Refresher/SQL

This is a refresher course for those who need to review basic knowledge of SQL.

For a comprehensive tutorial, go to http://www.1keydata.com/sql/sql.html.

Basic Concepts

 * Constraint: an input filter
 * Denormalizing: performance improvement through reduction in number of joins needed for data processing
 * Group by and order by clauses: expensive due to creation of temporary tables
 * Indexes' tradeoffs: faster retrieval, slower updates
 * Join: a logical connection between two tables
 * Normalizing: eliminating redundant information and making it easier for future updates
 * Primary key: a combination of columns which uniquely specify a row
 * Trigger: the code automatically executed in response to certain table events
 * Where vs having: where is a restriction and having is a filter
 * Wildcard: % using LIKE

Most Frequently Asked

 * Inner join: intersection, e.g. SELECT Person.LastName, Person.FirstName, Sales.OrderNo FROM Person INNER JOIN Sales ON Person.P_Id=Sales.P_Id ORDER BY Person.LastName
 * Outer join: union, e.g.
 * Foreign key: primary key of another table.

Comprehensive Tutorial
For a comprehensive tutorial, go to http://www.1keydata.com/sql/sql.html.