Lab 13 Databases and SQL

Useful information Last lab of the semester . Next week there will be a lab exam . No assignments for this lab.

Databases Data : facts and statistics collected together for reference or analysis Database : A database is a collection of one or more relations, where each relation is a table with rows and columns RDBMS : It contains a set of relations

Database Table attributes (or columns) customer_name customer_street customer_city Jones Smith Curry Lindsay Main North Park Harrison Rye Pittsfield tuples (or rows)

RDBMS Relation: made up of 2 parts: Instance : a table , with rows and columns. #Rows = cardinality, #fields = degree / arity. Schema : specifies name of relation, plus name and type of each column. E.G. Students(sid: string, name: string, login: string, age: integer, gpa: float )

SQL –Structured Query Langauage Developed by IBM (system R) in the 1970s Vendors Oracle MYSQL MS-SQL server IBM DB2

SQL –Structured Query Langauage Activity I : SELECT Tutorial from BBC TABLE http://sqlzoo.net/1.htm Hint: SELECT >>FROM >>WHERE SELECT is the data extraction operator.You can choose the attributes here (columns),’ * ‘ returns all the columns from the table FROM :Table name is defined here. WHERE : It is used to limit the rows according to the condition/s.

SQL –Structured Query Langauage Activity I : SELECT Tutorial from BBC TABLE 2.Relational operators same as c++ =(no double sign here like c++) ,>,<,<=,>=,!= Note :there is no operator like !< .Just use > instead 3.per capita GDP is the GDP divided by the population GDP/population Calculations are usually done in select clause .A new column is created with the calculation .It is a better practice to use an alias for a calculated column . Aliases : Aliases are defined in the from clause, called in select and where clauses . Eg.Select t.id from table as t ( Alternatively used as “from table t” without “as”.Here we create a new column called percaptaGDP using the formula) .

SQL –Structured Query Langauage Activity I : SELECT Tutorial from BBC TABLE 4. SQL aggregate functions returns a single value, calculated from values in a column. Useful aggregate functions: Used on column with quantitative data AVG() - Returns the average value COUNT() - Returns the number of rows ROUND()-Returns after rounding the number MAX() - Returns the largest value MIN() - Returns the smallest value SUM() - Returns the sum

SQL –Structured Query Langauage Activity I : SELECT Tutorial from BBC TABLE 6. The SQL LIKE Operator The LIKE operator is used to search for a specified pattern in a column. SQL LIKE Syntax: SELECT column name(s) FROM table name WHERE column name LIKE pattern; % operator is used inside the like operator. Ex. ‘%United’–Returns strings which ends with with United ‘United%’ -Returns string which starts with United ‘%United%’-Returns string which contains Unitedanywhere in the field.

SQL –Structured Query Langauage Activity I : SELECT Tutorial from BBC TABLE 5.The IN Operator The IN operator allows you to specify multiple values in a WHERE clause. SQL IN Syntax SELECT column_name(s) FROM table_name WHERE column_name IN (value1,value2,...);

SQL –Structured Query Langauage ActIivity 2:More practice with SELECT: Additional practice of the basic features using a table of Nobel Prize winners. http://sqlzoo.net/1b.htm

SQL joins An SQL JOIN clause is used to combine rows from two or more tables, based on a common field between them. The most common type of join is: SQL INNER JOIN (simple join). An SQL INNER JOIN returns all rows from multiple tables where the join condition is met. http://sqlzoo.net/3.htm

Questions?