SQL join multiple tables with same column names into a new table?

Question

I have 12 tables where I need to combine 5 of the columns into a new table.

Each table is a different month but they all have the same column names.

I believe I need to use 11 join's, but when I use left join, I'm returning data only from the first table(jan). When I use full outer join I am returning rows full of Null's but looks like merged tables. I am using BigQuery.

SELECT 
  jan.ride_id, 
  jan.member_casual,
  jan.ride_length, 
  jan.day_of_week,
  jan.rideable_type
FROM 
  `jan_22` as jan 
  left join `feb_22` as feb 
  on jan.ride_id= feb.ride_id

The result I'm looking for is the 5 columns with data from all 12 tables merged. Just trying to merge the first 2 correctly before adding the others.

Also should I use select into or insert into for creating a new table with the 5 columns?

Thanks for your help.

Answer 1

As suggested by Mikhail Berlyant in the comments you should use union as the difference between join and union is that join joins a table horizontally and union joins vertically. And as you need 5 columns you should join them using union as follows:

insert dataset.new_table(<the columns(6)>)
SELECT 
  'Jan' as Month_Name,
  jan.ride_id, 
  jan.member_casual,
  jan.ride_length, 
  jan.day_of_week,
  jan.rideable_type
FROM 
  `jan_22` as jan 
UNION ALL
SELECT 
  'Feb',
  feb.ride_id, 
  feb.member_casual,
  feb.ride_length, 
  feb.day_of_week,
  feb.rideable_type
FROM `feb_22` as feb 
...

And as you probably have rows that return duplicate values it will be ignored by union but not by union all so you should use union all .

See here in docs how to insert into a table using select statement.