SQL practice note
Important Concepts
-
Nested Queries
- Nested Query Results Expressions
- ALL: Must satisfy expression for all rows in subquery
- ANY: Must satisfy expression for at least one row in subquery
- IN: Equivalent to "=ANY()"
- EXISTS: At lease one row is returned
- Nested Query Results Expressions
-
Window Functions
- Perform a calculation across a set of tuples that related to a single row
- SELECT ... FUNC-NAME(...) OVER(...) FROM TableName
- Functions:
- Aggregate Functions
- Special Windown Functions:
- ROW_NUMBER()
- RANK()
- Grouping: The OVER clause specifies how to group together tuples when computing the window function Use PARTITION BY to specify group
-
Common Table Expressions (CTE)
- Think of it like a temp table for one query
- Alternative to nested queries and views
- Bind output columns to names before the AS keyword
- A single query can contain multiple CTE declarations
Practice
Leetcode
- 184. Department Highest Salary
- 185. Department Top Three Salaries
- 262. Trips and Users
- 595. Big Countries
- 569. Median Employee Salary
- without built-in SQL functions?
- 601. Human Traffic of Stadium
Common Interview Questions
- What are the different types of SQL commands? Explain the DDL/DCL commands in SQL?
- What is the difference between Cluster and Non-Cluster Index?
- the use of UNION and UNION ALL in SQL?
- What is the difference between DELETE and TRUNCATE?
- What is a join? types of Join?
- How to test for NULL values?
- What is Normalization? What are all the different Normalization?