SQL Data Types

In SQL, a data type specifies the type of data that can be stored in a column or variable. The following are some common data types used in SQL:

• INT or INTEGER: integer values (e.g., 1, 2, 3, ...)

• BIGINT: larger integer values (e.g., -9223372036854775808 to 9223372036854775807)

• SMALLINT: smaller integer values (e.g., -32768 to 32767)

• DECIMAL or NUMERIC: fixed-point decimal numbers (e.g., 123.45)

• FLOAT or REAL: floating-point numbers (e.g., 1.23E-10)

• DOUBLE PRECISION: double-precision floating-point numbers (e.g., 1.7976931348623157E+308)

• CHAR or CHARACTER: fixed-length character strings (e.g., 'ABC')

• VARCHAR or VARCHAR2: variable-length character strings (e.g., 'ABC', 'ABCD', 'ABCDE', ...)

• TEXT: large variable-length character strings (e.g., up to 2^31-1 characters)

• DATE: dates (e.g., '2023-02-28')

• TIME: times (e.g., '14:30:00')

• DATETIME or TIMESTAMP: dates and times (e.g., '2023-02-28 14:30:00')

• BOOLEAN or BOOL: true/false values (e.g., TRUE, FALSE)

Some databases may also support additional data types beyond these common ones. When creating a table, you specify the data type for each column. For example, the following SQL statement creates a table called employees with four columns, each with a different data type:

CREATE TABLE employees (
    id INT,
    name VARCHAR(50),
    salary DECIMAL(10,2),
    hire_date DATE
);

In this example, we are creating a table called employees with four columns: id of type INT, name of type VARCHAR(50), salary of type DECIMAL(10,2), and hire_date of type DATE.

Choosing the appropriate data type for each column is important for data integrity, storage efficiency, and query performance. For example, using a DECIMAL data type for currency values ensures that they are stored with the correct precision, and using an appropriate string data type can improve storage efficiency and query performance.