Home > Articles

This chapter is from the book

This chapter is from the book

Character Set Support

Prior to MySQL 4.1, the server operates using a single character set at a time. As of MySQL 4.1, the server can support multiple character sets simultaneously, and character sets can be specified independently at the server, database, table, column, or string constant level. For example, if you want a table's columns to use latin1 by default, but also to include a Hebrew column and a Greek column, you can do that. In addition, you can explicitly specify collations (sorting orders). It is also possible to find out what character sets and collations are available, and to convert data from one character set to another.

This section provides general background on using MySQL's character set support. Chapter 3 provides more specific discussion of character sets, collations, binary versus non-binary strings, and how to define character-based table columns and work with them. Chapter 11 discusses how to configure which character sets the server makes available. That chapter also includes notes on what to do when upgrading older tables to MySQL 4.1 so that you can use the new features.

Character Set Support Before MySQL 4.1

Prior to MySQL 4.1, string values in MySQL have no explicit character set. Instead, string constants and column values always are interpreted with respect to the server's character set. By default, this is the character set selected when the server was built (usually latin1), but the built-in value may be overridden at runtime with the --default-character-set option. This is very simple but quite limiting. For example, you cannot have a table that stores values using different character sets for different columns.

The single-character-set model also can lead to index-related problems if you change the server's character set after having already created tables and loaded character data into them. These problems occur due to the fact that index values for character columns are stored in sorted order according to the collating sequence of the character set that happens to be in force at the time the index entries are created. Character sets have different collating sequences, so if you load a table while the server is using one character set and then reconfigure the server to use a different set, it's possible that the index entries no longer will be in the correct order with respect to the collating sequence of the new character set. Worse, if you add new rows to the table, the index that was initially created using the sort order of the original character set will be updated using the order of the new set. Consequently, index-based queries might not work correctly.

The solution to this problem is to rebuild the indexes for each existing table that has character-based indexes to use the collating order of the new character set. A table can be converted in various ways:

  • Dump the table with mysqldump, drop it, and reload it from the dump file. This operation causes the indexes to be rebuilt as the file is reloaded. It works for any storage engine.

  • Drop the indexes and add them again (for example, with ALTER TABLE, or with DROP INDEX and CREATE INDEX). This works for any storage engine, but requires that you know the exact index definitions so that you can re-create them properly.

  • For MyISAM tables, you can rebuild indexes by running myisamchk with the --recover and --quick options, together with a --set-character-set option that specifies the character set to use. Equivalent alternatives are to use the mysqlcheck program with the --repair and --quick options, or a REPAIR TABLE statement with the QUICK option. mysqlcheck and REPAIR TABLE are more convenient because the server does the work and it knows which character set to use. myisamchk must be run with the tables offline and you have to specify the character set explicitly.

Despite the methods available for reordering indexes if you change the server's character set, the fact that you need to do it at all is a bother. MySQL 4.1 eliminates the need. Each character column is associated with a character set and collation that determines its ordering, so if you change the server character set, it has no impact on individual columns. Also, if you change a column's character set or collation, MySQL automatically reorders the indexes without manual intervention.

When you upgrade an older server to MySQL 4.1 or newer, your old tables can still be used but you should convert them to 4.1 format so that you can take full advantage of the improved character set support instituted in 4.1. Instructions for doing this can be found in "Upgrading Tables When Character Set Conversion Is Necessary," in Chapter 11.

Character Set Support in MySQL 4.1 and Up

In MySQL 4.1, character set support was revised considerably to provide the following features:

  • The server supports use of multiple character sets simultaneously.

  • Unicode support is provided by the utf8 and ucs2 character sets.

  • You can specify character sets at the server, database, table, column, and string constant level, not just at the server level:

    • CREATE DATABASE allows you to assign the database character set, and ALTER DATABASE allows you to change it.

    • CREATE TABLE and ALTER TABLE have clauses for table- and column-level character set assignment. (Details are given in Chapter 3.)

  • Functions and operators are available for converting individual values from one character set to another or for determining the character set of a value.

  • A given character set can have one or more collations. You can choose the collation most appropriate for your applications.

  • The COLLATE operator can be used to alter the collation of a string and the COLLATION() function returns the collation of a string.

  • The SHOW CHARACTER SET and SHOW COLLATION statements list the available character sets and collations.

  • The server automatically reorders indexes when you change the collation of an indexed character column.

You cannot mix character sets within a string, or use different character sets for different rows of a given column. However, by using a Unicode character set (which represents the encodings for many languages within a single character set), you may be able to implement multi-lingual support of the type you desire.

Specifying Character Sets

Character set and collation assignments can be made at several levels, from the default used by the server to the character set used for individual strings.

The server's default character set and collation are built in at compile time. You can override them at server startup time by using the --character-set-server and --collation-server options. If you specify only the character set, its default collation becomes the server's default collation. If you specify a collation, it must be compatible with the character set. (A collation is compatible with a character set if its name begins with the character set name. For example, utf8_danish_ci is compatible with utf8 but not with latin1.)

In SQL statements that create databases and tables, two clauses are used for specifying database, table, and column character set and collation values:

COLLATE collation

charset is the name of a character set supported by the server, and collation is the name of one of the character set's collations. These clauses can be specified together or separately. If both are given, the collation name must be compatible with the character set. If only CHARACTER SET is given, its default collation is used. If only COLLATE is given, the character set is implicit in the first part of the character set name.

  • To specify a default character set and collation for a database when you create it, use this statement:

  • CREATE DATABASE db_name CHARACTER SET charset COLLATE collation;

    If no character set or collation is given, the server defaults are used for the database.

    To change a database default character set and collation, use this statement:

    ALTER DATABASE db_name CHARACTER SET charset COLLATE collation;
  • To specify a default character set and collation for a table, use CHARACTER SET and COLLATE table options at table creation time:

  • CREATE TABLE tbl_name (...) CHARACTER SET charset COLLATE collation;

    If no character set or collation is given, the database defaults are used for the table.

  • Columns in a table can be assigned a character set and collation explicitly with CHARACTER SET and COLLATE attributes. For example:

  • c CHAR(10) CHARACTER SET charset COLLATE collation

    If no character set or collation is given, the table defaults are used for the column. Data types for which these attributes may be given are CHAR, VARCHAR, TEXT, ENUM, and SET.

It's also possible to sort string values using a specific collation by using the COLLATE operator. For example, if c is a latin1 column that has the default collation of latin1_swedish_ci, but you want to order it using Spanish sorting rules, do this:

SELECT c FROM t ORDER BY c COLLATE latin1_spanish_ci;

Determining Character Set Availability and Current Settings

To find out which character sets and collations are available, use these statements:


Each of them supports a LIKE clause that narrows the results to those character set or collation names matching a pattern. For example, this statement lists the Latin-based character sets:

mysql> SHOW CHARACTER SET LIKE 'latin%';
| Charset | Description                 | Default collation | Maxlen |
| latin1  | ISO 8859-1 West European    | latin1_swedish_ci |      1 |
| latin2  | ISO 8859-2 Central European | latin2_general_ci |      1 |
| latin5  | ISO 8859-9 Turkish          | latin5_turkish_ci |      1 |
| latin7  | ISO 8859-13 Baltic          | latin7_general_ci |      1 |

This statement lists the collations available for the utf8 character set:

mysql> SHOW COLLATION LIKE 'utf8%';
| Collation          | Charset | Id  | Default | Compiled | Sortlen |
| utf8_general_ci    | utf8    | 33  | Yes     | Yes      |       1 |
| utf8_bin           | utf8    | 83  |         | Yes      |       1 |
| utf8_unicode_ci    | utf8    | 192 |         | Yes      |       8 |
| utf8_icelandic_ci  | utf8    | 193 |         | Yes      |       8 |
| utf8_latvian_ci    | utf8    | 194 |         | Yes      |       8 |
| utf8_romanian_ci   | utf8    | 195 |         | Yes      |       8 |
| utf8_slovenian_ci  | utf8    | 196 |         | Yes      |       8 |
| utf8_polish_ci     | utf8    | 197 |         | Yes      |       8 |
| utf8_estonian_ci   | utf8    | 198 |         | Yes      |       8 |
| utf8_spanish_ci    | utf8    | 199 |         | Yes      |       8 |
| utf8_swedish_ci    | utf8    | 200 |         | Yes      |       8 |
| utf8_turkish_ci    | utf8    | 201 |         | Yes      |       8 |
| utf8_czech_ci      | utf8    | 202 |         | Yes      |       8 |
| utf8_danish_ci     | utf8    | 203 |         | Yes      |       8 |
| utf8_lithuanian_ci | utf8    | 204 |         | Yes      |       8 |
| utf8_slovak_ci     | utf8    | 205 |         | Yes      |       8 |
| utf8_spanish2_ci   | utf8    | 206 |         | Yes      |       8 |

As can be seen in the output from these statements, each character set has at least one collation and one of them is its default collation.

To display the server's current character set and collation settings, use SHOW VARIABLES:

mysql> SHOW VARIABLES LIKE 'character\_set\_%';
| Variable_name            | Value  |
| character_set_client     | latin1 |
| character_set_connection | latin1 |
| character_set_database   | latin1 |
| character_set_results    | latin1 |
| character_set_server     | latin1 |
| character_set_system     | utf8   |
mysql> SHOW VARIABLES LIKE 'collation\_%';
| Variable_name        | Value             |
| collation_connection | latin1_swedish_ci |
| collation_database   | latin1_swedish_ci |
| collation_server     | latin1_swedish_ci |

Unicode Support

One of the reasons there are so many character sets is that different encodings have been developed for different languages. This presents several problems. For example, a given character that is common to several languages might be represented by different numeric values in different encodings. Also, different languages require different numbers of bytes to represent characters. The latin1 character set is small enough that every character fits in a single byte, but languages such as those used in Japan and China contain so many characters that they require multiple bytes per character.

The goal of Unicode is to provide a unified character-encoding system within which character sets for all languages can be represented in a consistent manner. In MySQL, Unicode support is provided through two character sets:

  • The ucs2 character set corresponds to the Unicode UCS-2 encoding. It represents each character using two bytes, most significant byte first. This character set does not represent characters that require more than two bytes. UCS is an abbreviation for Universal Character Set.

  • The utf8 character set has a variable-length format in which characters are represented using from one to three bytes. It corresponds to the Unicode UTF-8 encoding. (UTF-8 allows for encodings using up to four bytes, but the MySQL utf8 character set currently does not include any characters that use more than three bytes.) UTF is an abbreviation for UCS Transformation Format.

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.


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.


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.


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.


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


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


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.


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.


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