Skip to main content

About MySQL, Databases and SQL Commands

About MySQL, Databases and SQL Commands

In the last post we ‘created a database’ from our script as an example to test the working of MySQL. Actually a database is a set of tables for storing data. The tables in a database may be logically related with each other. MySQL supports unlimited number of databases and for each application you may use a different one

To understand relation between a database and tables consider an example of a database oriented Note Keeping application. Since it needed user authorization we can store user information such as username and password in one table, upgrading that system to multi-user capable is also possible because a table can store any number of rows (i.e. different set of username & password, in this case). We’ll also need a second table for storing note data. Thus we’re using a database having two tables to store data related to a single application.

The following image illustrates this relation quite well:

How tables are organised in a database

MySQL database server supports the creation, storing and retrieval of data using the Structured Query Language. SQL is quite easy to understand and work with, probably because it is very much plain English. Below I’m stating a few useful SQL commands:


It creates a database named ‘temp’. We discussed about it in the post Installing, Configuring and Testing MySQL Database Server on 'localhost'


It creates a table inside a database. The database to be worked with should first be selected using the following PHP command:


it could be run after first creating the database through a SQL query. After selection of database the following SQL query will create a table inside that database (since a table is not an independent entity).

CREATE TABLE one (id INT, name VARCHAR(20));

The above query creates a table ‘one’ with two data fields id of type integer and name of type character (20 characters long). This table can hold any number of data.


After creation of table we can insert data into it with the following SQL query:

INSERT INTO one (id, name) VALUES (1,’PHP’);


It is used to request data form a table.


It will request all (*) the rows from the table ‘one’.

NOTE: Though SQL commands end with a ‘;’ semicolon, you don’t have to have it when querying database from PHP. SQL commands from PHP works both in UPPER and lower case.

Previous Articles:

Popular posts from this blog

Fix For Toshiba Satellite "RTC Battery is Low" Error (with Pictures)

RTC Battery is Low Error on a Toshiba Satellite laptop "RTC Battery is Low..." An error message flashing while you try to boot your laptop is enough to panic many people. But worry not! "RTC Battery" stands for Real-Time Clock battery which almost all laptops and PCs have on their motherboard to power the clock and sometimes to also keep the CMOS settings from getting erased while the system is switched off.  It is not uncommon for these batteries to last for years before requiring a replacement as the clock consumes very less power. And contrary to what some people tell you - they are not rechargeable or getting charged while your computer or laptop is running. In this article, we'll learn everything about RTC batteries and how to fix the error on your Toshiba Satellite laptop. What is an RTC Battery? RTC or CMOS batteries are small coin-shaped lithium batteries with a 3-volts output. Most laptops use

The Best Way(s) to Comment out PHP/HTML Code

PHP supports various styles of comments. Please check the following example: <?php // Single line comment code (); # Single line Comment code2 (); /* Multi Line comment code(); The code inside doesn't run */ // /* This doesn NOT start a multi-line comment block /* Multi line comment block The following line still ends the multi-line comment block //*/ The " # " comment style, though, is rarely used. Do note, in the example, that anything (even a multi-block comment /* ) after a " // " or " # " is a comment, and /* */ around any single-line comment overrides it. This information will come in handy when we learn about some neat tricks next. Comment out PHP Code Blocks Check the following code <?php //* Toggle line if ( 1 ) {      // } else {      // } //*/ //* Toggle line if ( 2 ) {      // } else {      // } //*/ Now see how easy it is to toggle a part of PHP code by just removing or adding a single " / " from th

Generating XML Feeds (RSS, Atom) Using PHP

RSS/ATOM feeds are very common these days and almost all Content Management Systems (CMS) can generate it. But in the case when you want to generate it yourself or just want to learn how you can, read on! Both RSS and ATOM feeds are written in eXtensible Markup Language (XML) standard markup. Not just standard markups, you also need to be sure of what and how you put data in those markup elements (tags). For all this refer to the feed specifications of RSS and ATOM . XML itself is very strict and the standard specifications makes it even harder to generate valid feeds. And moreover, why re-invent the wheel when we can have it – ready-made. The solution I'm referring to here is, to use a third-party Library – Universal FeedWriter. FeedWriter is a PHP class written by Anis uddin Ahmad that can dramatically  ease-off feeds (both RSS and Atom) generation. You can download this library from  here . Every feed should have at least the following data: Feed title URL(of the webs