See #pluck(*fields)

Select specifics columns and return an array of Tuple(*Clear::SQL::Any) containing the columns in the order of the selected arguments:

User.query.pluck("first_name", "last_name").each do |(first_name, last_name)|
  # ...
end

See #pluck_col(field)

Select a specific column of your SQL query, execute the query and return an array containing this field.

User.query.pluck_col("id") # [1,2,3,4...]

Note: It returns an array of Clear::SQL::Any. Therefore, you may want to use #pluck_col(str, Type) to return an array of Type:

User.query.pluck_col("id", Int64)

The field argument is a SQL fragment; it's not escaped (beware SQL injection) and allow call to functions and aggregate methods:

  # ...
  User.query.pluck_col("CASE WHEN id % 2 = 0 THEN id ELSE NULL END AS id").each do
  # ...