Week 9-10: SQL & Database Keys

Introduction about Key

A Key is a data item that exclusively identifies a record. In other words, key is a set of column(s) that is used to uniquely identify the record in a table. It is used to fetch or retrieve records / data-rows from data table according to the condition/requirement. Key provide several types of constraints like column can’t store duplicate values or null values. Keys are also used to generate relationship among different database tables or views.

Types of Keys

Database supports the following types of keys.

  • Super Key
  • Minimal Super Key
  • Candidate Key
  • Primary Key
  • Unique Key
  • Alternate Key
  • Composite Key
  • Foreign Key
  • Natural Key
  • Surrogate Key

What is SQL?

  • SQL stands for Structured Query Language
  • SQL lets you access and manipulate databases
  • SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987

What Can SQL do?

  • SQL can execute queries against a database
  • SQL can retrieve data from a database
  • SQL can insert records in a database
  • SQL can update records in a database
  • SQL can delete records from a database
  • SQL can create new databases
  • SQL can create new tables in a database
  • SQL can create stored procedures in a database
  • SQL can create views in a database
  • SQL can set permissions on tables, procedures, and views

 

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