesian product
select distinct *
from table1 tb1, table2 tb2
where tb1.id = tb2.id
Where id is the column that is common between the tables.
Here if you want columns from only table1 do
select distinct tb1.*
Similarly replace tb1 by tb2 in the above statement if you just want table2 columns.
select distinct tb2.*
If you want cols from both just write '*'
In either cases I.e. joins and products said above if you need selective columns just write a table alias. E.g.
Consider :
table1 has id, foo, bar as columns
table2 has id, name,roll no, age
you want only id, foo, name from both the tables in the select query result
do this:
select distinct tb1.id, tb1.foo, tb2.name
from table1 tb1
join table2 tb2
on tb1.id=tb2.id
Same goes for the Cartesian product query. tb1, tb2 are BTW called as a table aliases.
If you want data from both the tables even if they have nothing in common just do
select distinct *
from table1 , table2
Note that this cannot be achieved using a join as join requires a common column to join 'on'
I am not sure What exactly do you want but anyway, this is your code
SELECT *
FROM table1,table2
JOIN
GROUP BY id
i just edit your query
SELECT *
FROM table1 JOIN table2
on table2.id = table1.id
GROUP BY table1.id // here you have to add table
//on which you will be group by at this moment this is table1
Try UNION:
https://dev.mysql.com/doc/refman/5.0/en/union.html
IT is very simple. Hope it will help.
Also you should have a look at "DISTINCT".
can u please show me how to query 3 tables using *? thanks
You need to do a join on the tables in order to get the columns of all of them.
Warning: using * to get all columns is bad practice. You should qualify (name) all the columns you need.
Here is an example:
SELECT *
FROM table1 t1
INNER JOIN table2 t2
ON t1.key2 = t2.key2
INNER JOIN table3 t3
ON t1.key3 = t3.key3
One way you probably don't like:
SELECT *
FROM table1, table2, table3
You have to give way more information.
This generates the Cartesian product of all the three tables.