SQL Data Types
The data type of a column defines what value the column can hold: integer, character, money, date and time, binary, and so on.
Each column in a database table is required to have a name and a data type.
An SQL developer must decide what type of data that will be stored inside each column when creating a table. The data type is a guideline for SQL to understand what type of data is expected inside of each column, and it also identifies how SQL will interact with the stored data.
Always check the documentation! Data types might have different names in different databases. And even if the name is the same, the size and other details may be different!
MySQL Data Types (Version 8.4)
In MySQL there are three main data types: String, Numeric, and Date and Time.
String Data Types
| Data type | Description |
|---|---|
| CHAR(size) | A fixed-length string (can contain letters, numbers, and special characters). size specifies the column length in characters, from 0 to 255. Default size is 1 |
| VARCHAR(size) | A variable-length string (can contain letters, numbers, and special characters). size specifies the maximum column length in characters, from 0 to 65535 |
| BINARY(size) | Similar to CHAR(), but stores binary byte strings. size specifies the column length in bytes. Default size is 1 |
| VARBINARY(size) | Similar to VARCHAR(), but stores binary byte strings. size specifies the maximum column length in bytes. |
| BLOB(size) | A BLOB column with a maximum length of 65535 bytes |
| TINYBLOB | A BLOB column with a maximum length of 255 bytes |
| MEDIUMBLOB | A BLOB column with a maximum length of 16777215 bytes |
| LONGBLOB | A BLOB column with a maximum length of 4294967295 or 4GB bytes |
| TEXT(size) | Holds a string with a maximum length of 65535 bytes |
| TINYTEXT | A TEXT column with a maximum length of 255 characters |
| MEDIUMTEXT | A TEXT column with a maximum length of 16777215 characters |
| LONGTEXT | A TEXT column with a maximum length of 4294967295 or 4GB bytes |
| ENUM(val1, val2, val3, ...) | A string object that can have only one value, chosen from the list of possible values (val1, val2, val3,..). You can list up to 65535 values. If a value is inserted that is not in the list, a blank value will be inserted |
| SET(val1, val2, val3, ...) | A string object that can have zero or more values, chosen from the list of possible values (val1, val2, val3,..). You can list up to 64 values |
Numeric Data Types
| Data type | Description |
|---|---|
| BIT( size ) | A bit-value type. size indicates the number of bits per value, from 1 to 64. The default value for size is 1. |
| TINYINT( size ) | A very small integer. Signed range is from -128 to 127. Unsigned range is from 0 to 255. size specifies the minimum display width (max display width is 255) |
| BOOL | A value of zero is considered as false, nonzero values are considered as true. |
| BOOLEAN | Equal to BOOL |
| SMALLINT( size ) | A small integer. Signed range is from -32768 to 32767. Unsigned range is from 0 to 65535. size specifies the minimum display width (max display width is 255) |
| MEDIUMINT( size ) | A medium-sized integer. Signed range is from -8388608 to 8388607. Unsigned range is from 0 to 16777215. size specifies the minimum display width (max display width is 255) |
| INT( size ) | A normal-size integer. Signed range is from -2147483648 to 2147483647. Unsigned range is from 0 to 4294967295. size specifies minimum display width (max display width is 255) |
| INTEGER( size ) | Synonym for INT( size ) |
| BIGINT( size ) | A large integer. Signed range is from -9223372036854775808 to 9223372036854775807. Unsigned range is from 0 to 18446744073709551615. size specifies the minimum display width (max display width is 255) |
| DECIMAL( size , d ) | An exact fixed-point number. size indicates the total number of digits (max 65). d indicates the number of digits after the decimal point (max 30). The default value for size is 10. The default value for d is 0. |
| DEC( size , d ) | Synonym for DECIMAL( size , d ) |
| FLOAT( size , d ) | A small floating-point number. FLOAT( size , d ) is deprecated in MySQL 8.0.17, and it will be removed in future MySQL versions |
| FLOAT( p ) | A floating-point number. The p value determines whether to use FLOAT or DOUBLE for the resulting data type. If p is from 0 to 24, the data type becomes FLOAT. If p is from 25 to 53, the data type becomes DOUBLE |
| DOUBLE( size , d ) | A normal-size floating-point number. Permissible values are -1.7976931348623157E+308 to -2.2250738585072014E-308, 0, and 2.2250738585072014E-308 to 1.7976931348623157E+308. The total number of digits is specified in size . The number of digits after the decimal point is specified in the d parameter |
| DOUBLE PRECISION( size , d ) | Synonym for DOUBLE( size , d ) |
Date and Time Data Types
| Data type | Description |
|---|---|
| DATE | A date. Format: YYYY-MM-DD. The supported range is from '1000-01-01' to '9999-12-31' |
| DATETIME( fsp ) | A date and time combination. Format: YYYY-MM-DD hh:mm:ss. The supported range is from '1000-01-01 00:00:00' to '9999-12-31 23:59:59'. Adding DEFAULT and ON UPDATE in the column definition to get automatic initialization and updating to the current date and time |
| TIMESTAMP( fsp ) | A timestamp. Format: YYYY-MM-DD hh:mm:ss. TIMESTAMP values are stored as the number of seconds since the Unix epoch ('1970-01-01 00:00:00' UTC). The supported range is from '1970-01-01 00:00:01' UTC to '2038-01-09 03:14:07' UTC. Automatic initialization and updating to the current date and time can be specified using DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP in the column definition |
| TIME( fsp ) | A time. Format: hh:mm:ss. The supported range is from '-838:59:59' to '838:59:59' |
| YEAR | A year in a four-digit format (YYYY). Values allowed in four-digit format: 1901 to 2155, and 0000. |
SQL Server Data Types
In SQL Server there are three main data types: String, Numeric, and Date and Time.
String Data Types
| Data type | Description | Max char length | Storage |
|---|---|---|---|
| char(n) | Fixed-length non-Unicode character data (n must be between 1 and 8000) | 8,000 | n bytes (uses one byte for each character) |
| varchar(n) | Variable-length non-Unicode character data (n must be between 1 and 8000) | 8,000 | n bytes + 2 bytes |
| varchar(max) | Variable-length non-Unicode character data | up to 2 GB | |
| nchar(n) | Fixed-length Unicode character data (n must be between 1 and 4000) | 4,000 | 2 * n bytes (uses two bytes for each character) |
| nvarchar(n) | Variable-length Unicode character data (n must be between 1 and 4000) | 4,000 | 2 * n bytes + 2 bytes (uses two bytes for each character) |
| nvarchar(max) | Variable-length Unicode character data | up to 2 GB | |
| binary(n) | Fixed-length binary data (n must be between 1 and 8000) | 8,000 | n bytes |
| varbinary(n) | Variable-length binary data (n must be between 1 and 8000) | 8,000 | actual length of data entered + 2 bytes |
| varbinary(max) | Variable-length binary data | 2GB |
Numeric Data Types
| Data type | Description | Storage |
|---|---|---|
| bit | Integer that can be 0, 1, or NULL | |
| tinyint | Allows whole numbers from 0 to 255 | 1 byte |
| smallint | Allows whole numbers between -32,768 and 32,767 | 2 bytes |
| int | Allows whole numbers between -2,147,483,648 and 2,147,483,647 | 4 bytes |
| bigint | Allows whole numbers between -9,223,372,036,854,775,808 and 9,223,372,036,854,775,807 | 8 bytes |
| decimal(p,s) | Fixed precision and scale numbers. Allows numbers from -10^38 +1 to 10^38 â1. The p parameter indicates the maximum total number of digits that can be stored (both to the left and to the right of the decimal point). p must be a value from 1 to 38. Default is 18. The s parameter indicates the maximum number of digits stored to the right of the decimal point. s must be a value from 0 to p. Default value is 0 | 5-17 bytes |
| numeric(p,s) | Fixed precision and scale numbers. Allows numbers from -10^38 +1 to 10^38 â1. The p parameter indicates the maximum total number of digits that can be stored (both to the left and to the right of the decimal point). p must be a value from 1 to 38. Default is 18. The s parameter indicates the maximum number of digits stored to the right of the decimal point. s must be a value from 0 to p. Default value is 0 | 5-17 bytes |
| smallmoney | Monetary data from -214,748.3648 to 214,748.3647 | 4 bytes |
| money | Monetary data from -922,337,203,685,477.5808 to 922,337,203,685,477.5807 | 8 bytes |
| float(n) | Floating precision number data from -1.79E + 308 to 1.79E + 308. The n parameter indicates whether the field should hold 4 or 8 bytes. float(24) holds a 4-byte field and float(53) holds an 8-byte field. Default value of n is 53. | 4 or 8 bytes |
| real | Floating precision number data from -3.40E + 38 to 3.40E + 38 | 4 bytes |
Date and Time Data Types
| Data type | Description | Storage |
|---|---|---|
| date | Store a date only. From January 1, 0001 to December 31, 9999 | 3 bytes |
| time | Store a time only to an accuracy of 100 nanoseconds | 3-5 bytes |
| datetime | From January 1, 1753 to December 31, 9999 with an accuracy of 3.33 milliseconds | 8 bytes |
| datetime2 | From January 1, 0001 to December 31, 9999 with an accuracy of 100 nanoseconds | 6-8 bytes |
| smalldatetime | From January 1, 1900 to June 6, 2079 with an accuracy of 1 minute | 4 bytes |
| datetimeoffset | The same as datetime2 with the addition of a time zone offset | 8-10 bytes |
| timestamp | Stores a unique number that gets updated every time a row gets created or modified. The timestamp value is based upon an internal clock and does not correspond to real time. Each table may have only one timestamp variable |
Other Data Types
| Data type | Description |
|---|---|
| sql_variant | Stores up to 8,000 bytes of data of various data types, except text, ntext, and timestamp |
| uniqueidentifier | Stores a globally unique identifier (GUID) |
| xml | Stores XML formatted data. Maximum 2GB |
| cursor | Stores a reference to a cursor used for database operations |
| table | Stores a result-set for later processing |
MS Access Data Types
| Data type | Description | Storage |
|---|---|---|
| Text | Use for text or combinations of text and numbers. 255 characters maximum | |
| Memo | Memo is used for larger amounts of text. Stores up to 65,536 characters. Note: You cannot sort a memo field. However, they are searchable | |
| Byte | Allows whole numbers from 0 to 255 | 1 byte |
| Integer | Allows whole numbers between -32,768 and 32,767 | 2 bytes |
| Long | Allows whole numbers between -2,147,483,648 and 2,147,483,647 | 4 bytes |
| Single | Single precision floating-point. Will handle most decimals | 4 bytes |
| Double | Double precision floating-point. Will handle most decimals | 8 bytes |
| Currency | Use for currency. Holds up to 15 digits of whole dollars, plus 4 decimal places. Tip: You can choose which country's currency to use | 8 bytes |
| AutoNumber | AutoNumber fields automatically give each record its own number, usually starting at 1 | 4 bytes |
| Date/Time | Use for dates and times | 8 bytes |
| Yes/No | A logical field can be displayed as Yes/No, True/False, or On/Off. In code, use the constants True and False (equivalent to -1 and 0). Note: Null values are not allowed in Yes/No fields | 1 bit |
| Ole Object | Can store pictures, audio, video, or other BLOBs (Binary Large Objects) | up to 1GB |
| Hyperlink | Contain links to other files, including web pages | |
| Lookup Wizard | Let you type a list of options, which can then be chosen from a drop-down list | 4 bytes |