MySQL Introduction PDF

3 Assi.Prof. JOHN MICHAEL LEGASPI Faculty, Computer and Electronics Department  Objectives Start MySQL and learn how to use the MySQL Reference Manual Create a database Change (activate) a database Create tables using MySQL Create and run SQL commands in MySQL ...

3 Assi.Prof. JOHN MICHAEL LEGASPI Faculty, Computer and Electronics Department  Objectives Start MySQL and learn how to use the MySQL Reference Manual Create a database Change (activate) a database Create tables using MySQL Create and run SQL commands in MySQL  Objectives (continued) Identify and use data types to define columns in tables Understand and use nulls Add rows to tables View table data Correct errors in a database  Objectives (continued) Save SQL commands and results to a file Describe a table’s layout using MySQL  Introduction Structured Query Language (SQL): – Popular and widely used language for retrieving and manipulating database data – Developed in mid-1970s under the name SEQUEL – Renamed SQL in 1980 – Used by most DBMSs  Introduction to MySQL Starting MySQL Obtaining help Accessing the MySQL Reference Manual  Starting MySQL Windows XP – Click Start button – Point to All Programs – Point to MySQL on menu – Point to MySQL Server 4.1 – Click MySQL Command Line Client Must enter password in Command Line Client window  Obtaining Help in MySQL Type \h at MySQL> prompt Type “help” followed by name of command – help contents – help union  Using MySQL Reference Manual to Get Help Click MySQL Manual - Table of Contents on MySQL 4.1 submenu Can access online  Creating a Database Must create a database before creating tables Use CREATE DATABASE command Include database name Creating a Database (continued) Changing the Default Database Default database: database to which all subsequent commands pertain USE command, followed by database name: – Changes the default database – Execute at the start of every session  Creating a Table Describe the layout of each table in the database Use CREATE TABLE command TABLE is followed by the table name Follow this with the names and data types of the columns in the table Data types define type and size of data  Table and Column Name Restrictions Names cannot exceed 18 characters Must start with a letter Can contain letters, numbers, and underscores (_) Cannot contain spaces Creating the REP Table  Entering Commands in MySQL Commands are free-format; no rules stating specific words in specific positions Press ENTER to move to the next line in a command Indicate the end of a command by typing a semicolon Commands are not case sensitive Running SQL Commands  Editing SQL Commands Statement history: stores most recently used command Editing commands: – Use arrow keys to move up, down, left, and right – Use Ctrl+A to move to beginning of line – Use Ctrl+E to move to end of line – Use Backspace and Delete keys Errors in SQL Commands  Editing MySQL Commands Press Up arrow key to go to top line Press Enter key to move to next line if line is correct Use Right and Left arrow keys to move to location of error Press ENTER key when line is correct If Enter is not pressed on a line, line not part of the revised command  Dropping a Table Can correct errors by dropping (deleting) a table and starting over Useful when table is created before errors are discovered Command is followed by the table to be dropped and a semicolon Any data in table also deleted  Data Types For each table column, type of data must be defined Common data types: – CHAR(n) – VARCHAR(n) – DATE – DECIMAL(p,q) – INT – SMALLINT  Nulls A special value to represent situation when actual value is not known for a column Can specify whether to allow nulls in the individual columns Should not allow nulls for primary key columns  Implementation of Nulls Use NOT NULL clause in CREATE TABLE command to exclude the use of nulls in a column Default is to allow null values If a column is defined as NOT NULL, system will reject any attempt to store a null value there  Adding Rows to a Table INSERT command: – INSERT INTO followed by table name – VALUES command followed by specific values in parentheses – Values for character columns in single quotation marks The Insert Command Modifying the INSERT Command To add new rows modify previous INSERT command Use same editing techniques as those used to correct errors Adding Additional Rows The INSERT Command with Nulls Use a special format of INSERT command to enter a null value in a table Identify the names of the columns that accept non- null values, then list only the non-null values after the VALUES command  The INSERT Command with Nulls Enter only non-null values Precisely indicate values you are entering by listing the columns The INSERT Command with Nulls (continued)  Viewing Table Data Use SELECT command to display all the rows and columns in a table SELECT * FROM followed by the name of the table Ends with a semicolon Viewing Table Data (continued) Viewing Table Data (continued)  Correcting Errors In the Database UPDATE command is used to update a value in a table DELETE command allows you to delete a record INSERT command allows you to add a record Correcting Errors in the Database UPDATE: change the value in a table DELETE: delete a row from a table Correcting Errors in the Database (continued) Correcting Errors in the Database (continued)  Saving SQL Commands Allows you to use commands again without retyping Different methods for each SQL implementation you are using – Oracle SQL*Plus and SQL*Plus Worksheet use a script file – Access saves queries as objects – MySQL uses an editor to save text files  Saving SQL Commands Script file: – File containing SQL commands – Use a text editor or word processor to create – Save with a.txt file name extension – Run in MySQL: SOURCE file name \. file name – Include full path if file is in folder other than default  Creating the Remaining Database Tables Execute appropriate CREATE TABLE and INSERT commands Save these commands to a secondary storage device Describing a Table  Summary Use MySQL Command Line Client window to enter commands Type \h or help to obtain help at the mysql> prompt Use MySQL Reference Manual for more detailed help  Summary (continued) Use the CREATE DATABASE command to create a database Use the USE command to change the default database Use the CREATE TABLE command to create tables Use the DROP TABLE command to delete a table  Summary (continued) CHAR, VARCHAR, DATE, DECIMAL, INT and SMALLINT data types Use INSERT command to add rows Use NOT Null clause to identify columns that cannot have a null value Use SELECT command to view data in a table  Summary (continued) Use UPDATE command to change the value in a column Use DELETE command to delete a row Use SHOW COLUMNS command to display a table’s structure