SQL.md

1. What happens when you select count(name) from persons table ?

   --> It will return the number of rows where name is not null

2. What is CASE and how to use it ?

SELECT player_name,
       height,
       CASE WHEN height > 74 THEN 'over 74'
            WHEN height > 72 AND height <= 74 THEN '73-74'
            WHEN height > 70 AND height <= 72 THEN '71-72'
            ELSE 'under 70' END AS height_group
  FROM benn.college_football_players

3. How to concatenate two columns in bigquery and add word between. For example column name is "Marry" and column gender is "F". New column should be "Marry is a girl"

SELECT CONCAT(name, ' is ', case when gender = 'F' then 'girl' else 'boy' end) as intro FROM `baby_names`