Interview Q&A / SQL & DBMS
SQL & DBMS interview questions
Joins, keys, normalisation, indexes and transactions for placement and backend interviews.
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- Write an SQL query to find the second highest salary.
Find the highest salary that is less than the maximum, with SELECT MAX(salary) FROM employees WHERE salary < (SELECT MAX(salary) FROM employees). For the Nth highest, use DENSE_RANK() so that duplicate salaries share a rank, or ORDER BY DISTINCT salary with LIMIT and OFFSET.
BeginnerIn-depthCoding3 min read - What happens when a subquery used with = returns more than one row?
The database raises an error such as "subquery returns more than 1 row", because = expects a single value. Use IN, ANY or ALL for multiple values, or make the subquery return one row with an aggregate or LIMIT.
BeginnerQuick answer1 min read - What is a derived table (subquery in FROM)?
A derived table is a subquery in the FROM clause that acts like a temporary table for that one statement. It must have an alias, and it is useful for filtering or aggregating before joining.
BeginnerQuick answer1 min read