Question

I have a table that looks like this:

table name: uno
str_id | title
----------
 "a1"  | "hi"
 "b2"  | "bye"
 "c3"  | "etc."

table name: dos
str_id | other_col_name
-------------------------
   "b2"  |  1
   "b2"  |  5
   "a1"  |  6
   "b2"  |  7

I would like my query to look at the values in uno.str_id and then figure out an ordering of str_ids that have the most values in dos.str_id. I think I will need to join them on str_id and then order by count, but I am unsure how to do this in SQL syntax. Thanks for your time and help.

Answer 1

SELECT u.str_id FROM uno u
INNER JOIN dos d ON d.str_id = u.str_id
GROUP BY u.str_id
ORDER BY COUNT(*) DESC;

EDIT

the possible WHERE part must be put after the JOIN part (SQL syntax).

You MUST use aliases (or complete table name) if you’re querying on two tables with “same-named” fields, if you do anything with these common fields. In that query, Table uno is aliased as “u” and table dos is aliased as “d”. This mean, if you have a field title in uno and in dos, you have to write u.title to query on uno.title

version with aliases :

SELECT u.str_id FROM uno u
INNER JOIN dos d ON d.str_id = u.str_id
GROUP BY u.str_id
WHERE u.title = 'bla blabla'
AND d.title IN ('asdf', 'ersg')
ORDER BY COUNT(*) DESC;

version without aliases (complete table name to avoid confusion for DBMS)

SELECT uno.str_id FROM uno 
INNER JOIN dos  ON dos.str_id = unon.str_id
GROUP BY uno.str_id
WHERE uno.title = 'bla bla bla'
AND dos.title IN ('asdf', 'ersg')
ORDER BY COUNT(*) DESC;