text: -- 1.Arithematics
  select price * billing_frequency as revenue from memberships;
  
  -- 2. Functions
  -- CEIL, FLOOR, ROUND, TRUNC or TRUNCATE (just cuts off the decimal places no matter what the value is)
  select consumption from memberships;
  
  -- 3. Concat
  select concat(first_name, ' ', last_name) as Name from memberships;
  select concat('$ ', price) as Price from memberships;
  
  -- 4. Upper / lower case
  select upper('Maran');
  select lower('Maran');
  
  -- 5. Finding length
  select length('Maran');
  
  -- 6. Trimming a string
  select trim('    Maran     ');
  select trim(leading ' ' from  '    Maran     ');
  
  -- 7. Extracting month, day, day of the week from date
  select extract(day from last_checkin), last_checkin from memberships;
  select extract(month from last_checkin), last_checkin from memberships;
  -- For Postgres
  select extract(dow from last_checkin), last_checkin from memberships;
  -- For MySQL
  select weekday(last_checkin) from memberships;
  
  -- 8. Convert time stamps into date or time
  -- For MySQL
  select convert(last_checkin, date), convert(last_checkin, time) from memberships;
  -- For Postgres
  select last_checkin::TIMESTAMP::DATE, last_checkin::TIMESTAMP::TIME from memberships;
  
  -- 9. Finding difference between two timestamps
  -- For MySQL
  select TIMESTAMPDIFF(MINUTE, last_checkin, last_checkout) from memberships;
  -- For Postgres
  select last_checkin - last_checkout from memberships;
  
  -- 10. Finding difference between two dates
  -- For MySQL
  select DATEDIFF(membership_end, membership_start) from memberships;
  -- For Postgres
  select membership_start - membership_end from memberships;
  
  -- 11. Adding days to an existing date
  -- For MySQL
  select DATEADD(membership_start, INTERVAL 7 DAY) from memberships;
  -- For Postgres
  select membership_start + INTERVAL '7 DAY' from memberships;
  
  