Day 4: Understanding the MERGE Statement in SQL – Upsert Made Easy! | Techeology nerds

Welcome to Day 4 of our 50 SQL Questions in 50 Days series! 🎉
In this video, we’re diving into the Types of SQL Statements, an essential topic for beginners and a foundational concept for advanced learners.

Day 4: Understanding the MERGE Statement in SQL – Upsert Made Easy! | Techeology nerds
🎯 What You’ll Learn Today:
🔹 What are SQL Statements?
🔹 The 5 Categories of SQL Statements:

DML (Data Manipulation Language)
DDL (Data Definition Language)
DCL (Data Control Language)
TCL (Transaction Control Language)
DRL/SELECT (Data Retrieval Language)
🔹 Practical Examples of Each Type.
🔹 How and When to Use Each Type in Real-World Scenarios.
📚 Quick Summary of SQL Types:
1️⃣ DML (Data Manipulation Language):

Commands: INSERT, UPDATE, DELETE.
Purpose: Modify data within tables.
Example: INSERT INTO employees (id, name) VALUES (1, 'John');
2️⃣ DDL (Data Definition Language):

Commands: CREATE, ALTER, DROP, TRUNCATE.
Purpose: Define or modify database structure.
Example: CREATE TABLE employees (id INT, name VARCHAR(50));
3️⃣ DCL (Data Control Language):

Commands: GRANT, REVOKE.
Purpose: Manage user permissions.
Example: GRANT SELECT ON employees TO user123;
4️⃣ TCL (Transaction Control Language):

Commands: COMMIT, ROLLBACK, SAVEPOINT.
Purpose: Manage database transactions.
Example:
sql
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BEGIN TRANSACTION;
UPDATE employees SET salary = 50000 WHERE id = 1;
COMMIT;
5️⃣ DRL/SELECT (Data Retrieval Language):

Command: SELECT.
Purpose: Retrieve data from the database.
Example: SELECT * FROM employees;
💡 Why This Topic is Important:
Interviews: Frequently asked to differentiate these categories.
Real-World Applications: Knowing when and how to use these commands enhances database efficiency and clarity.
🎬 Watch the video now to explore each type with live examples and practical tips!
📢 Don’t forget to comment your doubts or share your experience with SQL.

📲 Stay Connected:
💻 LinkedIn: Techeology Nerds
📷 Instagram: @Techeology_Nerds

Written & Presented by: Anurag Rajbhar
Edited by: Surya
Thumbnail Design: Surya

✨ Join the Journey: #50SQLIn50Days
#SQLStatements #LearnSQL #TecheologyNerds #Day1SQL

The MERGE statement in SQL is a powerful tool used for performing "upsert" operations, which means updating existing rows or inserting new rows based on certain conditions. It allows combining multiple operations (INSERT, UPDATE, DELETE) into a single SQL query, improving efficiency and maintainability.

Key Concepts of MERGE Statement:
Purpose:
The MERGE statement is used to synchronize two tables by inserting, updating, or deleting data as needed.

Structure:
A typical MERGE statement consists of three parts:

Source Table: The table (or dataset) providing new data.
Target Table: The table where changes (insert/update/delete) will occur.
Condition: The criteria used to determine whether to insert, update, or delete.
Syntax:

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MERGE INTO target_table AS T
USING source_table AS S
ON (T.matching_column = S.matching_column)
WHEN MATCHED THEN
UPDATE SET T.column1 = S.column1, T.column2 = S.column2
WHEN NOT MATCHED THEN
INSERT (column1, column2)
VALUES (S.column1, S.column2);
Key Clauses:

WHEN MATCHED THEN: Defines the action to take (e.g., UPDATE or DELETE) if a match is found.
WHEN NOT MATCHED THEN: Specifies what to do (e.g., INSERT) when no match is found.
Advantages:

Reduces the need for multiple queries (INSERT + UPDATE).
Improves performance by consolidating operations.
Ensures data consistency during synchronization.
Use Case Scenarios:

Data Synchronization: Keeping two tables in sync.
Data Warehousing: Consolidating data from different sources.
Upsert Operations: Adding new records and updating existing ones.
Example: MERGE in Action
Imagine you have two tables:

employees (Target Table) – Contains existing employee records.
new_employees (Source Table) – Contains updates and new hires.
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MERGE INTO employees AS E
USING new_employees AS N
ON (E.employee_id = N.employee_id)
WHEN MATCHED THEN
UPDATE SET
E.salary = N.salary,
E.department = N.department
WHEN NOT MATCHED THEN
INSERT (employee_id, name, salary, department)
VALUES (N.employee_id, N.name, N.salary, N.department);

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