Intro to SQL

CS-422

Dick Steflik

Structured Query Language

• Developed by C. Date for Relational Data Base Management Systems (RDBMS)

• Simple Declarative Language– has no program control statements

SQL

• Two categories of commands– Data Manipulation Commands

• deal with:– RETRIEVING DATA

– MAINTAINING DATA

• ADDING, UPDATING, DELETING

– Data Definition Commands• DEAL WITH:

– CREATING DATABASE OBJECTS (TABLES,VIEWS)

– Object organization and attributes

Data Model

• Database objects are modeled on the concept of a table (i.e. rows and columns)– Each row is a single table object– Columns are the attributes of that table

• A database is a collection of related tables

Referential Integrity

• Rules to insure that table data stays accurate and accessible– rows in a table should be unique

• one column should contain no duplicate data

• primary key

– column values cannot contain repeating groups or arrays

– null is different than space and zero, 2 null values are not considered equal

Data Manipulation Commands

• Select - query and display data from a database

• Insert - a new row into a table

• Update - modify a column in a table

• Delete a row from a table

Select

• Select (column list) from (sources) where (conditions) order by (ocolumn list)• column list - comma separated list of names of columns to be in output

– Ex. ssn , lastname , firstname,gpa– can contain literals to be included in output

• Ex. Ssn,”~”,lastname,”~”,firstname

• sources - name(s) of table(s) to retrieve data from• conditions (optional) - conditions for selections

– lastname like “S%”– (lastname = “Steflik) and (firstname like “R%”)

• ocolumn list (optional)- list of columns that output should be ordered by• Ex

– select * from student– select lastname,fristname from student where gpa > 3.0– select lastname,firstname from student order by lastname,firstname

Select - joined tables

• Two tables may be joined and viewed as a single data source is the both have a common column

• suppose we have 2 tables: Inventory and category and each has a column called catg_code

• In category catg_code is unique and is the primary key

Select - joined tables (cont.)

P_no Catg_code qty Catg_code descr

Inventory Category

join

Select - joined tables (cont.)

• To retrieve all of the part numbers and the name of the category to which the part belongs:

– select inventory.p_no category.descr from inventroy , category– select a.p_no,” “,b.descr from a inventory , b category

Insert

• Add a row to a table– insert into category values(“IGN”,”Ignition System”)

• use jdbc execute Update method– ex. Stmt.executeUpdate(“insert into Category values(‘IGN’,’Ignition System’)”);

Update

• Modify an existing row in a table– update category set descr = “Ignition Subsystem” where catg_code = “IGN”

• Use jdbc executeUpdate method – String s = “update category set descr = ‘Ignition Subsystem’ where catg_code =

‘IGN’ ”;– stmt.executeUpdate(s);

Delete

• Remove a row from a table– delete from category where catg_code = “IGN”

• remove the IGN category

– delete from category where catg_code like “I%”

• remove all rows where catg_code starts with an “I”

Data Definition Commands

• Create table– add a table to a database

• Drop Table– remove a table from a database

• Alter Table– add or delete column(s)

A good reference

• Phil Greenspun – SQL for Web Nerds– http://philip.greenspun.com/sql/