How to add a user defined column with a single value to a SQL query

Question

I currently have a SQL query that produces a table with around 10M rows. I would like to append this table with another column that has the same entry for all 10M rows.

As an example consider the following toy query

SELECT PRODUCT_ID, ORDER_QUANTITY
FROM PRODUCT_TABLE
GROUP BY SALES_DAY

And say that is produces the following table

 PRODUCT_ID ORDER_QUANTITY`     
      1          10
      2          12
      3          14

How can I change this query so that it produces the following table, where every entry in USER_VALUE is 999.

 PRODUCT_ID ORDER_QUANTITY USER_VALUE  
      1           10         999
      2           12         999
      3           14         999

I realize that there may be several answers here... but I suppose that it would help to know the method that would be produce the table with the smallest file size (I assume this would require specifying the type of data beforehand).

Answer 1

Like this:

SELECT PRODUCT_ID, ORDER_QUANTITY, 999 as USER_VALUE FROM PRODUCT_TABLE GROUP BY SALES_DAY 

Answer 2

You can pass it in the SELECT, for example:

SELECT PRODUCT_ID, ORDER_QUANTITY, 999 AS USER_VALUE FROM PRODUCT_TABLE GROUP BY SALES_DAY 

Answer 3

you can use

SELECT PRODUCT_ID, ORDER_QUANTITY, user_value=999
    FROM PRODUCT_TABLE
    GROUP BY SALES_DAY