Data types in SQL specify the type of data that a particular column or variable can hold in a database table. The most common data types in SQL include integer, float, decimal, char, varchar, text, date, and timestamp. Integers are used to represent whole numbers, while floats and decimals are used to represent decimal numbers with varying degrees of precision. Char and varchar are used to store character strings, with varchar having a variable length, and text being used for larger strings. Date and timestamp are used to store dates and times, respectively.
Data Types in SQL
Data types in SQL are important because they determine the kind of data that can be stored in a column of a table. Each data type has specific characteristics and properties that define the type of data it can store, such as the range of values, precision, and size.
By specifying the appropriate data type for each column, you can ensure that the data stored in the table is accurate and consistent, which is critical for maintaining the integrity of the database. Using the wrong data type can lead to data loss, incorrect results, and poor performance.
Data types are important when working with functions and operators in SQL. Some functions and operators are only compatible with certain data types, so it’s important to choose the appropriate data type to ensure that your queries work as intended.
Data types can impact database performance. For example, using a larger data type than necessary can lead to wasted disk space and slower query performance, while using a smaller data type can lead to data truncation and incorrect results. Selecting the appropriate data type is an important consideration when designing a database in SQL to ensure the accuracy, consistency, and performance of the data stored in the database.
Numeric Data Types
In SQL, numeric data types are used to store numeric values. They can hold integers, floating-point numbers, and decimal values, and they have different ranges and precisions.
Here is a list of common numeric data types in SQL, with examples of the range of values that they can hold:
- INT: Integer number (whole number). Can hold values from -2^31 to 2^31-1. Example: -2147483648 to 2147483647.
- BIGINT: Large integer number. Can hold values from -2^63 to 2^63-1. Example: -9223372036854775808 to 9223372036854775807.
- SMALLINT: Small integer number. Can hold values from -2^15 to 2^15-1. Example: -32768 to 32767.
- TINYINT: Tiny integer number. Can hold values from 0 to 255. Example: 0 to 255.
- FLOAT(size): Floating-point number. Size specifies the number of bits used to store the value. Example: -1.79E+308 to -2.23E-308, 0, and 2.23E-308 to 1.79E+308.
- DOUBLE(size): Double-precision floating-point number. Size specifies the number of bits used to store the value. Example: -1.79E+308 to -2.23E-308, 0, and 2.23E-308 to 1.79E+308.
- DECIMAL(size,d): Exact numeric value. Size specifies the total number of digits, and d specifies the number of digits after the decimal point. Example: -10^38 +1 to 10^38 -1.
String Data Types
String data types are used to store character strings. They can hold letters, numbers, and special characters, and they have different sizes and characteristics.
Here is a list of common string data types in SQL, with examples of the range of values that they can hold:
- CHAR(size): Fixed-length character string. Size specifies the maximum number of characters that can be stored (maximum size is 255). Example: ‘Hello World!’ (length 11).
- VARCHAR(size): Variable-length character string. Size specifies the maximum number of characters that can be stored (maximum size is 65535). Example: ‘Hello World!’ (length 11).
- TEXT: Variable-length character string with a maximum size of 2^31-1 characters. Example: ‘This is a very long string that can hold a large amount of text.’ (length 72).
- NCHAR(size): Fixed-length Unicode character string. Size specifies the maximum number of characters that can be stored (maximum size is 255). Example: ‘你好世界！’ (length 4).
- NVARCHAR(size): Variable-length Unicode character string. Size specifies the maximum number of characters that can be stored (maximum size is 65535). Example: ‘你好世界！’ (length 4).
- NTEXT: Variable-length Unicode character string with a maximum size of 2^30-1 characters. Example: ‘这是一个非常长的字符串，可以容纳大量文本。’ (length 22).
Date and Time Data Types
Date and time data types are used to store date and time values in SQL. They can hold a date, a time, or a combination of both, and they have different precisions and ranges.
Here is a list of common date and time data types in SQL:
- DATE: Date value (year, month, and day). Example: ‘2022-01-01’ (January 1st, 2022).
- TIME: Time value (hour, minute, and second). Example: ’18:30:00′ (6:30 PM).
- DATETIME: Date and time value (year, month, day, hour, minute, and second). Example: ‘2022-01-01 18:30:00’ (January 1st, 2022, 6:30 PM).
- TIMESTAMP: Date and time value with a precision of 1 second. Example: ‘2022-01-01 18:30:00’ (January 1st, 2022, 6:30 PM).
Binary Data Types
Binary data types are used to store binary data, such as images, documents, and audio files in SQL. They can hold a fixed or variable amount of data, and they have different sizes and characteristics.
Here is a list of common binary data types in SQL:
- BINARY(size): Fixed-length binary data. Size specifies the maximum number of bytes that can be stored (maximum size is 8000).
- VARBINARY(size): Variable-length binary data. Size specifies the maximum number of bytes that can be stored (maximum size is 8000).
- IMAGE: Variable-length binary data with a maximum size of 2^31-1 bytes.
- BLOB: Binary Large Object. Variable-length binary data with a maximum size of 2^31-1 bytes.
Misc Data Types
There are a few miscellaneous data types that don’t fit into the categories of numeric, string, date and time, or binary data types in SQL. These data types have specific uses and characteristics.
Here is a list of common miscellaneous data types in SQL:
- BOOLEAN: A true or false value.
- ENUM: A list of predefined values.
- SET: A set of predefined values.
- JSON: A JSON data object.
