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Introduction to Structured Query Language (SQL)

Introduction to Structured Query Language (SQL). Origins & history. Early 1970’s – IBM develops Sequel as part of the System R project at its San Hose Research Lab; 1986 - ANSI & ISO publish the standard SQL-86;

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Introduction to Structured Query Language (SQL)

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  1. Introduction to Structured Query Language (SQL)

  2. Origins & history Early 1970’s – IBM develops Sequel as part of the System R project at its San Hose Research Lab; 1986 - ANSI & ISO publish the standard SQL-86; 1987 – IBM publishes its own “standard” SQL called Systems Architecture Database Interface (SAA-SQL); 1989 – SQL-89 published by ANSI (extended version of SQL-86); 1992 – SQL-92 published with better support for algebraic operations; 1999 – SQL-1999 published with support for typing, stored procedures, triggers, BLOBs etc. SQL-92 remains the most widely implemented standard – and most database vendors also provide their own (proprietary) extensions.

  3. Components of SQL The SQL language has several parts: • Data-definition language (DDL). The SQL DDL provides commands for defining relation schemas, deleting relations, and modifying relation schemas. • Interactive data-manipulation language (DML). The SQL DML includes a query language based on both the relational algebra and the tuple relational calculus. It includes also commands to insert tuples into, delete tuples from, and modify tuples in the database. • View definition. The SQL DDL includes commands for defining views. • Transaction control. SQL includes commands for specifying the beginning and ending of transactions. • Embedded SQL and dynamic SQL. Embedded and dynamic SQL define how SQL statements can be embedded within general-purpose programming languages, such as C, C++, Java, PL/I, Cobol, Pascal, and Fortran. • Integrity. The SQL DDL includes commands for specifying integrity constraints that the data stored in the database must satisfy. Updates that violate integrity constraints are disallowed. • Authorization. The SQL DDL includes commands for specifying access rights to relations and views.

  4. SQL Example (1) • The Supplier-and-Parts Database sp s p

  5. SQL Example (2) • Project the columns renamed columns: SELECT sname FROM s SELECT sname AS Supplier, status * 5 AS 'Status times Five' FROM s computed columns: SELECT sname, status * 5 FROM s

  6. SQL Example (3) • Restrict the rows SELECT * FROM s WHERE city=‘London’ complex condition: SELECT * FROM s WHERE city=‘London’ OR status = 30

  7. SQL Example (4) • Restrict & Project SELECT city FROM s WHERE sname='smith' OR status='20' remove duplicate rows: SELECT DISTINCT city FROM s WHERE sname='smith' OR status='20'

  8. SQL Example (4) Group By and Having • Use the ‘GROUP BY’ clause to aggregate related rows SELECT city, SUM(status) AS 'Total Status' FROM s GROUP BY city Use the ‘HAVING’ clause to restrict rows aggregated with ‘GROUP BY’ SELECT city, SUM(status) AS 'Total Status' FROM s GROUP BY city HAVING SUM(status) > 30

  9. SQL Functions • SQL provides a wide range of predefined functions to perform manipulation of data. • Four types of functions arithmetic (sqrt(), log(), mod(), round() …) date (sysdate(), month(), dayname() …) character (length(), lower(), upper()…) aggregate (min(), max(), avg(), sum() …)

  10. Joins (1) • The m-f Database m f

  11. Joins (3) • Product (or Cartesian Product) SELECT * FROM m, f Synonymous with the CROSS JOIN, hence: SELECT * FROM m CROSS JOIN f; would return the same result. This is not very useful but is the basis for all other joins.

  12. Joins (4) • Natural join Joins tables using some shared characteristic – usually (but not necessarily) a foreign key. SELECT * FROM m,f WHERE m.age = f.age

  13. Joins (5) • Inner joins The previous example, besides being a natural join, is also an example of an inner join. An inner join retrieves data only from those rows where the join condition is met. SELECT * FROM m,f WHERE m.age > f.age

  14. Joins (6) • Outer joins Unmatched rows can be included in the output using as outer join. Left outer join: SELECT * FROM m LEFT OUTER JOIN f ON m.age = f.age Right outer join: SELECT * FROM m RIGHT OUTER JOIN f ON m.age = f.age

  15. Joins (7) • Self Join Special case of the inner join – here the table employee shows employees and their managers. Ruth manages Joe who manages Tom, Dick and Harry. Show who manages who by name: SELECT E1.emp_name AS Employee, E2.emp_name AS ManagerFROM employee AS E1INNER JOIN employee AS E2 ON E1.mgr_id = E2.emp_id

  16. Bibliography / Readings / Home based activities Bibliography • An Introduction to Database Systems (8th ed.), C J Date, Addison Wesley 2004 • Database Management Systems, P Ward & G Defoulas, Thomson 2006 • Database Systems Concepts (4th ed.), A Silberschatz, H F Korth & S Sudarshan, McGraw-Hill 2002 Readings • Introduction to SQL’ McGraw-Hill/Osbourne (handout) Home based activities • Ensure you download xampp and install on home PC or laptop (if you have a slow home internet connection – download to data key or CD here at UWE) • Copy the SQL Workbook onto your data key or CD. • Import the tables from the SQL Workbook into your home MySQL DB. Begin working through some of the query examples in the workbook using PHPMyAdmin.

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