Data Types in SQL

Data types in SQL define the type of data that can be stored in a column or variable. They ensure data integrity by enforcing constraints on the kind of values that can be inserted into a table.

Key Points

Purpose:
- Defines the format and limitations of data in a database.
- Helps in optimizing storage and retrieval of data.
Categories:
SQL data types are broadly classified into the following categories:
- Numeric Types: For numbers.
- String (Character) Types: For text data.
- Date/Time Types: For dates and times.
- Binary Types: For binary data like images or files.
- Special Types: For specific database systems (e.g., JSON, XML).
Variations Across Databases:
While SQL has standard data types, the implementation may vary between databases like MySQL, PostgreSQL, SQL Server, etc.

Categories of SQL Data Types

1. Numeric Data Types

Used for storing numbers.

Type	Description	Example
`INT`	Integer (whole number)	`10`, `-20`
`BIGINT`	Large integer	`9223372036854775807`
`SMALLINT`	Small integer	`32767`
`DECIMAL(p, s)`	Fixed-point number with precision	`DECIMAL(10, 2)` → `123.45`
`NUMERIC(p, s)`	Synonym for `DECIMAL`	`NUMERIC(5, 3)` → `12.345`
`FLOAT`	Approximate floating-point number	`3.14`, `-0.001`
`REAL`	Single-precision floating-point	`2.718`
`BIT`	Binary (0 or 1)	`0`, `1`

2. String (Character) Data Types

Used for text or character data.

Type	Description	Example
`CHAR(n)`	Fixed-length string	`CHAR(5)` → `'abc '`
`VARCHAR(n)`	Variable-length string	`VARCHAR(10)` → `'hello'`
`TEXT`	Large variable-length string	`'This is a long text.'`
`NCHAR(n)`	Fixed-length Unicode string	`NCHAR(5)` → `'abcd '`
`NVARCHAR(n)`	Variable-length Unicode string	`NVARCHAR(10)` → `'world'`
`CLOB`	Character large object	`'Large text data'`

3. Date and Time Data Types

Used for storing date, time, and timestamp values.

Type	Description	Example
`DATE`	Date (YYYY-MM-DD)	`2024-12-21`
`TIME`	Time (HH:MI:SS)	`13:45:30`
`TIMESTAMP`	Date and time	`2024-12-21 13:45:30`
`DATETIME`	Synonym for `TIMESTAMP` in some DBs	`2024-12-21 13:45:30`
`INTERVAL`	Time interval	`INTERVAL '5 DAYS'`

4. Binary Data Types

Used for storing binary data like images or files.

Type	Description	Example
`BINARY(n)`	Fixed-length binary data	`BINARY(5)`
`VARBINARY(n)`	Variable-length binary data	`VARBINARY(10)`
`BLOB`	Binary large object	Binary image data

5. Special Data Types

Used for non-standard data or database-specific needs.

Type	Description	Example
`JSON`	JSON-formatted data	`'{"key": "value"}'`
`XML`	XML-formatted data	`<tag>value</tag>`
`ENUM`	Enumerated list of values	`'small', 'medium', 'large'`
`GEOMETRY`	Spatial data	`POINT(10 20)`

Choosing the Right Data Type

Use the smallest data type that can accommodate your data to optimize storage.
Use CHAR for fixed-length data and VARCHAR for variable-length data.
Use DECIMAL or NUMERIC for precise calculations like monetary data.
Use binary types for storing media or file data.