Database design best practices in SQL - Step-by-Step Execution

Concept Flow - Database design best practices

Identify Data Needs

↓

Define Tables & Columns

↓

Set Primary Keys

↓

Establish Relationships

↓

Normalize Data

↓

Add Indexes

↓

Review & Optimize

↓

Deploy

This flow shows the main steps to design a good database: understand data, create tables, set keys, link tables, organize data, add indexes, then review before using.

Execution Sample

SQL

CREATE TABLE Customers (
  CustomerID INT PRIMARY KEY,
  Name VARCHAR(100),
  Email VARCHAR(100) UNIQUE
);

CREATE TABLE Orders (
  OrderID INT PRIMARY KEY,
  CustomerID INT,
  OrderDate DATE,
  FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID)
);

This code creates two tables, Customers and Orders, linking them with a foreign key to keep data organized and avoid duplicates.

Execution Table

Step	Action	Result	Notes
1	Create Customers table	Table Customers created with CustomerID as primary key	Primary key ensures unique customers
2	Add Name and Email columns	Columns added; Email set as UNIQUE	Unique email avoids duplicates
3	Create Orders table	Table Orders created with OrderID as primary key	Unique order IDs
4	Add CustomerID and OrderDate columns	Columns added	CustomerID links to Customers
5	Set FOREIGN KEY on CustomerID	Foreign key constraint established	Ensures orders link to valid customers
6	Review tables	Tables normalized and ready	Data is organized and consistent
7	Add indexes if needed	Indexes improve query speed	Optional but recommended for large data
8	Deploy database	Database ready for use	Design best practices applied
9	End	No more steps	Design complete

💡 All design steps completed to ensure data integrity and efficiency

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	Final
Customers Table	None	Created with CustomerID PK	Created with CustomerID PK	Created with CustomerID PK and Email UNIQUE	Finalized with all columns and constraints
Orders Table	None	None	Created with OrderID PK	Created with FK to Customers	Finalized with all columns and constraints
Indexes	None	None	None	None	Added if needed for performance

Key Moments - 3 Insights

Why do we set a primary key on a table?

A primary key uniquely identifies each row, preventing duplicates and helping link tables, as shown in execution_table steps 1 and 3.

What is the purpose of a foreign key?

A foreign key links one table to another to keep data consistent, as seen in step 5 where Orders.CustomerID references Customers.CustomerID.

Why do we make some columns UNIQUE?

Making columns UNIQUE, like Email in Customers, prevents duplicate values and keeps data clean, shown in step 2.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the foreign key constraint added?

A Step 5

B Step 2

C Step 3

D Step 7

💡 Hint

Check the 'Action' column for 'Set FOREIGN KEY' in execution_table

According to variable_tracker, what is the state of the Customers table after Step 5?

A Created with CustomerID PK only

B Created with CustomerID PK and Email UNIQUE

C Not created yet

D Created with all columns and constraints

💡 Hint

Look at the 'Customers Table' row under 'After Step 5' in variable_tracker

If we skip adding UNIQUE to Email, what problem might occur?

A Orders would not link to Customers

B Primary keys would be missing

C Emails could be duplicated in Customers

D Tables would not be created

💡 Hint

Refer to key_moments about UNIQUE columns and step 2 in execution_table

Concept Snapshot

Database Design Best Practices:
- Identify data needs clearly
- Define tables with primary keys
- Use foreign keys to link tables
- Normalize data to avoid duplicates
- Add UNIQUE constraints where needed
- Create indexes for faster queries
- Review and optimize before deployment

Full Transcript

This visual execution shows the best practices for designing a database. First, understand what data you need. Then create tables with primary keys to uniquely identify rows. Add columns and set UNIQUE constraints to avoid duplicates. Link tables using foreign keys to keep data consistent. Normalize data to organize it well. Optionally add indexes to speed up queries. Finally, review and deploy the database. The execution table traces each step, and the variable tracker shows how tables and constraints evolve. Key moments clarify why primary keys, foreign keys, and unique constraints matter. The quiz tests understanding of these steps.

Practice

1. Which of the following is a key reason to use primary keys in database tables?

easy

A. To store large amounts of text data

B. To create duplicate records easily

C. To speed up the database server hardware

D. To uniquely identify each record in the table

Solution

1. Step 1: Understand the role of primary keys

   Primary keys uniquely identify each row in a table, preventing duplicates.

2. Step 2: Compare options with primary key purpose

   Only To uniquely identify each record in the table describes uniqueness, which is the main purpose of primary keys.

3. Final Answer:

   To uniquely identify each record in the table -> Option D

4. Quick Check:

   Primary key = unique record ID [OK]

Hint: Primary keys always ensure unique records [OK]

Common Mistakes:

• Thinking primary keys store large text
• Confusing primary keys with performance hardware
• Believing primary keys allow duplicates

2. Which SQL statement correctly creates a table with a primary key on the id column?

easy

A. CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(50));

B. CREATE TABLE users (id INT, name VARCHAR(50) PRIMARY KEY);

C. CREATE TABLE users (id INT, name VARCHAR(50), PRIMARY id);

D. CREATE TABLE users (id INT UNIQUE, name VARCHAR(50));

Solution

1. Step 1: Review correct primary key syntax

   The primary key is declared as id INT PRIMARY KEY inside the column definition.

2. Step 2: Check each option's syntax

   CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(50)); uses correct syntax; A has invalid syntax; B places PRIMARY KEY on wrong column; D uses UNIQUE but not PRIMARY KEY.

3. Final Answer:

   CREATE TABLE users (id INT PRIMARY KEY, name VARCHAR(50)); -> Option A

4. Quick Check:

   Primary key syntax = column_name TYPE PRIMARY KEY [OK]

Hint: Primary key goes right after the column type [OK]

Common Mistakes:

• Placing PRIMARY KEY on wrong column
• Using UNIQUE instead of PRIMARY KEY
• Incorrect syntax for primary key declaration

3. Given these two tables:
CREATE TABLE authors (author_id INT PRIMARY KEY, name VARCHAR(100));
CREATE TABLE books (book_id INT PRIMARY KEY, title VARCHAR(100), author_id INT, FOREIGN KEY (author_id) REFERENCES authors(author_id));
What will happen if you try to insert a book with author_id = 5, but no author with author_id = 5 exists?

medium

A. The insert will succeed and create a new author automatically

B. The insert will fail due to foreign key constraint violation

C. The insert will succeed but author_id will be set to NULL

D. The insert will succeed but cause duplicate author records

Solution

1. Step 1: Understand foreign key constraints

   Foreign keys require the referenced value to exist in the parent table to maintain data integrity.

2. Step 2: Apply constraint to the insert operation

   Inserting a book with author_id = 5 fails if no author with id 5 exists, causing a constraint violation.

3. Final Answer:

   The insert will fail due to foreign key constraint violation -> Option B

4. Quick Check:

   Foreign key enforces existing parent record [OK]

Hint: Foreign keys block inserts without matching parent [OK]

Common Mistakes:

• Assuming foreign keys auto-create missing parents
• Thinking foreign keys allow NULL by default
• Ignoring constraint errors on insert

4. You have a table orders with columns order_id (primary key), customer_id, and order_date. You want to add a foreign key constraint on customer_id referencing customers(customer_id). Which of these statements has an error?

medium

A. ALTER TABLE orders ADD FOREIGN KEY (customer_id) REFERENCES customers(customer_id);

B. ALTER TABLE orders ADD CONSTRAINT fk_customer FOREIGN KEY (customer_id) REFERENCES customers(customer_id);

C. ALTER TABLE orders ADD FOREIGN KEY customer_id REFERENCES customers(customer_id);

D. ALTER TABLE orders ADD CONSTRAINT fk_customer FOREIGN KEY (customer_id) REFERENCES customers(customer_id) ON DELETE CASCADE;

Solution

1. Step 1: Review correct syntax for adding foreign keys

   The correct syntax requires parentheses around the column name after FOREIGN KEY.

2. Step 2: Identify the incorrect statement

   ALTER TABLE orders ADD FOREIGN KEY customer_id REFERENCES customers(customer_id); misses parentheses around customer_id, causing syntax error.

3. Final Answer:

   ALTER TABLE orders ADD FOREIGN KEY customer_id REFERENCES customers(customer_id); -> Option C

4. Quick Check:

   Foreign key column must be in parentheses [OK]

Hint: Always use parentheses around foreign key columns [OK]

Common Mistakes:

• Omitting parentheses around column names
• Forgetting to name the constraint (optional but recommended)
• Misplacing ON DELETE options

5. You are designing a database for a library. You want to track books, authors, and the categories each book belongs to. Which design best follows database design best practices?

hard

A. Separate tables for books, authors, and categories with primary keys and foreign keys linking them

B. Separate tables for books and categories only, storing author names as text in books

C. One table for books and authors combined, and a separate table for categories

D. One table with columns: book_id, book_title, author_name, category_name

Solution

1. Step 1: Analyze normalization and relationships

   Best practice is to separate entities into tables and link them with keys to avoid duplication.

2. Step 2: Evaluate each option's design

   Separate tables for books, authors, and categories with primary keys and foreign keys linking them uses separate tables with keys, which supports clear organization and data consistency.

3. Final Answer:

   Separate tables for books, authors, and categories with primary keys and foreign keys linking them -> Option A

4. Quick Check:

   Separate tables + keys = best design [OK]

Hint: Use separate tables and keys for related data [OK]

Common Mistakes:

• Putting all data in one table causing duplicates
• Mixing unrelated data in same table
• Storing related entity names as plain text