Skip to main content

Altering Tables ( Drop Tables )


DROP TABLE removes one or more tables. All table data and the table definition are  removed, so  be
careful with this statement!

 DROP [TEMPORARY] TABLE [IF EXISTS] table1; 

Use IF EXISTS to prevent an error from occurring for tables that do not exist. An error is generated for
each non-existent table when using IF EXISTS.

The TEMPORARY keyword has the following effects:
              1.  The statement drops only TEMPORARY tables.
              2.  The statement does not end an ongoing transaction

Using TEMPORARY is a good way to ensure that non-TEMPORARY table is not deleted by accident.

DROP TABLE examples: 
DROP TABLE table1; 
DROP TABLE IF EXISTS table1; 
DROP TEMPORARY TABLE eu_countries_temp; 

Comments

Popular posts from this blog

PHP INTRODUCTION

                     PHP  (recursive acronym for  PHP: Hypertext Preprocessor ) is a widely-used open source general-purpose scripting language that is especially suited for web development and can be embedded into HTML. PHP stands for  P HP:  H ypertext  P reprocessor PHP is a server-side scripting language, like ASP PHP scripts are executed on the server PHP supports many databases (MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc.) PHP is an open source software PHP is free to download and use Why PHP? PHP runs on different platforms (Windows, Linux, Unix, etc.) PHP is compatible with almost all servers used today (Apache, IIS, etc.) PHP is FREE to download from the official PHP resource:  www.php.net PHP is easy to learn and runs efficiently on the server side What can PHP do? Anything. PHP is mainly focused on server-side scripting, so you can...

Self Joins

A table name is always ambiguous when table is joined to itself using a self-join. For example, the Country table in the world database contains an IndepYear column indicating the year in which each country achieved independence. To find all countries that have the same year of independence as some given country, a self-join can be used. However, the query cannot be written like this: mysql> SELECT IndepYear, Name, Name -> FROM Country JOIN Country -> ON IndepYear = IndepYear AND Name = 'Qatar'; ERROR 1066 (42000): Not unique table/alias: 'Country' Furthermore, the ambiguity cannot be removed from column references by preceding them with table name qualifiers because the names remain identical: mysql> SELECT Country.IndepYear, Country.Name, Country.Name -> FROM Country JOIN Country -> ON Country.IndepYear = Country.IndepYear -> AND Country.Name = 'Qatar'; ERROR 1066 (42000): Not unique table/alias: 'Country' It ...