Data Types

SQL, or Structured Query Language, is a programming language primarily used for managing and manipulating relational databases. At the heart of these operations are various data types that SQL uses to define the data that can be stored in a particular column in a table.

Standard SQL Data Types

Numeric Data Types

integer: For whole numbers, including both positive and negative values. For example, 123, 456.
float/real: For floating point numbers or numbers with decimal points. For example, 123.45.
decimal/numeric: These are used to store exact numeric values where precision is essential. For example, 123.45.

String Data Types

char(n): Fixed-length character string, where n defines the length. For example, char(5) could hold apple.
varchar(n): Variable-length character string, where n defines the maximum string length. varchar(5) could hold apple or ap.
text: For holding large amounts of text data.

Date and Time Data Types

date: For date values in the format YYYY-MM-DD. For example, 2023-06-03.
time: For time values in the format HH:MI:SS. For example, 14:30:00.
timestamp: For holding date and time values. For example, 2023-06-03 14:30:00.

SQL Data Types in Different Databases

While the above data types are common in most SQL databases, various databases (like MySQL, SQL Server, PostgreSQL, and SQLite) may have additional data types or variations of the standard ones. For example:

MySQL and PostgreSQL support a boolean data type for true/false values, while SQL Server uses bit.
PostgreSQL has uuid for universally unique identifiers.
SQL Server offers money for currency storage.

Importance of Choosing Correct Data Types

Choosing the correct data type is essential for multiple reasons:

Data integrity: By choosing the correct data type, you ensure the data stored in the column adheres to the expected format.
Performance: Using the appropriate data type can reduce a database’s space, improving performance.
Preventing errors: Certain operations are only valid on certain data types.

Examples

Creating a table with different data types:

CREATE TABLE employee (
    id integer,
    first_name varchar(50),
    last_name char(50),
    salary decimal(10, 2),
    birth_date date,
    timestamp_column timestamp
);

Inserting data into the table:

INSERT INTO employee (id, first_name, last_name, salary, birth_date, timestamp_column)
VALUES (1, 'John', 'Doe', 50000.00, '1980-05-01', '2023-06-03 14:30:00');