I have the following data structure :
FIRSTNAME AGE NICKNAME
Jack 28 Benny
Robert 30 Benny
Pascal 20 Benny
Charles 19 Lence
Anthony 20 Lence
The first column is unique.
The idea is that I have to count how many times the "nickname" is used and I want to output it so that I can I have the following result :
Benny 3
Lence 2
What is the best performant way to do so knowing that I have millions of lines?
Try this:
SELECT NICKNAME,COUNT(NICKNAME)
FROM MyTable
GROUP BY NICKNAME
SELECT NICKNAME, SUM(1) FROM table GROUP BY NICKNAME
agregate count group by firstname, there's no other solution.
by the way, the benny nickname only appears 3 times, not 4.
Related
MY SQL returns the following array...
id
staff
province
1
Ben
Ontario
2
Ben
Quebec
3
John
Manitoba
4
John
Saskatchewan
6
Kitty
Alberta
7
Kitty
Nova Scotia
I would like to have the record displayed like this...
staff
province
Ben
Ontario, Quebec
John
Quebec, Manitoba, Saskatchewan
Kitty
Alberta, Nova Scotia
what approach should I use to approach this?
Would be better to post the tables as well for clearer context.
You can use Aggregate functions and Grouping to help doing this. A GROUP BY to group the rows by staff column, then use GROUP_CONCAT() to concatenate province values in one string.
A reference of how you want it to be, unsure what table you are using or if there are any other factors but you can adapt as needed.
SELECT staff, GROUP_CONCAT(province SEPARATOR ', ') as province
FROM table_name
GROUP BY staff;
name | course
Jay | LAWS0001
Mark | LAWS0002
Sam | LAWS0002
Alice | LAWS0001
Ryan | LAWS0001
Ryan | LAWS0002
Hey guys, I've got this database and I want to only select the names that take both 'LAWS0001' and 'LAWS0002'. So from this example, it should select 'Ryan' because he's the only person to take both courses.
I tried IN operator:
SELECT name
FROM student
WHERE course IN ('LAWS0001', 'LAWS0002')
but this takes everyone because everyone is taking either of the courses.
Is there an operator for my problem?
You can use your existing query, using a GROUP BY clause to COUNT the number of distinct courses each student is taking in the set ('LAWS0001', 'LAWS0002') and only selecting those students where the count is 2:
SELECT name
FROM student
WHERE course IN ('LAWS0001', 'LAWS0002')
GROUP BY name
HAVING COUNT(DISTINCT course) = 2
Demo on SQLFiddle
Not sure how to describe this, but I want to group a row of values, where one field has two or more different values and set the value of that (but concatenating or changing the values) to give just one single row.
For example:
I have a simple table (all fields are Strings) of people next to their departments. But some people belong to more than one department.
select department_ind, name
from jobs
;
department_ind name
1 Michael
2 Michael
2 Sarah
3 Dave
2 Sally
4 Sally
I want to group by name, and concatenate the department_ind. So the results show look like:
department_ind name
1,2 Michael
2 Sarah
3 Dave
2,4 Sally
Thanks
Use string_agg()
select string_agg(department_ind::text, ',') as departments,
name
from jobs
group by name;
Due to the way a particular table is written I need to do something a little strange in SQL and I can't find a 'simple' way to do this
Table
Name Place Amount
Chris Scotland
Chris £1
Amy England
Amy £5
Output
Chris Scotland £1
Amy England £5
What I am trying to do is above, so the null rows are essentially ignored and 'grouped' up based on the Name
I have this working using For XML however it is incredibly slow, is there a smarter way to do this?
This is where MAX would work
select
Name
,Place = Max(Place)
,Amount = Max(Amount)
from
YourTable
group by
Name
Naturally, if you have more than one occurance of a place for a given name, you may get unexpected results.
I have a table similar to the below:
id | name | direction |
--------------------------------------
1 Jhon Washington, DC
2 Diego Miami, Florida
3 Michael Orlando, Florida
4 Jenny Olympia, washington
5 Joe Austin, Texas
6 Barack Denver, Colorado
and I want to count how many people live in a specific state:
Washington 2
Florida 2
Texas 1
Colorado 1
How can I do this? (By the way this is just an question with an academic point of view )
Thanks in advance!
Postgres offers the function split_part(), which will break up a string by a delimiter. You want the second part (the part after the comma):
select split_part(direction, ', ', 2) as state, count(*)
from t
group by split_part(direction, ', ', 2);
Initially I would obtain the state from the direction field. Once you have that, it's quite simple:
SELECT state, count(*) as total FROM initial_table group by state.
To obtain the state, some functions depending on the dbms are useful. It depends on the language.
A possible pseudocode (given a function like substring_index of MySQL) for the query would be:
SELECT substring_index(direction,',',-1) as state, count(*) as total
FROM initial_table group by substring_index(direction,',',-1)
Edit: As it is suggested above, the query should return 1 for the Washington state.
My way do making such a queries is two-step - first, prepare fields you need, second, do you grouping or other calculation. That way you're following DRY principle and don't repeating yourself. I think CTE is the best tool for this:
with cte as (
-- we don't need other fields, only state
select
split_part(direction, ', ', 2) as state
from table1
)
select state, count(*)
from cte
group by state
sql fiddle demo
If you writing queries that way, it's easy to change grouping field in the future.
Hope that helps, and remember - readability counts! :)