I need to optimize my MariaDB tables index. I’ve read a lot of very interesting things on StackExchange, but I’m not sure to have the answer for my case.

In my case, I have a table named TableA which contains more than 40 millions records (stats purposes) with these columns :

• ID (PK)
• A (INT)
• B (INT)
• C (INT)
• D (INT)

I make different queries on this table, with many of the 4 columns in the WHERE clause. For example, I can have these columns in WHERE clause of the same query :

• A, B and C
• A and B
• A and D
• A, C and D
• B and D
• B, C and D
• C and D
• only A
• only B
• etc.

I can encounter every case. What would be the best way to index that table which count more than 40 millions records ? Should I make only one INDEX with all 4 columns ? Or 4 different indexes ? This table is used everytime in my app, and contains sensitive data…(for stats purposes).

Thank you for your help !

Joffrey