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3 sql overview

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3 sql overview

  1. 1. SQL Overview CIS-182
  2. 2. 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…)
  3. 3. 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
  4. 4. 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
  5. 5. Types of SQL Statements • Data Definition Language (DDL): Create/edit objects – CREATE, ALTER • Data Control Language (DCL): Specify access and permissions – GRANT, REVOKE • Data Manipulation Language (DML): Work with data – SELECT * FROM Employees – INSERT INTO Students
  6. 6. 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
  7. 7. 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)
  8. 8. 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
  9. 9. 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
  10. 10. 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
  11. 11. 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: ,
  12. 12. 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)
  13. 13. 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

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