Managing Tables in SQL Database Engine

Tables are the fundamental data structures in a relational database. They store data in rows and columns. Effective table management is crucial for database performance, integrity, and maintainability.

Creating Tables

Use the CREATE TABLE statement to define the structure of a new table. You specify the table name, column names, data types for each column, and any constraints.

CREATE TABLE Customers (
    CustomerID INT PRIMARY KEY IDENTITY(1,1),
    FirstName VARCHAR(50) NOT NULL,
    LastName VARCHAR(50) NOT NULL,
    Email VARCHAR(100) UNIQUE,
    RegistrationDate DATE DEFAULT GETDATE()
);
        

Altering Tables

The ALTER TABLE statement allows you to modify an existing table's structure. You can add, delete, or modify columns, as well as add or drop constraints.

Adding a Column

ALTER TABLE Customers
ADD PhoneNumber VARCHAR(20);
        

Modifying a Column

ALTER TABLE Customers
ALTER COLUMN Email VARCHAR(150);
        

Dropping a Column

ALTER TABLE Customers
DROP COLUMN PhoneNumber;
        

Adding a Constraint

ALTER TABLE Orders
ADD CONSTRAINT FK_CustomerOrder
FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID);
        

Dropping Tables

Use the DROP TABLE statement to remove a table and all its data from the database. This action is irreversible.

DROP TABLE Customers;
        

Table Constraints

Constraints enforce data integrity rules:

• PRIMARY KEY: Uniquely identifies each row in a table. Cannot contain NULL values.
• FOREIGN KEY: Enforces referential integrity between two tables. Links a column in one table to a primary key in another.
• UNIQUE: Ensures that all values in a column are different.
• NOT NULL: Ensures that a column cannot have a NULL value.
• CHECK: Ensures that all values in a column satisfy a specific condition.
• DEFAULT: Sets a default value for a column when no value is specified.

Key Table Management Concepts

Data Types

Choosing appropriate data types (e.g., INT, VARCHAR, DATE, DECIMAL) is critical for efficient storage and data accuracy.

Indexing

Indexes improve the speed of data retrieval operations. Consider creating indexes on columns that are frequently used in WHERE clauses or JOIN conditions.

CREATE INDEX IX_CustomerEmail
ON Customers (Email);
                

Normalization

Database normalization is a design process that organizes data to minimize redundancy and improve data integrity. Understanding normal forms (1NF, 2NF, 3NF) is important for good table design.

Common Table Operations