Questions / Quant development, SQL & data pipelines
COUNT and NULL
A SQL table has four rows. Column x contains 7, NULL, 9, NULL. What does COUNT(x) return?
Answer it in the app It's free. You get hints, a second try if you miss, and a follow-up question.
Show the answer and worked solution
Answer: 2 count
- COUNT(x) counts non-null values of x, so it returns 2.
Interview shortcut. COUNT(col) skips NULLs.
In the app this has a follow-up where one thing about the setup changes. Try the follow-up.