CHAPTER II- INTRODUCTION TO STRUCTURED QUERY LANGUAGE
WHAT IS SQLyog?
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SQLyog provides you with powerful means to manage your MySQL databases.
Is a GUI tool for the RDBMS MySQL
Developed by Webyog, Inc.
trusted by 2.5 million users around the world.
Database Connection
Making a New Connection
After you start SQLyog, you have to enter the details of MySQL server you want to connect to. You must
connect to a MySQL server before you can perform any activities with the software.
If you are using SQLyog for the first time then you have to first create an instance
of your database connection. You can do this by clicking on New button in the connection
manager dialog
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New- Click the new button. In the name field (figure shown right) type the name by which you will
recognize the connection. By default SQLyog will create an instance with default values (e.g.
localhost, root).
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Save- This button allows you to save any change in the connection details.
DeleteClick this button to Delete the currently selected connection. Click Yes to Delete.
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Rename- Click the rename button to rename a connection. Note that Connection Names are names
used internally by SQLyog only (and not MySQL). Connection Names are used by SQLyog for storing
the connection details. Also, certain SQLyog functionalities will make use of the connection name as
stored by SQLyog.
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SQLyog USER INTERFACE
Status Bar
 Title Bar
The title bar shows the connection name and the host name of current connection.
 Object Browser
This window gives you complete details of the server you are connected to in a tree format. Expanding
database node will show the table(s), view(s), store procedure(s), function(s), trigger(s) and event(s) in
the database and expanding the table name node will show the columns and indexes available for the
table. You may Show/Hide Object Browser through Ctrl+SHift+1 buttons.
When you right click on any object in the Object Browser, you will get a context sensitive popup menu.
The options in the popup menu allow you to perform different operations on the selected object.
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 SQL Window
Here you write your SQL commands that you want to execute.
 Result Window
This window shows Results of Query which you can edit in an easy to use Excel like grid interface.
It also shows you information about Databases and Tables and all the query(s) that has been executed in
the current connection. The window has three permanent tabs - Data, Object and History and two context
specific tabs - Result and Message.
Message Tab
It shows the information about the various query(s) executed (e.g. number of row(s) returned/
updated / modified etc.) All those data are as they are returned in the 'status message' sent by the MySQL
server after (successful or unsuccessful) execution of the query, but before transmission of data has
started.
 Status Bar
The status bar is divided into 5 parts showing information about 1. General Information: Information about work being done in SQLyog, description of the menu item
selected.
2. Process Time: Time taken (in hh:mm:ss:ms) to execute the query i.e. Execution time and Total
time. Note: In HTTP connection only Total time is displayed.
3. Number of rows in the currently selected Resultset.
4. Line number and column number in which the cursor is located in different Edit windows.
5. Number of connections which have been made in SQLyog.
Executing SQL Queries
You can execute queries in SQLyog in following four ways:
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Execute Current Query: To execute a particular query in a batch, just place the cursor on the query
to be executed (i.e. before the semicolon separating the query from the next query). Select Edit ->
Execute Query -> Execute Current Query (or press F9 or click the 'single green arrow' icon in the
icon bar). Only the current query would be executed.
Execute All Queries: To execute the whole batch of queries entered in the SQL window. Select Edit
-> Execute Query -> Execute All Queries (or press Shift+F9 or click the 'double green arrow' icon
in the icon bar). All queries would be executed one by one, showing result set in separate tab window.
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Introduction to SQL
SQL is a standard language for accessing and manipulating databases.
What is SQL?
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SQL stands for Structured Query Language
SQL lets you access and manipulate databases
SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the
International Organization for Standardization (ISO) in 1987
What Can SQL do?
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SQL can execute queries against a database
SQL can retrieve data from a database
SQL can insert records in a database
SQL can update records in a database
SQL can delete records from a database
SQL can create new databases
SQL can create new tables in a database
SQL can create stored procedures in a database
SQL can create views in a database
SQL can set permissions on tables, procedures, and views
SQL is a Standard - BUT....
Although SQL is an ANSI/ISO standard, there are different versions of the SQL language.
However, to be compliant with the ANSI standard, they all support at least the major commands (such
as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.
The SQL CREATE DATABASE Statement
The CREATE DATABASE statement is used to create a new SQL database.
Syntax
CREATE DATABASE databasename;
CREATE DATABASE Example
The following SQL statement creates a database called "testDB":
Example
CREATE DATABASE testDB;
The SQL CREATE TABLE Statement
The CREATE TABLE statement is used to create a new table in a database.
Syntax
CREATE TABLE table_name (
column1 datatype,
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column2 datatype,
column3 datatype,
....
);
The column parameters specify the names of the columns of the table.
The datatype parameter specifies the type of data the column can hold (e.g. varchar, integer, date,
etc.).
SQL CREATE TABLE Example
The following example creates a table called "Persons" that contains five columns: PersonID, LastName,
FirstName, Address, and City:
Example
CREATE TABLE Persons (
PersonID int,
LastName varchar(255),
FirstName varchar(255),
Address varchar(255),
City varchar(255)
);
The PersonID column is of type int and will hold an integer.
The LastName, FirstName, Address, and City columns are of type varchar and will hold characters, and
the maximum length for these fields is 255 characters
The SQL INSERT INTO Statement
The INSERT INTO statement is used to insert new records in a table.
INSERT INTO Syntax
It is possible to write the INSERT INTO statement in two ways.
The first way specifies both the column names and the values to be inserted:
INSERT INTO table_name (column1, column2, column3, ...)
VALUES (value1, value2, value3, ...);
INSERT INTO Example
The following SQL statement inserts a new record in the "Customers" table:
Example
INSERT INTO Customers (CustomerName, ContactName, Address, City, PostalCode, Country)
VALUES ('Cardinal', 'Tom B. Erichsen', 'Skagen 21', 'Stavanger', '4006', 'Norway');
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CHAPTER III- ADVANCED DATA DEFINITION COMMANDS
SQL ALTER TABLE Statement
The ALTER TABLE statement is used to add, delete, or modify columns in an existing table.
The ALTER TABLE statement is also used to add and drop various constraints on an existing table.
ALTER TABLE - ADD Column
To add a column in a table, use the following syntax:
ALTER TABLE table_name
ADD column_name datatype;
The following SQL adds an "Email" column to the "Customers" table:
Example
ALTER TABLE Customers
ADD Email varchar(255);
ALTER TABLE - DROP COLUMN
To delete a column in a table, use the following syntax (notice that some database systems don't allow
deleting a column):
ALTER TABLE table_name
DROP COLUMN column_name;
The following SQL deletes the "Email" column from the "Customers" table:
Example
ALTER TABLE Customers
DROP COLUMN Email;
ALTER TABLE - ALTER/MODIFY COLUMN
To change the data type of a column in a table, use the following syntax:
ALTER TABLE table_name
MODIFY COLUMN column_name datatype;
Change Data Type Example
Now we want to change the data type of the column named "DateOfBirth" in the "Persons" table.
We use the following SQL statement:
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ALTER TABLE Persons
MODIFY COLUMN DateOfBirth varchar (40);
Example
ALTER TABLE Persons
MODIFY COLUMN DateOfBirth year;
ADD MULTIPLE COLUMNS IN TABLE
Syntax
To add multiple columns to an existing table, the SQL ALTER TABLE syntax is:
ALTER TABLE table_name
ADD (column_1 datatype,
column_2 datatype,
...
column_n datatype);
Example
Let's look at SQL ALTER TABLE example that adds more than one column.
For example:
ALTER TABLE supplier
ADD (supplier_name char(50),
city char(45));
This SQL ALTER TABLE example will add two columns, supplier_name as a char(50) field and city as a
char(45) field to the supplier table.
RENAME COLUMN IN TABLE
Syntax
To rename a column in an existing table, the SQL ALTER TABLE syntax is:
For Oracle and PostgreSQL:
ALTER TABLE table_name
CHANGE COLUMN old_name TO new_name;
Example:
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ALTER TABLE supplier
CHANGE COLUMN supplier_name sname VARCHAR(100);
RENAME TABLE
Syntax
To rename a table, the SQL ALTER TABLE syntax is:
ALTER TABLE table_name
RENAME TO new_table_name;
Example
Let's look at an example that renames a table called supplier to the new name vendor.
ALTER TABLE supplier RENAME TO vendor;
The SQL UPDATE Statement
The UPDATE statement is used to modify the existing records in a table.
UPDATE Syntax
UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
UPDATE Table
The following SQL statement updates the first customer (CustomerID = 1) with a new contact
person and a new city.
Example
UPDATE Customers
SET ContactName = 'Alfred Schmidt', City= 'Frankfurt'
WHERE CustomerID = 1;
The selection from the "Customers" table will now look like this:
Custo
merID
Customer
Name
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ContactName
Address
City
Postal
Code
Country
1
Alfreds
Futterkiste
Alfred Schmidt
Obere Str. 57
Frankfurt
12209
Germany
2
Ana Trujillo
Emparedad
os y
helados
Ana Trujillo
Avda. de la
Constitución
2222
México
D.F.
05021
Mexico
3
Antonio
Moreno
Taquería
Antonio Moreno
Mataderos 2312
México
D.F.
05023
Mexico
4
Around the
Horn
Thomas Hardy
120 Hanover Sq.
London
WA1
1DP
UK
5
Berglunds
snabbköp
Christina
Berglund
Berguvsvägen 8
Luleå
S-958
22
Sweden
UPDATE Multiple Records
It is the WHERE clause that determines how many records will be updated.
The following SQL statement will update the contactname to "Juan" for all records where country is
"Mexico":
Example
UPDATE Customers
SET ContactName='Juan'
WHERE Country='Mexico';
The selection from the "Customers" table will now look like this:
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Custom
erID
CustomerNa
me
ContactName
Addre
ss
City
PostalC
ode
Country
1
Alfreds
Futterkiste
Alfred Schmidt
Obere Str. 57
Frankfurt
12209
Germany
2
Ana Trujillo
Emparedados
y helados
Juan
Avda. de la
Constitución
2222
México D.F.
05021
Mexico
3
Antonio
Moreno
Taquería
Juan
Mataderos
2312
México D.F.
05023
Mexico
4
Around the
Horn
Thomas Hardy
120 Hanover
Sq.
London
WA1
1DP
UK
5
Berglunds
snabbköp
Christina Berglund
Berguvsväge
n8
Luleå
S-958 22
Sweden
SQL TRUNCATE TABLE
The TRUNCATE TABLE statement is used to delete the data inside a table, but not the table itself.
Syntax
TRUNCATE TABLE table_name;
Example
TRUNCATE TABLE Customers
The SQL DROP TABLE Statement
The DROP TABLE statement is used to drop an existing table in a database.
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Syntax
DROP TABLE table_name;
Note: Be careful before dropping a table. Deleting a table will result in loss of complete information
stored in the table!
SQL DROP TABLE Example
The following SQL statement drops the existing table "Shippers":
Example
DROP TABLE Shippers;
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