How to update a field by adding a value to the existing value?

[eluser]toopay[/eluser]

Code:

+-----------------+
| players_table   |
+-----------------+
| id              |
| name            |
| team_id         |
+-----------------+

+-----------------+
| goals_table     |
+-----------------+
| id              |
| minutes         |
| player_id       |
| home_team_id    |
| away_team_id    |
| match_date      |
+-----------------+