Question

I have a table with several hundred records, each one containing a datetime column. What is the most efficient way to find the distinct years from that datetime field?

Answer 1

Using Ruby (this would require loading all the records, though):

Model.select("my_datetime").map{ |item| item.my_datetime.year }.uniq

Using SQL (this example is for PostgreSQL, I can update it with your specific database):

# PostgreSQL
Model.select("distinct(extract(year from my_datetime))")

# MySQL
Model.select("distinct(year(my_datetime))")

# SQLite
Model.select("strftime('%Y', my_datetime)")