CS 111 – Nov. 8 Databases Database Management Systems (DBMS) Structured Query Language (SQL) Commitment –Please review sections 9.1 – 9.2.

Database A file containing 1+ tables Table = 2-d arrangement of data into rows and columns –Rows correspond to “records” – info about 1 customer, 1 student, 1 animal, 1 house, whatever –Columns correspond to “fields” – individual attributes about each record. For example, name, address, phone number, ID number, $ amount

DBMS “Data Base Management System” Software that allows us to manipulate a database file. Most often, we want to query the database. Examples: –Microsoft Access –Open Office Base –phpMyAdmin –Oracle –Datatel SQL = Structured Query Language –All DBMS support SQL –We use SQL to communicate with the database.

SQL “Structured Query Language” DBMS accepts commands written in this language, so we can manipulate the database file. DBMS may actually have point-&-click shortcut features to save time on tedious tasks, such as entering all the data, or creating tables from scratch. Most common SQL command is the “select” statement, which asks the DBMS to return some of the data in the database. Examples: –Show me everybody’s address –How many employees make over $100,000 ?

How to begin Create the database file Create first table: specify its format –For each field (column), it needs a name, data type and maximum length. –Common data types are: –Int/number –Date –Varchar (“variable-length character string”). Here you must specify a maximum length, such as 20 characters. –Sometimes, you may want to indicate whether a field is required, must have unique values, etc. Enter data into the table. Make queries about the table.

Example FirstLastLocationTitleSalary PeterJacobsBrusselsBroker55000 DeniseLambertBrusselsAccountant42500 RobertNijsBrusselsBroker66700 RuthMolloyChicagoManager68650 DeclanMurphyChicagoAccountant84125 SusanPattersonChicagoEconomist51000 RachelBradyCincinnatiBroker43300 DavidCunninghamCincinnatiAccountant48000 JohnWhelanCincinnatiBroker60500 YvonneButlerSan DiegoBroker48500 VeronicaKeatingSan DiegoBroker72000 MaryWalshDublinAccountant46850 An Employee table:

The select statement Very commonly used in SQL. Some possible formats: select columns from table; select * from table; select columns from table where condition; Examples: select First, Last from Employee; select Last, Location, Salary from Employee; select Last, Salary from Employee where Salary >= 70000; select * from Employee where Location = “Dublin”; select * from Employee where Last like “M%”;

Aggregate functions In SQL, we can ask questions that involve arithmetic, such as finding the max, min, avg of numerical values. select max(Salary) from Employee; select min(Salary), max(Salary) from Employee; select avg(Salary) from Employee where Location = “Chicago”; select avg(Salary) from Employee where Title = “Broker”;