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Sql Overview




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  • 04/08/10 CIS-182 SQL

Sql Overview Sql Overview Presentation Transcript

  • SQL Overview CIS-182
  • Structured Query Language
    • Language used to work with databases
    • Used in ‘back end’
      • Typically not part of user interface (don’t expect users to type in a query…)
  • SEQEL to SQL
    • Structured English Query Language developed by IBM
    • Other companies developed similar products
    • ANSI set standards in 1986
      • Standards are ‘open’
      • Different vendors have different levels of conformance
  • SQL
    • Most languages are procedural
      • Describe how to perform a task
    • SQL is non-procedural (declarative)
      • Code describes results
      • Includes some procedural components
        • If … Then, Loops
    • Database apps typically use both types of languages
      • Procedural languages manage interface, data requests
      • SQL manages data storage and retrieval
  • Types of SQL Statements
    • Data Definition Language (DDL): Create/edit objects
    • Data Control Language (DCL): Specify access and permissions
    • Data Manipulation Language (DML): Work with data
      • SELECT * FROM Employees
      • INSERT INTO Students
  • Logical Organization
    • Catalogs: group of schemas
    • Schema: group of related tables, views
    • Implementation is up to vendor
      • Some vendors use catalogs, some don’t
      • Vendors have different levels of support for schemas
  • Databases
    • ‘ Database’ is not an ANSI specification
    • Most vendors have a database object
    • In practice, schema and database tend to be viewed interchangeably
      • Schema defines the contents of a database
      • May have sub-schemas to reflect application needs (include only a portion of the database)
  • Coding
    • One command may extend across several lines
      • [Enter] doesn’t represent the end of a statement
      • SQL uses ; (semi-colon) to identify statement end
        • ; is optional in SQL Server
    • Keywords are capitalized
      • CREATE DATABASE MyNewDatabase
    • No standard conventions for naming
      • Typically use Pascal case naming with each new word capitalized
  • Naming Requirements
    • Object names are not typically case sensitive
      • Delimited identifiers wrap names in double quotes and ARE case sensitive
      • “ MyNewTable” uses double quotes to identify the object name
      • Single quotes identify strings (text)
    • Can use letters, numbers, underscore
      • Can’t use spaces, punctuation
  • Qualified Names
    • A qualified name defines explicitly how to find an object
      • ‘ .’ is used as separator
    • SQL Server uses ServerName.DatabaseName.OwnerName.ObjectName
    • OR
    • ServerName.DatabaseName.SchemaName.ObjectName
  • Coding Reference
    • SQL Server uses special characters to identify different parts of commands
    • End of statement: ;
      • Optional in SQL Server
    • Placeholder: <>
    • Placeholder Definition: ::=
    • Optional Parameter(s): [ ]
    • Specific Parameter Values: { }
    • Value Separator: |
    • List Separator: ,
  • Placeholder Example
    • Basic command definition:
      • ON UPDATE <referential action>
      • <referential action> ::= CASCADE|SET NULL
    • <referential action> is placeholder
    • CASCADE|SET NULL is placeholder definition (placeholder value must be one of these choices)
  • Management Studio
    • Microsoft GUI for most SQL Server operations
      • Additional applications manage overall server security, business intelligence
    • Separate application from SQL Server
      • Uses a connection to send commands and capture results
      • SQL Server is not something we’ll work with directly