Introduction to Chapter Structured Query 8 Language (SQL) | Class 11 Informatics Practices Notes

8.3 DATA TYPES AND CONSTRAINTS IN MySQL

A database consists of one or more relations (tables), each made up of attributes (columns). Each attribute has a data type that defines the kind of data it can hold and the operations that can be performed on it. For example, arithmetic operations can be performed on numeric data but not on character data. MySQL supports several data types, mainly categorized as numeric types, date and time types, and string types (character and byte). Commonly used data types include CHAR(n) for fixed-length strings, VARCHAR(n) for variable-length strings, INT for integers, FLOAT for floating-point numbers, and DATE for date values in 'YYYY-MM-DD' format. Constraints are restrictions applied to attribute values to ensure data accuracy and reliability. Common SQL constraints include NOT NULL (disallows NULL values), UNIQUE (ensures all values in a column are distinct), DEFAULT (specifies a default value if none is provided), PRIMARY KEY (uniquely identifies each row), and FOREIGN KEY (references a primary key in another table). Constraints help maintain data integrity but are not mandatory for every attribute. Understanding data types and constraints is essential for designing robust database tables.

📊 Diagram: Figure 8.1: MySQL Shell; Table 8.1 Commonly used data types in MySQL; Table 8.2 Commonly used SQL Constraints

🧪 Activity: Activity 8.2: Explore other data types supported in MySQL and variants of integer and float data types.

🔗 Connection: This section explains data types and constraints, preparing for the next section on SQL commands for data definition.