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sql-note's Introduction

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
  • 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

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?

Resources

SQLZOO

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