SELECT
Players.player_id,
Players.player_name,
SUM(Players.player_id = Championships.Wimbledon) + SUM(Players.player_id = Championships.Fr_open) + SUM(Players.player_id = Championships.US_open) + SUM(Players.player_id = Championships.Au_open) AS grand_slams_count
FROM Players
INNER JOIN Championships
ON (
Players.player_id IN (
Championships.Wimbledon,
Championships.Fr_open,
Championships.US_open,
Championships.Au_open
)
)
GROUP BY 1;