im looking for a simple logic to merge two tables and expected result is given below.
is it possible to achieve it using SQL join or concatenate commands?
how can i achieve it?
here is the logic I'm working on and trying to find solution:
TABLE 1:
ID Name Title Age
2 Paul Technical Support 22
4 Janne IT Specialist 27
1 Wladimir Team Lead 31
3 Mark Customer Support 40
TABLE 2:
ID Name Title Age
2 Paul Technical Support 22
4 Janne IT Specialist
1 Wladimir 31
3 Mark Customer Support 40
Expected result after merge:
ID Name Title Age
2 Paul Technical Support 22
4 Janne IT Specialist 27
1 Wladimir Team Lead 31
3 Mark Customer Support 40
You should use the following query for this
select t1.id,t1.name,t1.title,t1.age,t2.id,t2.name.t2.title,t2.age from table1 t1 join table2 t2 where t1.id=t2.id
Related
I want to join two tables and use the column they both share to group the results, including a null result for those accountIds which only appear in one table.
Table a
AccountId
productApurchases
Steve
1
Jane
5
Bill
10
Abed
2
Table b
AccountId
productApurchases
Allan
1
Jane
10
Bill
2
Abed
1
Mike
2
Desired output
AccountId
productApurchases
productBpurchases
Steve
1
0
Jane
5
10
Bill
10
2
Abed
2
1
Mike
0
2
I've been trying with various joins but cannot figure out how to group by all the account ids.
Any advice much appreciated, thanks.
Use full join:
select accountid,
coalesce(productApurchases, 0) as productApurchases,
coalesce(productBpurchases, 0) as productBpurchases
from a full join
b
using (accountid);
I'm seriously struggling with some easy stuff.
Currently I have 2 tables (tmp_jmo and persons)
table tmp_jmo
----------
ID ADRESS PERSON_ID
115 Street 1 (null)
120 Street 2 (null)
121 Street 3 (null)
Table persons
ID NAME PERSON_ID
----------
115 John 14
120 Ellen 27
121 Mark 114
Now I want to update the Peson_id from tmp_jmo with the values from person_id (persons table)
In this case I've getting the error that there are to many values
Update tmp_jmo t SET person_id = persons.person_id where tmp_jmo.id = persons.id;
I've also tried to with temporary data but also failing.
I'm sorry to interrupt you with this kind of questions but it's ruining my day!
Many thanks!
In Standard SQL, you can do:
update tmp_jmo t
set person_id = (select p.person_id from persons p where tmp_jmo.id = p.id);
Many databases also support join or from in updates, but that is database-specific syntax.
Question brief
I'm doing this practice on w3resource and I couldn't understand why the solution worked. I'm 2 days old to SQL. I'll appreciate very much if someone can help me explain.
I have 2 tables, COMPANY(com_id, com_name) and PRODUCT(pro_name, pro_price, com_id). Each company has several products with different prices. Now I need to write a query to display companies' name together with their most expensive products respectively.
The sample answer on the practice is like this
SELECT c.com_name, p.pro_name, p.pro_price
FROM product p
INNER JOIN company c ON p.com_id = c.com_id
AND p.pro_price =
( SELECT MAX(p.pro_price)
FROM product p
WHERE p.com_id = c.com_id );
The query returned expected result.
com_name pro_name pro_price
--------- --------- -----------
Samsung Monitor 5000.00
iBall DVD drive 900.00
Epsion Printer 2600.00
Zebronics ZIP drive 250.00
Asus Mother Board 3200.00
Frontech Speaker 550.00
But I cannot understand how, especially the part inside the bottom sub-query. Isn't SELECT MAX(p.pro_price) supposed to return only 1 highest price of all companies together?
I also tried subsecting this sub-query like this
SELECT MAX(p.pro_price)
FROM product p
INNER JOIN company c ON p.com_id = c.com_id
WHERE p.com_id = c.com_id;
... and it only returned 1 maximum value.
max(p.pro_price)
-----
5000.00
So how does the final result of the whole query include more than 1 records? There's no GROUP BY or anything.
By the way, the query seemed to use 2 conditions for INNER JOIN. But I also tried swapping the 2nd condition into a WHERE clause and it still worked the same. This is one more thing I don't understand.
The databases involved
COMPANY table
COM_ID | COM_NAME
----------------
11 | Samsung
12 | iBall
13 | Epsion
14 | Zebronics
15 | Asus
16 | Frontech
PRODUCT table
PRO_NAME PRO_PRICE COM_ID
-------------------- ---------- ---------
Mother Board 3200 15
Key Board 450 16
ZIP drive 250 14
Speaker 550 16
Monitor 5000 11
DVD drive 900 12
CD drive 800 12
Printer 2600 13
Refill cartridge 350 13
Mouse 250 12
The sub-query is a correlated sub-query. This query is executed for each value of c.com_id in the outer query:
WHERE p.com_id = c.com_id
Consider the following Postgresql database table:
id | book_id | author_id
---------------------------
1 | 1 | 1
2 | 2 | 1
3 | 3 | 2
4 | 4 | 2
5 | 5 | 2
6 | 6 | 3
7 | 7 | 2
In this example, Author 1 has written 2 books, Author 2 has written 4 books, and Author 3 has written 1 book. How would I determine the average number of books written by an author using SQL? In other words, I'm trying to get, "An author has written an average of 2.3 books".
Thus far, attempts with AVG and COUNT have failed me. Any thoughts?
select avg(totalbooks) from
(select count(1) totalbooks from books group by author_id) bookcount
I think your example data actually only has 3 books for author id 2, so this would not return 2.3
http://sqlfiddle.com/#!15/3e36e/1
With the 4th book:
http://sqlfiddle.com/#!15/67eac/1
You'll need a subquery. The inner query will count the books with GROUP BY author; the outer query will scan the results of the inner query and avg them.
You can use a subquery in the FROM clause for this, or you can use a CTE (WITH expression).
For an average number of books per author you can do simply:
SELECT 1.0*COUNT(DISTINCT book_id)/count(DISTINCT author_id) FROM tbl;
For number of books per author:
SELECT 1.0*COUNT(DISTINCT book_id)/count(DISTINCT author_id)
FROM tbl GROUP BY author_id;
We need 1.0 factor to make the result not integer.
You can remove DISTINCT depending of result you want (it matters only if one book have many authors).
As Craig Ringer rightly pointed out 2 distincts may be expensive. For test performance I have generated 50 000 rows and I got followng results:
My query with 2 DISTINCTS: ~70ms
My query with 1 DISTINCT: ~40ms
Martin Booth's approach: ~30ms
Then added 1 milion rows and tested again:
My query with 2 DISTINCTS: ~1520ms
My query with 1 DISTINCT: ~820ms
Martin Booth's approach: ~1060ms
Then added another 9 milion rows and tested again:
My query with 2 DISTINCTS: ~17s
My query with 1 DISTINCT: ~11s
Martin Booth's approach: ~19s
So there is no universal solution.
This should work:
SELECT AVG(cnt) FROM (
SELECT COUNT(*) cnt FROM t
GROUP BY author_id
) s
Assume I have a table with the following data:
Name TransID Cost
---------------------------------------
Susan 1 10
Johnny 2 10
Johnny 3 9
Dave 4 10
I want to find a way to sum the Costs per name (assume the Names are unique) so that I get a table like this:
Name Cost
---------------------------------------
Susan 10
Johnny 19
Dave 10
Any help is appreciated.
This is relatively straightforward: you need to use a GROUP BY clause in your query:
SELECT Name,SUM(Cost)
FROM MyTable
GROUP BY Name