Home > Articles

  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

Selecting, Creating, Dropping, and Altering Databases

MySQL provides several database-level statements: USE for selecting a default database, CREATE DATABASE for creating databases, DROP DATABASE for removing them, and ALTER DATABASE for modifying global database characteristics.

Note: From MySQL 5.0.2 on, you can use the keyword SCHEMA as a synonym for DATABASE in any statement where the latter occurs.

Selecting Databases

The USE statement selects a database to make it the default (current) database for a given connection to the server:

USE db_name;

You must have some access privilege for the database or you cannot select it.

It is not strictly necessary to select a database explicitly. If you have access to a database, you can use its tables without selecting it if you use qualified names that identify both the database and the table. For example, to retrieve the contents of the president table in the sampdb database without selecting the database first, write the query like this:

SELECT * FROM sampdb.president;

However, it's much more convenient to refer to tables without having to specify a database qualifier.

Selecting a database doesn't mean that it must be the default for the duration of the connection. You can issue any number of USE statements to switch back and forth among databases. Nor does selecting a database limit you to using tables only from that database. While one database is the default, you can refer to tables in other databases by qualifying their names with the appropriate database identifier.

When your connection to the server terminates, any notion by the server of which database was the default for the connection disappears. That is, if you connect to the server again, it doesn't remember what database you had selected previously.

Creating Databases

To create a database, use a CREATE DATABASE statement:

CREATE DATABASE db_name;

The conditions on database creation are that the name must be a legal identifier, the database must not already exist, and you must have sufficient privileges to create it.

When you create a database, the MySQL server creates a directory under its data directory that has the same name as the database. The new directory is called the database directory. The server also creates a db.opt file in the database directory to store database attributes.

CREATE DATABASE supports several optional clauses. The full syntax is as follows:

CREATE DATABASE [IF NOT EXISTS] db_name
 [CHARACTER SET charset] [COLLATE collation];

The options have the following meanings:

  • Normally, an error occurs if you try to create a database that already exists. To suppress this error and create a database only if it does not already exist, add an IF NOT EXISTS clause:

  • CREATE DATABASE IF NOT EXISTS db_name;
  • You can use the CHARACTER SET and COLLATE clauses to set the database default character set and collation. For example:

  • CREATE DATABASE mydb CHARACTER SET utf8 COLLATE utf8_icelandic_ci;

    The character set and collation attributes are stored in the db.opt file. They are used when you create a new table: If the table definition does not specify its own default character set and collation, the database defaults become the table defaults.

    If CHARACTER SET is given without COLLATE, the default collation for the character set is used. If COLLATE is given without CHARACTER SET, the first part of the collation name determines the character set. If no character set or collation is specified, the database defaults are taken from the server default character set and collation.

    The character set must be one of those supported by the server, such as latin1 or sjis. The collation should be a legal collation for the character set. For further discussion of character sets and collations, see Chapter 3.

To see the definition for an existing database, use a SHOW CREATE DATABASE statement:

mysql> SHOW CREATE DATABASE mydb\G
*************************** 1. row ***************************
       Database: mydb
Create Database: CREATE DATABASE ´mydb´
                 /*!40100 DEFAULT CHARACTER SET utf8
                 COLLATE utf8_icelandic_ci */

Dropping Databases

Dropping a database is just as easy as creating one, assuming that you have sufficient privileges:

DROP DATABASE db_name;

The DROP DATABASE statement is not something to use with wild abandon. It removes the database and all tables within it, so the database is gone forever unless you have been making backups regularly. In other words, don't try this statement just to see how it works unless you don't care about the database contents.

A database is represented by a directory under the data directory, and the directory is intended for storage of table data. If a DROP DATABASE statement fails, the reason most likely is that the database directory contains non-table files. DROP DATABASE will not delete such files, and as a result will not delete the directory, either. This means that the database directory continues to exist (albeit empty of any tables) and will show up if you issue a SHOW DATABASES statement. To really drop the database if this occurs, manually remove any remaining files in the database directory and the directory itself.

Altering Databases

The ALTER DATABASE statement makes changes to a database's global attributes. Currently, the only such attributes are the default character set and collation:

ALTER DATABASE db_name [CHARACTER SET charset] [COLLATE collation];

The earlier discussion for CREATE DATABASE describes the effect of the optional CHARACTER SET and COLLATE clauses.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020