Index first N characters of column

Question

I don't have much experience with SQL databases and MariaDB, but for my understanding of how indexes work, I think there should be a way to index the first N characters of a SQL column.

Take as example the following strings in a column:

123abc
123def
123ghi
234fhg
234kgf
567kds
567ops

If I index just the first 3 characters, which are repetitive, I could get some performance gain during the SELECT operations because it would be split in 3 big blocks (123, 234, 567).

Is it possible? Or I'd have to add a second column with just the first 3 characters of each row and index it?

Answer 1

Yes, it is possible. Assuming your table name is tmp and the column you want to index is col, this would be the way to create an index on the first 3 characters of the column:

alter table tmp add index first3Characters (col(3));

See also: MySQL Index on first part of string