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Data Types in SQL/MySQL

Objectives

To understand different data types in SQL/MySQL

THEORY

Properly defining the fields in a table is important to the overall optimization of your database. You should use only the type and size of field you really need to use; don't define a field as 10 characters wide if you know you're only going to use 2 characters. These types of fields (or columns) are also referred to as data types, after the type of data you will be storing in those fields. Not all data types are supported by every relational database vendor.

For example, the Oracle database doesn’t support DATETIME and MySQL doesn’t support CLOB data type. So while designing database schema and writing SQL queries, make sure to check if the data types are supported or not.

Data types listed here don’t include all the data types, these are the most popularly used data types. Some relational database vendors have their own data types that might be not listed here. For example, Microsoft SQL Server has money and small-money data types but since it’s not supported by other popular database vendors, it’s not listed here.

Every relational database vendor has its own maximum size limit for different data types, you don’t need to remember the limit. The idea is to have the knowledge of what data type to be used in a specific scenario.

MySQL uses many different data types broken into three categories:

Numeric Data Type

Date and Time Data Type

Character string Data Type

Unicode Character and String Data Types

Binary Data Types

Miscellaneous Data Types

Numeric Data Type

MySQL uses all the standard ANSI SQL numeric data types, so if you're coming to MySQL from a different database system, these definitions will look familiar to you.

The following list shows the common numeric data types use in SQL/MySQL:

INT :

A normal-sized integer that can be signed or unsigned. If signed, the allowable range is from -2147483648 to 2147483647. If unsigned, the allowable range is from 0 to 4294967295. You can specify a width of up to 11 digits.

TINYINT :

A very small integer that can be signed or unsigned. If signed, the allowable range is from -128 to 127. If unsigned, the allowable range is from 0 to 255. You can specify a width of up to 4 digits.

SMALLINT :

A small integer that can be signed or unsigned. If signed, the allowable range is from -32768 to 32767. If unsigned, the allowable range is from 0 to 65535. You can specify a width of up to 5 digits.

MEDIUMINT :

A medium-sized integer that can be signed or unsigned. If signed, the allowable range is from -8388608 to 8388607. If unsigned, the allowable range is from 0 to 16777215. You can specify a width of up to 9 digits.

BIGINT :

A large integer that can be signed or unsigned. If signed, the allowable range is from -9223372036854775808 to 9223372036854775807. If unsigned, the allowable range is from 0 to 18446744073709551615. You can specify a width of up to 20 digits.

FLOAT(M, D) :

A floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D). This is not required and will default to 10,2, where 2 is the number of decimals and 10 is the total number of digits (including decimals). Decimal precision can go to 24 places for a FLOAT.

DOUBLE(M,D) :

A double-precision floating-point number that cannot be unsigned. You can define the display length (M) and the number of decimals (D). This is not required and will default to 16,4, where 4 is the number of decimals. Decimal precision can go to 53 places for a DOUBLE. REAL is a synonym for DOUBLE.

DECIMAL(M,D) :

An unpacked floating-point number that cannot be unsigned. In unpacked decimals, each decimal corresponds to one byte. Defining the display length (M) and the number of decimals (D) is required. NUMERIC is a synonym for DECIMAL.

Date and Time Types:

The following list shows the common Date and Time Types use in SQL/MySQL:

DATE :

A date in YYYY-MM-DD format, between 1000-01-01 and 9999-12-31. For example, December 30th, 1973 would be stored as 1973-12-30.

DATETIME :

A date and time combination in YYYY-MM-DD HH:MM: SS format, between 1000-01-01 00:00:00 and 9999-12-31 23:59:59. For example, 3:30 in the afternoon on December 30th, 1973 would be stored as 1973-12-30 15:30:00.

TIMESTAMP :

A timestamp between midnight, January 1, 1970, and sometime in 2037. This looks like the previous DATETIME format, only without the hyphens between numbers; 3:30 in the afternoon on December 30th, 1973 would be stored as 19731230153000 ( YYYYMMDDHHMMSS ).

TIME :

Stores the time in HH:MM: SS format.

YEAR(M) :

Stores a year in 2-digit or 4-digit format. If the length is specified as 2 (for example YEAR(2)), YEAR can be 1970 to 2069 (70 to 69). If the length is specified as 4, YEAR can be 1901 to 2155. The default length is 4.

Character and String Data Types:

Although numeric and date types are fun, most data you'll store will be in string format. This list describes the common string datatypes in MySQL.

CHAR(M) :

A fixed-length string between 1 and 255 characters in length (for example CHAR(5)), right-padded with spaces to the specified length when stored. Defining a length is not required, but the default is 1.

VARCHAR(M) :

A variable-length string between 1 and 255 characters in length; for example VARCHAR(25). You must define a length when creating a VARCHAR field.

BLOB or TEXT :

A field with a maximum length of 65535 characters. BLOBs are "Binary Large Objects" and are used to store large amounts of binary data, such as images or other types of files. Fields defined as TEXT also hold large amounts of data; the difference between the two is that sorts and comparisons on stored data are case sensitive on BLOBs and are not case sensitive in TEXT fields. You do not specify a length with BLOB or TEXT.

TINYBLOB / TINYTEXT :

A BLOB or TEXT column with a maximum length of 255 characters. You do not specify a length with TINYBLOB or TINY TEXT.

MEDIUMBLOB or MEDIUMTEXT :

A BLOB or TEXT column with a maximum length of 16777215 characters. You do not specify a length with MEDIUMBLOB or MEDIUM TEXT.

LONGBLOB or LONGTEXT :

A BLOB or TEXT column with a maximum length of 4294967295 characters. You do not specify a length with LONGBLOB or LONGTEXT.

ENUM :

An enumeration, which is a fancy term for a list. When defining an ENUM, you are creating a list of items from which the value must be selected (or it can be NULL). For example, if you wanted your field to contain "A" or "B" or "C", you would define your ENUM as ENUM ('A', 'B', 'C') and only those values (or NULL) could ever populate that field.

Unicode Character and String Data Type's

The following list shows the common Date and Time Types use in SQL/MySQL

NCHAR :

fixed length with a maximum length of 4000 characters

NVARCHAR :

Variable-length storage with a maximum length of 4000 characters

NVARCHAR(max) :

Variable-length storage with provided max characters

NTEXR :

Variable-length storage with a maximum size of 1GB of data

Binary Data Type's

The following list shows the common Binary Data Type's use in SQL/MySQL

BINARY :

fixed length with a maximum length of 8000 bytes

VARBINARY :

Variable-length storage with a maximum length of 8000 bytes

VARBINARY(max) :

Variable-length storage with provided max bytes

IMAGE :

Variable-length storage with a maximum size of 2GB binary data

Miscellaneous Data Type's

The following list shows the common Miscellaneous Data Type's use in SQL/MySQL

CLOB :

Character large object that can hold up to 2GB

BLOB :

for binary large object

XML :

for storing xml data

JSON :

for storing JSON data