1 Session 6: Database Best Practice iNET Academy Open Source Web Development

2 Objectives Relational Databases Normalization and Forms of Normalization Backup and Restore Data Advanced SQL

3 Relational Databases In relational systems, data is spread across several tables. The key is the relation between tables Decision of the primary key is very important in designing database. Foreign key is key (one or more than one field) that acts as the primary key in one table. In other tables, they are normal columns, not the key.

4 Relationship Types One-to-One Relationship Each item is related to one and only one other item.

5 Relationship Types (cont.) One-to-Many Relationships: a key from one table appears multiple times in another table

6 Relationship Types (cont.) Many-to-Many Relationships

7 Normalization Goal: minimize the duplication of data

8 Forms of Normalization - First Normal Form Tables must not have repeating columns that contain the same kind of data All column must containt only one value There must be a primary key that uniquely defines rows

9 First Normal Form (cont.) The Address is splited into street, city, state, zip code

10 Second Normal Form Tables must be in First Normal Form Columns that have repeating values across multiple rows must be placed in separate tables and referenced by a key value in the original table

11 Second Normal Form (cont.)

12 Third Normal Form Remove partial dependence, data that is not fully dependent on the primary key, but dependent on another value in the table.

13 Column Data Types PHP isn’t strongly typed, but most databases are!

14 Backing Up & Restoring Data - Copying Database Files To backup, simple copy all files in the database’s directory. Shutdown the database server before backing up To restore a database, copy all files into the database’s directory. Then, restart the database server Note: File Backup & Restore must consider the problem of multiple versions of database server. Backingup and Restoring on *nix systems must consider the file permissions.

15 Backing Up & Restoring Data – Using mysqldump Command Syntax: mysqldump –u user –p objects_to_backup Backingup a database: mysqldump –u root –p store > my_backup_of_store.sql

16 Backing Up & Restoring Data – Using mysqldump Command (cont.) To backup a table mysqldump –u root –p store authors > authors.sql To backup everything mysqldump –u root –p - -all-databases > my_backup.sql To backup only the structure, not the data mysqldump –u root –p - -no-data store > structure.sql To backup only the data mysqldump –u root –p - -no-create-info store > data.sql

17 Backing Up & Restoring Data – Using mysqldump Command (cont.) Restoring a MySQL backup Restoring a full backup mysql –u root –p < my_backup.sql Restoring a database mysql –u root –p –D store < my_backup.sql Working with other formats: CSV format mysqldump –u root –p - -no-create-info - -tab=/home/jon - -fields-terminated-by=‘,’ store Using mysqlimport command to import data from other formats mysqlimport –u root –p - -fields-terminated-by=‘,’ store books.txt Backup best practice Determine how often to backup based on How critical is your data How often it changes Keep a copy of data in a separate location

18 Advanced SQL Indexes Use to find the data as quick as possible Indexes are used when In a WHERE clause: SELECT * FROM authors WHERE author=‘Ellen Sieve’; the author column should be indexed In an ORDER BY clause: SELECT * FROM contacts ORDER BY author; the author column should be indexed In MIN or MAX clauses How to create the index CREATE UNIQUE INDEX authind ON authors (author);

19 Advanced SQL (cont.) Multicolumn indexes: columns that are likely to be used in the WHERE clause should be indexed LEFT JOIN Clause SELECT fields FROM left_table LEFT JOIN right_table ON left_table.field_id = right_table.field_id GROUP BY Clause SELECT title, COUNT(author_id) FROM books NATURAL JOIN authors GROUP BY title

20 Advanced SQL (cont.) Using Database Functions String Functions: Concatenation Concatenation with a predefined separator

21 Advanced SQL (cont.) String functions Calculate a string length Changing strings to upper- or lowercase

22 Advanced SQL (cont.) String Functions Trimming and padding strings To trim spaces or tabs from a string, use LTRIM or RTRIM To trim spaces or a specified character, use TRIM function TRIM(LEADING ‘X’ FROM string) TRIM(TRAILING ‘X’ FROM string)

23 Advanced SQL (cont.) String Functions String location and position Cutting up strings LEFT RIGHT SUBSTRING

24 Advanced SQL (cont.) String Functions Search and Replace

25 Advanced SQL (cont.) Date and Time Functions

26 Advanced SQL (cont.) Date and Time Functions

27 Advanced SQL (cont.) Date and Time Functions

28 Advanced SQL (cont.) Date and Time Functions

29 Advanced SQL (cont.) Date and Time Functions