Create a view with column num_rows - MySQL
I found a solution for this:
First create a function:
delimiter //
CREATE FUNCTION `func_inc_var_session`() RETURNS int
NO SQL
NOT DETERMINISTIC
begin
SET @var := @var + 1;
return @var;
end
//
delimiter ;
Then set @var to the number you want to start with. In this case zero.
SET @var=0;
Then create the view as following:
CREATE OR REPLACE VIEW myview (place, name, hour, price, counter)
AS SELECT place, name, hour, price, func_inc_var_session()
FROM yourtable
WHERE input_conditions_here;
The trick here is that you may see NULL on the counter column. If this happens please set @var again to your number and then do the SELECT * again and you'll see the counter column properly populated.
I tried the example of the func_inc_var_session
function.
There was a small problem of session variable initialization that I solved using the mysql IFNULL
function.
Below the enhanced func_inc_var_session
function.
CREATE DEFINER=`root`@`localhost` FUNCTION `func_inc_var_session`() RETURNS int(11)
begin
SET @var := IFNULL(@var,0) + 1;
return @var;
end
When using the solution from @dazito you might encounter an issue with the counter continually incrementing from query to query, for example when your application reuses a session, like with JPA / Hibernate. For example:
Query 1:
| country | name | price | row_num | ------------------------------------ | US | john | 20 | 1 | | France | Anne | 10 | 2 | | Sweden | Alex | 5 | 3 |
Query 2:
| country | name | price | row_num | ------------------------------------ | US | john | 20 | 4 | | France | Anne | 10 | 5 | | Sweden | Alex | 5 | 6 |
etc.
One solution to this is to join the main query with a (one-time) call to the counter function and parameterize the function (the 'reset' parameter below) to let it know it is the first call.
delimiter // CREATE FUNCTION `func_inc_var_session`(reset BIT) RETURNS int NO SQL NOT DETERMINISTIC begin IF reset THEN SET @var := 0; ELSE SET @var := IFNULL(@var,0) + 1; END IF; return @var; end // delimiter ;
Now you can call the function in your view query with the reset parameter set to 1 to set the function's counter variable back to 0, and with 0 to increment the counter. The function will only get called once with 1 as a parameter when joining with it as below:
CREATE OR REPLACE VIEW country_view (country, name, price, row_num) AS SELECT country, name, price, func_inc_var_session(0) FROM country JOIN (SELECT func_inc_var_session(1)) r
Now you are guaranteed row number 1, 2, 3 every time.