How to keep in a database the number of calls of each record? - sql

Question

For example, I want to know at any moment most popular records that users searched in the database.
I expect that for each record I need to introduce a new number field. Thus, the record will be like this:
key - value - counter
How I can to increase the value of counter inside a database?
I think it's something like calling a stored procedure while a query, but I'm not sure. Perhaps the question is quite simple, I'm just a beginner and I apologize in that case.

Answer 1

You should use a trigger for this. Triggers are commands that execute on events, everytime an INSERT, UPDATE or DELETE statement is executed, even if their calls do not modify any records. Due tot this, you can't directly create a trigger for updating the count field of a record when you SELECT (read) it.
But, you can try a workaround in which you also have a date field in your table, and update it everytime a record is called. Use your application to send this datetime value to the database, which will trigger an UPDATE.
By making an UPDATE statement, your trigger is called and this way you can add your code to modify the count column.
CREATE TRIGGER tafter AFTER INSERT OR DELETE ON tbl1 FOR EACH ROW UPDATE SET counter = counter + 1 where key = 'keyval';

Answer 2

Firstly, this sounds like an awful performance problem. Every time you select a record you have to update it if you're tracking the selects with a single number, which just stores total selects, otherwise you have to insert timestamped values into another table to be able to analyse when the rows were read.
Anyway, you can do this with a common table expression in which you update a counter in the table and return the results to the main query: http://sqlfiddle.com/#!1/1aa41/6
Code something like:
create table my_table(col1 varchar(30), col2 numeric, select_count numeric);
insert into my_table values ('A',1,0);
insert into my_table values ('B',2,0);
insert into my_table values ('C',3,0);
insert into my_table values ('D',4,0);
insert into my_table values ('E',5,0);
with upd as (
update my_table
set select_count = select_count+1
where col1 = 'A'
returning *)
select *
from upd;
with upd as (
update my_table
set select_count = select_count+1
where col1 = 'B'
returning *)
select *
from upd;
with upd as (
update my_table
set select_count = select_count+1
where col1 = 'A'
returning *)
select *
from upd;
with upd as (
update my_table
set select_count = select_count+1
returning *)
select count(*)
from upd;
with upd as (
update my_table
set select_count = select_count+1
returning *)
select sum(col2)
from upd;
with upd as (
update my_table
set select_count = select_count+1
returning *)
select *
from upd;