SQL Data Types and Constraints

SQL Data Types:

Data types in SQL specify the kind of data that can be stored in a column of a database table. They define the format, range, and size of the data that a column can hold. SQL provides a wide range of data types, including:

1. Numeric Data Types:
   • INT (integer), BIGINT (large integer), DECIMAL/NUMERIC (fixed-point numbers), FLOAT/REAL (floating-point numbers).
2. Character Data Types:
   • CHAR (fixed-length character strings), VARCHAR (variable-length character strings), TEXT (long text).
3. Date and Time Data Types:
   • DATE (date), TIME (time), DATETIME/TIMESTAMP (date and time), INTERVAL (a time span).
4. Binary Data Types:
   • BINARY (fixed-length binary strings), VARBINARY (variable-length binary strings), BLOB (binary large objects).
5. Boolean Data Type:
   • BOOLEAN or BOOL (represents true or false values).
6. Enumeration Data Type:
   • ENUM (represents a list of predefined values).
7. Other Data Types:
   • JSON (stores JSON data), XML (stores XML data), and more.

Choosing the appropriate data type for each column is crucial for optimizing database performance and ensuring data accuracy. For instance, using an INT for an age column is more efficient than using a VARCHAR, which is typically used for names or textual data.

SQL Constraints: Constraints in SQL are rules and conditions that you apply to database tables to maintain data integrity and enforce business rules. They define the limits and restrictions on what kind of data can be inserted, updated, or deleted in a table. Common SQL constraints include:

1. Primary Key Constraint:
   • Ensures each row in a table has a unique identifier. It’s used to define the primary key for a table.
2. Unique Constraint:
   • Ensures that values in a column (or a combination of columns) are unique across all rows in the table.
3. Check Constraint:
   • Defines a condition that data must meet to be inserted or updated. For example, ensuring ages are positive.
4. Default Constraint:
   • Specifies a default value for a column if no value is provided during an INSERT operation.
5. Foreign Key Constraint:
   • Enforces referential integrity by ensuring that values in a column match values in another table’s primary key.

Constraints help maintain data quality, prevent errors, and ensure that the data conforms to the required standards. They are essential for protecting the integrity and consistency of the database.