sql - Row Rank in a MySQL View

Question

I need to create a view that automatically adds virtual row number in the result. the graph here is totally random all that I want to achieve is the last column to be created dynamically.

> +--------+------------+-----+
> | id     | variety    | num |
> +--------+------------+-----+
> | 234    | fuji       |   1 |
> | 4356   | gala       |   2 |
> | 343245 | limbertwig |   3 |
> | 224    | bing       |   4 |
> | 4545   | chelan     |   5 |
> | 3455   | navel      |   6 |
> | 4534345| valencia   |   7 |
> | 3451   | bartlett   |   8 |
> | 3452   | bradford   |   9 |
> +--------+------------+-----+

Query:

SELECT id, 
       variety, 
       SOMEFUNCTIONTHATWOULDGENERATETHIS() AS num 
  FROM mytable

Answer 1

Use:

SELECT t.id,
       t.variety,
       (SELECT COUNT(*) FROM TABLE WHERE id < t.id) +1 AS NUM
  FROM TABLE t

It's not an ideal manner of doing this, because the query for the num value will execute for every row returned. A better idea would be to create a NUMBERS table, with a single column containing a number starting at one that increments to an outrageously large number, and then join & reference the NUMBERS table in a manner similar to the variable example that follows.

MySQL Ranking, or Lack Thereof

You can define a variable in order to get psuedo row number functionality, because MySQL doesn't have any ranking functions:

SELECT t.id,
       t.variety,
       @rownum := @rownum + 1 AS num
  FROM TABLE t,
       (SELECT @rownum := 0) r

• The SELECT @rownum := 0 defines the variable, and sets it to zero.
• The r is a subquery/table alias, because you'll get an error in MySQL if you don't define an alias for a subquery, even if you don't use it.

Can't Use A Variable in a MySQL View

If you do, you'll get the 1351 error, because you can't use a variable in a view due to design. The bug/feature behavior is documented here.