Quick SQL Notes for Beginners

In this post, we’ll cover some quick notes on SQL, including relational and non-relational databases, and various SQL queries and operators.

Relational Database: A database structured to recognize relations among stored items of information.

Non-Relational Database: A database that does not use a tabular schema of rows and columns.

SQL: A domain-specific language used in programming and designed for managing data in relational databases. It was initially developed by IBM.

Retrieving Data from a Single Table:

  • Use SELECT DISTINCT to retrieve unique items.
  • Mathematical operators can be used in the SELECT clause.
  • Use WHERE clause with AND, OR, and NOT operators.
  • IN operator: SELECT * FROM Customers WHERE state IN ('VA', 'FL', 'GA')
  • BETWEEN operator: selects values within a given range (inclusive).
  • LIKE operator: pattern matching with % and _.
  • REGEXP: pattern matching with regular expressions.
  • IS NULL: to filter records with null values.
  • ORDER BY: to sort records by a specified column.
  • LIMIT: to limit the number of records returned.

Retrieving Data from Multiple Tables:

  • INNER JOIN: combines records from two or more tables.
  • SELF JOIN: joins a table to itself.
  • Joining multiple tables with compound join conditions.
  • Implicit join syntax: SELECT * FROM orders o, customers c WHERE o.customer_id = c.customer_id
  • OUTER JOIN: two types – LEFT JOIN and RIGHT JOIN.
  • SELF OUTER JOIN: an outer join involving a table with itself.
  • USING: to specify columns for comparison in a join.
  • NATURAL JOIN: to join two tables based on columns with the same name and compatible data types.
  • UNION: combines the results of two or more queries.

These quick notes should help you get started with SQL and provide a basic understanding of how to write and execute SQL queries. As you gain experience, you’ll be able to explore more advanced features and techniques to manage your data effectively.

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