TheDataScientist

Practice track

SQL

Joins, window functions, aggregation and the queries interviews actually ask for.

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  1. 01

    Second highest salary per department

    Return the second highest salary in each department. If a department has fewer than two distinct salaries, it should not appear. Handle…

    SQL problemINTERMEDIATEDifficulty: INTERMEDIATEWindow functions~8 min
  2. 02

    Running total that resets each month

    Produce a running total of amount per customer that resets at the start of each calendar month, ordered by transaction date.

    SQL problemINTERMEDIATEDifficulty: INTERMEDIATEWindow functions~7 min
  3. 03

    What happens to row counts in a LEFT JOIN?

    Table orders has 1,000 rows. Table orderitems has 3,500 rows, with every item belonging to an order, and 50 orders have no items at all.…

    Multiple choiceBEGINNERDifficulty: BEGINNERJoins~3 min