Quick and Dirty Databases(and SQL)

Chris Warrencwarren@williams.edux4323 Jesup 312

Data Organization in Databases

field (a.k.a. column)a bunch of fields make a

record (a.k.a. row)a bunch of records make a

tablea bunch of tables make a

databasea bunch of databases make a

DB system

Designing a (Relational) DB

1.Entities and Entity Relationships (ERD)

2.Normalizing

3.Detailing

4.Cleanup

Entities and Entity Relationships

• Entities (tables)– ID (a.k.a. primary key)

– Entity Attributes (fields)

• Relationships– 1-to-1

– 1-to-many or many-to-1

– many-to-many

Relationships

• 1-to-1– usually data is in the same table

• 1-to-many and many-to-1– foreign key goes with the many entity

• many-to-many– linking table with 2 foreign keys, one for each side

Create an ERD

ERD = Entity Relationship Diagram

• Draw on paper

• Entities (tables)

• Relationships between them– indicate type : 1-to-1, 1-to-many, many-to-

many

Detail the ERD

Finalize table names and list fields

• table name should be plural

• primary id is singular + _id

• add any foreign keys

• list fields– include unit in name– add is_ or flag_ or _flag for true/false fields

Normalizing

Normalizing is basically removing duplication

• merge mostly similar tables

• split out common field sets

• split out conceptually distinct field sets

Normalizing – Merge Tables

• tables have very similar field sets• entities are both / all examples of a more

general concept

1. generalize the table name

2. add a type field

3. change foreign keys in other tables to

include the type

Normalizing – Split Out Field Sets

• same list of field repeated in different tables

• group of fields describes a distinct concept

1. create a new table for that new entity2. add a foreign key to the new table in each of the

original tables

Normalizing – Split Out Concepts

• a table has multiple sub-parts– common field name prefix is one indicator

• data would be repeated for many records

1. create a new table for those fields

2. add a foreign key to the original

table

ERD Detailing

• create any grouping tables as needed

• add data types and descriptions to fields– int– varchar (string up to 255 characters)– text (BIG string)– date and/or time– boolean (true/false)

ERD Cleanup

• add timestamps (created_at,

updated_at)

• review relationships, fix as needed

• review fields, add any missing

characteristics

ERD is DONE!

Now you get to implement it...

SQL – Structured Query Language

• used to send commands to a database• there’s a core standard, and a lot of

vendor-specific minor changes / additions

• two branches– data definition – create tables– data manipulation – add, edit, retrieve, delete

data

• http://dev.mysql.com/doc/refman/5.0/en/

SQL concepts (manipulation)

1. Databases are a big pile of information

2. Identify which piece of info you want to manipulate

3. State how you want to manipulate it– retrieve it– edit it– delete it– add it

Writing SQL

build it backwards....

1. what you want to do – select, update, delete, or insert

2. where it is– the table and row(s)

3. the specific parts– the fields

SQL Conventions

• SQL keywords in upper case

• Your info (tables, fields, etc) in lower case

• Indent each section of the statement

• Use multiple lines

SQL SELECT (most common)

SELECTfields

FROMtables

WHEREconditions

GROUP BYnon-aggregate fields

ORDER BYfields

3. the SELECT clause – which fields

1. the FROM clause – which tables

2. the WHERE clause – which rows

SQL SELECT Example

SELECTe.name

FROMcwarren_equipment AS e,cwarren_location AS l

WHEREe.location_id=l.location_id

AND l.name=‘Lab 54’;

SQL SELECT Example

SELECTe.name

FROMcwarren_equipment AS eJOIN cwarren_location AS l ON

e.location_id=l.location_idWHERE

l.name=‘Lab 54’;

SQL UPDATE

UPDATE TABLE tableSET

field1=newval1,field2=newval2,...

WHEREconditions

SQL INSERT

INSERT INTO tableVALUES (v1,v2,v3,...)

NOTE: use the special value NULL for id columns

INSERT INTO tableVALUES (NULL,v1,v2,v3,...)

SQL DELETE

DELETE FROM tableWHERE

conditions

NOTE: DANGEROUS!

SQL Gotchas

• quote text values• do NOT quote number values• always specify table links• separate using commas

• FORMAT WELL!!

SQL Manual

http://dev.mysql.com/doc/refman/5.0/en/