PHP

Basic SQL

definition: Database A database which structures data in the form of tables. Each table contains information relevant to a particular feature, and is linked to other tables by a common value. For example, two attribute tables could be linked to a spatial data table via a Geocode, such as the postcode.

A very short explanation In one database. There are many tables. One table represents a set of entity. For example ‘People’, ‘Cars’, ‘Movies’ Table has many rows. One row in table represents instance of entities. For example Toni Meechai’, ‘Kobota Sedan’, ‘Twilight’ Table also has many column. One column represents property of an instance. For example Nationality’, ‘How fast’, ‘How boring it is’ When you want get or do something with Database Tables, you can query it like ‘Please show me all people’. Unfortunately, you have to follow SQL format.

Play with PHP MyAdmin Pay attention to demonstration. Try to understand ideas of ‘Database’, ‘Table’, ‘Row’, ‘Basic usage of SQL’. Learners can follow this article:

SQL : Selecting data

Selecting from 1 table SELECT * FROM COUNTRY; SELECT * FROM COUNTRY WHERE CONTINECT=‘ASIA’; SELECT CODE,NAME,CONTINENT,POPULATION FROM COUNTRY WHERE CONTINENT=‘ASIA’;

SELECT NAME,POPULATION FROM COUNTRY WHERE CONTINENT=‘ASIA’ ORDER BY POPULATION DESC; If we want to reverse it, change DESC to ASC instead

If it has many rows, we want just 10 rows SELECT NAME,POPULATION FROM COUNTRY WHERE CONTINENT=‘ASIA’ ORDER BY POPULATION DESC LIMIT 10;

If we want to change column name SELECT NAME AS “ ประเทศ สุ่ม ” FROM COUNTRY WHERE CONTINENT=‘ASIA’ ORDER BY RAND() LIMIT 10; NOTE, If you want to change name to be something like ประเทศ สุ่ม, it will throws an error Because that word contains whitespace.

List all countries started with ‘t’ SELECT NAME FROM COUNTRY WHERE NAME LIKE ‘T%’; List all countries ended with ‘land’ SELECT NAME FROM COUNTRY WHERE NAME LIKE ‘%land’; List all countries contains ‘ko’ SELECT NAME FROM COUNTRY WHERE NAME LIKE ‘%ko%’;

Tables joining Why joining? Refer to database course. It is better to store different content into different table. Reducing data redundant. MySQL, a database server we use is a Relational engine. We can say one table can has relationship to other tables. To get data across tables, we have to do joining selection.

Relationship in our 3 tables Consider our 3 tables: Country, City, CountryLanguage Table: Country has column ‘Code’ Table: City has column ‘CountryCode’ Table: CountryLanguage has column ‘CountryCode’ Country.Code, City.CountryCode, CountryLanguage.CountryCode are sharing relationship.

List all city in Thailand SELECT * FROM CITY,COUNTRY WHERE CODE=‘THA’ AND CODE=COUNTRYCODE; Remember. To join 2 tables we have to do 2 things. 1)Include 2 tables’name in From clause 2)Match the related columns in each 2 tables by using equality in where clause

If we have same columns name in 2 tables, you will get error cause there are ambiguous column names. To fix this problem, specific table name before column name by using.(dot) SELECT CITY.NAME,COUNTRY.NAME FROM CITY,COUNTRY WHERE CODE=‘THA’ AND COUNTRY.CODE=CITY.COUNTRYCODE;

Count and Sum Find surface area of Thailand + Malaysia SELECT SUM(SURFACEAREA) FROM COUNTRY WHERE NAME=‘THAILAND’ OR NAME=‘MALAYSIA’;

Find how many cities located in Asia SELECT COUNT(CITY.NAME) FROM CITY,COUNTRY WHERE CONTINENT=‘ASIA’ AND COUNTRY.CODE=CITY.COUNTRYCODE;

Changing Data Using SQL INSERT / UPDATE / DELETE

Prepare table first. CREATE TABLE Student ( id bigint(20) auto_increment PRIMARY KEY, varchar(255), firstname varchar(255), lastname varchar(255), nick varchar(255) );

Inserting — 1. Use SQL: “DESCRIBE tablename” to see the target table’s structure. Remember column name, type and sequence 2. Use SQL: “INSERT INTO VALUES(xxx,yyy,zzz)” Replace xxx,yyy,zzz with actual values you want to insert ordering as the table column’s sequence.

INSERT INTO student values( 1, ‘Taw’, ‘Poldee’, ‘Tawny’ );"

Updating — Updating SQL syntax is UPDATE tablename SET columnanme = newvalue WHERE condition

UPDATE student SET nick=‘Tawjung’ WHERE id=1;

Deleting Deleting SQL syntax is DELETE FROM tablename WHERE condition.

DELETE FROM student WHERE firstname=‘Taw’;

PHP interface with MySQL <?php mysql_connect("localhost:portnum", "user","password") or die(mysql_error()); mysql_select_db("dbname") or die(mysql_error()); $result = mysql_query("SELECT column1,column2 FROM tablename") or die(mysql_error()); while($row = mysql_fetch_array($result)) { print $row['column1']; print $row['column2']; } ?>