Publishers of technology books, eBooks, and videos for creative people

Home > Articles

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

Choosing Your Column Types

Once you have identified all of the tables and columns that the database will need, you should determine each column’s data type. When you’re creating a table, MySQL requires that you explicitly state what sort of information each column will contain. There are three primary types, which is true for almost every database application:

  • Text (aka strings)

  • Numbers

  • Dates and times

Within each of these, there are many variants—some of which are MySQL specific. Choosing your column types correctly not only dictates what information can be stored and how, but also affects the database’s overall performance. Table 4.2 lists most of the available types for MySQL, how much space they take up, and brief descriptions of each type. Note that some of these limits may change in different versions of MySQL, and the character set (to be discussed in Chapter 6, “Database Design”) may also impact the size of the text types.

Table 4.2 MySQL Data Types

Type

Size

Description

CHAR[Length]

Length bytes

A fixed-length field from 0 to 255 characters long

VARCHAR[Length]

String length + 1 or 2 bytes

A variable-length field from 0 to 65,535 characters long

TINYTEXT

String length + 1 bytes

A string with a maximum length of 255 characters

TEXT

String length + 2 bytes

A string with a maximum length of 65,535 characters

MEDIUMTEXT

String length + 3 bytes

A string with a maximum length of 16,777,215 characters

LONGTEXT

String length + 4 bytes

A string with a maximum length of 4,294,967,295 characters

TINYINT[Length]

1 byte

Range of –128 to 127 or 0 to 255 unsigned

SMALLINT[Length]

2 bytes

Range of –32,768 to 32,767 or 0 to 65,535 unsigned

MEDIUMINT[Length]

3 bytes

Range of –8,388,608 to 8,388,607 or 0 to 16,777,215 unsigned

INT[Length]

4 bytes

Range of –2,147,483,648 to 2,147,483,647 or 0 to 4,294,967,295 unsigned

BIGINT[Length]

8 bytes

Range of –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 or 0 to 18,446,744,073,709,551,615 unsigned

FLOAT[Length, Decimals]

4 bytes

A small number with a floating decimal point

DOUBLE[Length, Decimals]

8 bytes

A large number with a floating decimal point

DECIMAL[Length, Decimals]

Length + 1 or 2 bytes

A DOUBLE stored as a string, allowing for a fixed decimal point

DATE

3 bytes

In the format YYYY-MM-DD

DATETIME

8 bytes

In the format YYYY-MM-DD HH:MM:SS

TIMESTAMP

4 bytes

In the format YYYYMMDDHHMMSS; acceptable range starts in 1970 and ends in the year 2038

TIME

3 bytes

In the format of HH:MM:SS

ENUM

1 or 2 bytes

Short for enumeration, which means that each column can have one of several possible values

SET

1, 2, 3, 4, or 8 bytes

Like ENUM except that each column can have more than one of several possible values

Many of the types can take an optional Length attribute, limiting their size. (The brackets, [ ], indicate an optional parameter to be put in parentheses.) For performance purposes, you should place some restrictions on how much data can be stored in any column. But understand that attempting to insert a string five characters long into a CHAR(2) column will result in truncation of the final three characters. Only the first two characters would be stored; the rest would be lost forever. This is true for any field in which the size is set (CHAR, VARCHAR,INT, etc.). Thus, your length should always correspond to the maximum possible value—as a number—or the longest possible string—as text—that might be stored.

The various date types have all sorts of unique behaviors, the most important of which you’ll learn about in this book. All the behaviors are documented in the MySQL manual. You’ll use the DATE and TIME fields primarily without modification, so you do not have to worry too much about their intricacies.

There are also two special types—ENUM and SET—that allow you to define a series of acceptable values for that column. An ENUM column can store only one value of a possible several thousand, whereas SET allows for several of up to 64 possible values. These are available in MySQL but aren’t present in every database application.

To select the column types:

  1. Identify whether a column should be a text, number, or date/time type (Table 4.3).

    Table 4.3 users Table

    Column Name

    Type

    user_id

    number

    first_name

    text

    last_name

    text

    email

    text

    pass

    text

    registration_date

    date/time

    This is normally an easy and obvious step, but you want to be as specific as possible. For example, the date 2006-08-02 (MySQL format) could be stored as a string—August 2, 2006. But if you use the proper date format, you’ll have a more useful database (and, as you’ll see, there are functions that can turn 2006-08-02 into August 2, 2006).

  2. Choose the most appropriate subtype for each column (Table 4.4).

    Table 4.4 users Table

    Column Name

    Type

    user_id

    MEDIUMINT

    first_name

    VARCHAR

    last_name

    VARCHAR

    email

    VARCHAR

    pass

    CHAR

    registration_date

    DATETIME

    For this example, user_id is set as a MEDIUMINT, allowing for up to nearly 17 million values (as an unsigned, or non-negative, number). registration_date will be a DATETIME. It can store both the date and the specific time a user registered. When deciding among the date types, consider whether you’ll want to access just the date, the time, or possibly both.

    When choosing a subtype, err on the side of storing too much information.

    The other fields will be mostly VARCHAR, since their lengths will differ from record to record. The only exception is the password column, which will be a fixed-length CHAR (you’ll see why when inserting records in the next chapter). See the sidebar “CHAR vs. VARCHAR” for more information on these two types.

  3. Set the maximum length for text columns (Table 4.5).

    Table 4.5 users Table

    Column Name

    Type

    user_id

    MEDIUMINT

    first_name

    VARCHAR(20)

    last_name

    VARCHAR(40)

    email

    VARCHAR(60)

    pass

    CHAR(128)

    registration_date

    DATETIME

    The size of any field should be restricted to the smallest possible value, based on the largest possible input. For example, if a column stores a state abbreviation, it would be defined as a CHAR(2). Other times you might have to guess: I can’t think of any first names longer than about 10 characters, but just to be safe I’ll allow for up to 20.

  • + Share This
  • 🔖 Save To Your Account

Peachpit Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Peachpit 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 Peachpit 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 ask@peachpit.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 Adobe Press. 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.peachpit.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