SQL commands are instructions used to communicate with the database to perform specific task that work with data. SQL commands can be used not only for searching the database but also to perform various other functions like, for example, you can create tables, add data to tables, or modify data, drop the table, set permissions for users. SQL commands are grouped into four major categories depending on their functionality:
Subquery or Inner query or Nested query is a query in a query. A subquery is usually added in the WHERE Clause of the sql statement. Most of the time, a subquery is used when you know how to search for a value using a SELECT statement, but do not know the exact value. Subqueries are an alternate way of returning data from multiple tables. Subqueries can be used with the following sql statements along with the comparision operators like =, <, >, >=, <= etc.
The SQL command in this recipe removes a column and the column’s data from an existing MySQL table. To delete the column col_stuff from the table table_things , use the following SQL command: ALTER TABLE 'table_things' DROP 'col_stuff' Please reward our authors by sharing their hard work...
MySQL tables are easy to extend with additional columns. To add a column called email to the contacts table created in Create a basic MySQL table with a datatype of VARCHAR(80), use the following SQL statement: ALTER TABLE contacts ADD email VARCHAR(60); This first statement will add the email column to the end of the table.
A Database Management System (DBMS) sometimes called a database manager or database system is a set of computer programs that controls the creation, organization, maintenance, and retrieval of data from the database stored in a computer. It allows the individuals or entities to easily access and use the data from database. An excellent database system helps the end users to easily access and use the data and also stores the new data in a systematic way.
A Trigger is a named database object which defines some action that the database should take when some databases related event occurs. Triggers are executed when you issues a data manipulation command like INSERT, DELETE, UPDATE on a table for which the t A Trigger is a named database object which defines some action that the database should take when some databases related event occurs. Triggers are executed when you issues a data manipulation command like INSERT, DELETE, UPDATE on a table for which the trigger has been created. They are automatically executed and also transparent to the user. But for creating the trigger the user must have the CREATE TRIGGER privilege.
Question #2 from the September MySQL User Group was whether or not a TRIGGER can affect a different table. Apparently the documentation (perhaps for an earlier version??) specified this was not possible. Tom Hanlon, MySQL employee, put up this example (modified from the original, special thanks to Ralph Navarro for copying it down):
It depends on what type of variable you setup. It's better to set it as system variable. The way to do it is like this: set max_allowed_packet=1000*1024*1024; set net_buffer_length=1000000; To check if they're set, use: select @@max_allowed_packet; Note that the @@ operator works in global scope when setting up a variable, while when fetching a variable, it will retrieve the session one and if it's not found, the global one.
MySQL is a widely spread SQL database management system mainly used on LAMP (Linux/Apache/MySQL/PHP) projects. In order to be able to use a database, one needs to create: a new database, give access permission to the database server to a database user and finally grant all right to that specific database to this user. This tutorial will explain how to create a new database and give a user the appropriate grant permissions. For the purpose of this tutorial, I will explain how to create a database and user for the music player Amarok . In order to index its music collection, Amarok quand use a mysql backend.
MySQL is deployed in 9 of the top 10 most trafficked sites on the web including Facebook, Twitter, eBay and YouTube, as well as in some of the fastest growing services such as Tumblr, Pinterest and box.com Working with these companies has given MySQL developers, consultants and support engineers unique insight into how to design database-driven web architectures – whether deployed on-premise or in the cloud. The MySQL Web Reference Architectures are a set of documented and repeatable best practices for building infrastructure that deliver the highest levels of scalability, agility and availability with the lowest levels of cost, risk and complexity.