Here are some essential SQL tips for beginners ๐๐
โ Primary Key = Unique Key + Not Null constraint
โ To perform case insensitive search use UPPER() function ex. UPPER(customer_name) LIKE โA%Aโ
โ LIKE operator is for string data type
โ COUNT(*), COUNT(1), COUNT(0) all are same
โ All aggregate functions ignore the NULL values
โ Aggregate functions MIN, MAX, SUM, AVG, COUNT are for int data type whereas STRING_AGG is for string data type
โ For row level filtration use WHERE and aggregate level filtration use HAVING
โ UNION ALL will include duplicates where as UNION excludes duplicates
โ If the results will not have any duplicates, use UNION ALL instead of UNION
โ We have to alias the subquery if we are using the columns in the outer select query
โ Subqueries can be used as output with NOT IN condition.
โ CTEs look better than subqueries. Performance wise both are same.
โ When joining two tables , if one table has only one value then we can use 1=1 as a condition to join the tables. This will be considered as CROSS JOIN.
โ Window functions work at ROW level.
โ The difference between RANK() and DENSE_RANK() is that RANK() skips the rank if the values are the same.
โ EXISTS works on true/false conditions. If the query returns at least one value, the condition is TRUE. All the records corresponding to the conditions are returned.
Like for more ๐๐
โ Primary Key = Unique Key + Not Null constraint
โ To perform case insensitive search use UPPER() function ex. UPPER(customer_name) LIKE โA%Aโ
โ LIKE operator is for string data type
โ COUNT(*), COUNT(1), COUNT(0) all are same
โ All aggregate functions ignore the NULL values
โ Aggregate functions MIN, MAX, SUM, AVG, COUNT are for int data type whereas STRING_AGG is for string data type
โ For row level filtration use WHERE and aggregate level filtration use HAVING
โ UNION ALL will include duplicates where as UNION excludes duplicates
โ If the results will not have any duplicates, use UNION ALL instead of UNION
โ We have to alias the subquery if we are using the columns in the outer select query
โ Subqueries can be used as output with NOT IN condition.
โ CTEs look better than subqueries. Performance wise both are same.
โ When joining two tables , if one table has only one value then we can use 1=1 as a condition to join the tables. This will be considered as CROSS JOIN.
โ Window functions work at ROW level.
โ The difference between RANK() and DENSE_RANK() is that RANK() skips the rank if the values are the same.
โ EXISTS works on true/false conditions. If the query returns at least one value, the condition is TRUE. All the records corresponding to the conditions are returned.
Like for more ๐๐
๐31โค9๐1
Top 10 Websites to Practice SQL Skills ๐๐
https://www.instagram.com/reel/C5csFy9N5v6/?igsh=eGEwbjRnMWwyejNo
https://www.instagram.com/reel/C5csFy9N5v6/?igsh=eGEwbjRnMWwyejNo
โค2
SQL CHEAT SHEET๐ฉโ๐ป
Here is a quick cheat sheet of some of the most essential SQL commands:
SELECT - Retrieves data from a database
UPDATE - Updates existing data in a database
DELETE - Removes data from a database
INSERT - Adds data to a database
CREATE - Creates an object such as a database or table
ALTER - Modifies an existing object in a database
DROP -Deletes an entire table or database
ORDER BY - Sorts the selected data in an ascending or descending order
WHERE โ Condition used to filter a specific set of records from the database
GROUP BY - Groups a set of data by a common parameter
HAVING - Allows the use of aggregate functions within the query
JOIN - Joins two or more tables together to retrieve data
INDEX - Creates an index on a table, to speed up search times.
Here is a quick cheat sheet of some of the most essential SQL commands:
SELECT - Retrieves data from a database
UPDATE - Updates existing data in a database
DELETE - Removes data from a database
INSERT - Adds data to a database
CREATE - Creates an object such as a database or table
ALTER - Modifies an existing object in a database
DROP -Deletes an entire table or database
ORDER BY - Sorts the selected data in an ascending or descending order
WHERE โ Condition used to filter a specific set of records from the database
GROUP BY - Groups a set of data by a common parameter
HAVING - Allows the use of aggregate functions within the query
JOIN - Joins two or more tables together to retrieve data
INDEX - Creates an index on a table, to speed up search times.
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30 commonly asked questions in database management system (DBMS) interviews
๐๐
1. What is a DBMS?
2. Differentiate between DBMS and RDBMS.
3. What are the advantages and disadvantages of using a DBMS?
4. Explain the three levels of data abstraction in DBMS.
5. What is a database schema?
6. Define normalization and its importance in database design.
7. What are the different types of database models?
8. What is ACID (Atomicity, Consistency, Isolation, Durability) in DBMS?
9. What is a primary key, and why is it important?
10. Explain the concept of foreign keys.
11. Differentiate between a candidate key, primary key, and super key.
12. What is a transaction in a database?
13. Describe the differences between DELETE, TRUNCATE, and DROP commands.
14. What is a view in a database?
15. Explain indexing in databases.
16. What is a stored procedure?
17. What are the advantages of using stored procedures?
18. Describe the differences between clustered and non-clustered indexes.
19. What is a deadlock in DBMS?
20. How can you avoid deadlocks in a database?
21. What is data redundancy, and how can it be minimized?
22. What is a trigger in a database?
23. Describe the different types of joins in SQL.
24. What is a constraint in a database?
25. Explain the differences between a unique key and a primary key.
26. How does SQL differ from NoSQL databases?
27. What is the CAP theorem, and how does it relate to databases?
28. Explain the concept of data warehousing.
29. What are OLTP and OLAP, and how do they differ?
30. How would you approach database performance tuning and optimization?
๐๐
1. What is a DBMS?
2. Differentiate between DBMS and RDBMS.
3. What are the advantages and disadvantages of using a DBMS?
4. Explain the three levels of data abstraction in DBMS.
5. What is a database schema?
6. Define normalization and its importance in database design.
7. What are the different types of database models?
8. What is ACID (Atomicity, Consistency, Isolation, Durability) in DBMS?
9. What is a primary key, and why is it important?
10. Explain the concept of foreign keys.
11. Differentiate between a candidate key, primary key, and super key.
12. What is a transaction in a database?
13. Describe the differences between DELETE, TRUNCATE, and DROP commands.
14. What is a view in a database?
15. Explain indexing in databases.
16. What is a stored procedure?
17. What are the advantages of using stored procedures?
18. Describe the differences between clustered and non-clustered indexes.
19. What is a deadlock in DBMS?
20. How can you avoid deadlocks in a database?
21. What is data redundancy, and how can it be minimized?
22. What is a trigger in a database?
23. Describe the different types of joins in SQL.
24. What is a constraint in a database?
25. Explain the differences between a unique key and a primary key.
26. How does SQL differ from NoSQL databases?
27. What is the CAP theorem, and how does it relate to databases?
28. Explain the concept of data warehousing.
29. What are OLTP and OLAP, and how do they differ?
30. How would you approach database performance tuning and optimization?
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Database keys
Database keys are essential for organizing and managing data effectively. In this post, we'll explore ten key concepts that every IT professional should know.
1. ๐ ๐ฃ๐ฟ๐ถ๐บ๐ฎ๐ฟ๐ ๐๐ฒ๐
- A unique identifier for each record in a table.
- Cannot be null.
- Ensures that each row is unique.
2. ๐ ๐๐ผ๐ฟ๐ฒ๐ถ๐ด๐ป ๐๐ฒ๐
- A field in one table that refers to the Primary Key of another table.
- Establishes relationships between tables.
3. ๐งฉ ๐๐ผ๐บ๐ฝ๐ผ๐๐ถ๐๐ฒ ๐๐ฒ๐
- A combination of two or more columns that uniquely identifies each record.
- Useful when a single column can't uniquely identify a record.
4. ๐ช ๐ฆ๐๐ฝ๐ฒ๐ฟ ๐๐ฒ๐
- One or more columns that can uniquely identify a record.
- A Primary Key is a type of Super Key.
5. ๐ ๐๐ฎ๐ป๐ฑ๐ถ๐ฑ๐ฎ๐๐ฒ ๐๐ฒ๐
- A column or set of columns that could be the Primary Key.
- Must be unique.
6. ๐ ๐จ๐ป๐ถ๐พ๐๐ฒ ๐๐ฒ๐
- Ensures uniqueness for a column or column combination.
- Similar to Primary Key but allows one null value.
7. ๐ค ๐๐น๐๐ฒ๐ฟ๐ป๐ฎ๐๐ฒ ๐๐ฒ๐
- A Candidate Key that isn't the Primary Key.
- Another option for a unique identifier.
8. ๐ ๐ก๐ฎ๐๐๐ฟ๐ฎ๐น ๐๐ฒ๐
- A key that's a natural part of the data, like an email address.
9. ๐ญ ๐ฆ๐๐ฟ๐ฟ๐ผ๐ด๐ฎ๐๐ฒ ๐๐ฒ๐
- An artificial key created when no natural unique identifier exists.
10. ๐ ๐ฆ๐ฒ๐ฐ๐ผ๐ป๐ฑ๐ฎ๐ฟ๐ ๐๐ฒ๐
- Used for data retrieval, not identification.
- Helps create non-clustered indexes.
Database keys are essential for organizing and managing data effectively. In this post, we'll explore ten key concepts that every IT professional should know.
1. ๐ ๐ฃ๐ฟ๐ถ๐บ๐ฎ๐ฟ๐ ๐๐ฒ๐
- A unique identifier for each record in a table.
- Cannot be null.
- Ensures that each row is unique.
2. ๐ ๐๐ผ๐ฟ๐ฒ๐ถ๐ด๐ป ๐๐ฒ๐
- A field in one table that refers to the Primary Key of another table.
- Establishes relationships between tables.
3. ๐งฉ ๐๐ผ๐บ๐ฝ๐ผ๐๐ถ๐๐ฒ ๐๐ฒ๐
- A combination of two or more columns that uniquely identifies each record.
- Useful when a single column can't uniquely identify a record.
4. ๐ช ๐ฆ๐๐ฝ๐ฒ๐ฟ ๐๐ฒ๐
- One or more columns that can uniquely identify a record.
- A Primary Key is a type of Super Key.
5. ๐ ๐๐ฎ๐ป๐ฑ๐ถ๐ฑ๐ฎ๐๐ฒ ๐๐ฒ๐
- A column or set of columns that could be the Primary Key.
- Must be unique.
6. ๐ ๐จ๐ป๐ถ๐พ๐๐ฒ ๐๐ฒ๐
- Ensures uniqueness for a column or column combination.
- Similar to Primary Key but allows one null value.
7. ๐ค ๐๐น๐๐ฒ๐ฟ๐ป๐ฎ๐๐ฒ ๐๐ฒ๐
- A Candidate Key that isn't the Primary Key.
- Another option for a unique identifier.
8. ๐ ๐ก๐ฎ๐๐๐ฟ๐ฎ๐น ๐๐ฒ๐
- A key that's a natural part of the data, like an email address.
9. ๐ญ ๐ฆ๐๐ฟ๐ฟ๐ผ๐ด๐ฎ๐๐ฒ ๐๐ฒ๐
- An artificial key created when no natural unique identifier exists.
10. ๐ ๐ฆ๐ฒ๐ฐ๐ผ๐ป๐ฑ๐ฎ๐ฟ๐ ๐๐ฒ๐
- Used for data retrieval, not identification.
- Helps create non-clustered indexes.
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Top 20 SQL Interview Questions
๐๐
https://www.linkedin.com/posts/sql-analysts_here-is-the-list-of-top-20-sql-interview-activity-7188152088822988800-nuUU?utm_source=share&utm_medium=member_android
๐๐
https://www.linkedin.com/posts/sql-analysts_here-is-the-list-of-top-20-sql-interview-activity-7188152088822988800-nuUU?utm_source=share&utm_medium=member_android
โค8
Basics of SQL ๐๐
1. SQL (Structured Query Language) is a standard programming language used for managing and manipulating relational databases.
2. SQL operates through simple, declarative statements. These statements are used to perform tasks such as querying data, updating data, inserting data, and deleting data from a database.
3. The basic SQL commands include SELECT, INSERT, UPDATE, DELETE, CREATE, and DROP.
4. The SELECT statement is used to retrieve data from a database. It allows you to specify the columns you want to retrieve and filter the results using conditions.
5. The INSERT statement is used to add new records to a table in a database.
6. The UPDATE statement is used to modify existing records in a table.
7. The DELETE statement is used to remove records from a table.
8. The CREATE statement is used to create new tables, indexes, or views in a database.
9. The DROP statement is used to remove tables, indexes, or views from a database.
10. SQL also supports various operators such as AND, OR, NOT, LIKE, IN, BETWEEN, and ORDER BY for filtering and sorting data.
11. SQL also allows for the use of functions and aggregate functions like SUM, AVG, COUNT, MIN, and MAX to perform calculations on data.
12. SQL statements are case-insensitive but conventionally written in uppercase for readability.
13. SQL databases are relational databases that store data in tables with rows and columns. Tables can be related to each other through primary and foreign keys.
14. SQL databases use transactions to ensure data integrity and consistency. Transactions can be committed (saved) or rolled back (undone) based on the success of the operations.
15. SQL databases support indexing for faster data retrieval and performance optimization.
16. SQL databases can be queried using tools like MySQL, PostgreSQL, Oracle Database, SQL Server, SQLite, and others.
Like if you need more similar content
Hope it helps :)
1. SQL (Structured Query Language) is a standard programming language used for managing and manipulating relational databases.
2. SQL operates through simple, declarative statements. These statements are used to perform tasks such as querying data, updating data, inserting data, and deleting data from a database.
3. The basic SQL commands include SELECT, INSERT, UPDATE, DELETE, CREATE, and DROP.
4. The SELECT statement is used to retrieve data from a database. It allows you to specify the columns you want to retrieve and filter the results using conditions.
5. The INSERT statement is used to add new records to a table in a database.
6. The UPDATE statement is used to modify existing records in a table.
7. The DELETE statement is used to remove records from a table.
8. The CREATE statement is used to create new tables, indexes, or views in a database.
9. The DROP statement is used to remove tables, indexes, or views from a database.
10. SQL also supports various operators such as AND, OR, NOT, LIKE, IN, BETWEEN, and ORDER BY for filtering and sorting data.
11. SQL also allows for the use of functions and aggregate functions like SUM, AVG, COUNT, MIN, and MAX to perform calculations on data.
12. SQL statements are case-insensitive but conventionally written in uppercase for readability.
13. SQL databases are relational databases that store data in tables with rows and columns. Tables can be related to each other through primary and foreign keys.
14. SQL databases use transactions to ensure data integrity and consistency. Transactions can be committed (saved) or rolled back (undone) based on the success of the operations.
15. SQL databases support indexing for faster data retrieval and performance optimization.
16. SQL databases can be queried using tools like MySQL, PostgreSQL, Oracle Database, SQL Server, SQLite, and others.
Like if you need more similar content
Hope it helps :)
โค31๐20๐คฃ1
If you are trying to transition into the data analytics domain and getting started with SQL, focus on the most useful concept that will help you solve the majority of the problems, and then try to learn the rest of the topics:
๐๐ป Basic Aggregation function:
1๏ธโฃ AVG
2๏ธโฃ COUNT
3๏ธโฃ SUM
4๏ธโฃ MIN
5๏ธโฃ MAX
๐๐ป JOINS
1๏ธโฃ Left
2๏ธโฃ Inner
3๏ธโฃ Self (Important, Practice questions on self join)
๐๐ป Windows Function (Important)
1๏ธโฃ Learn how partitioning works
2๏ธโฃ Learn the different use cases where Ranking/Numbering Functions are used? ( ROW_NUMBER,RANK, DENSE_RANK, NTILE)
3๏ธโฃ Use Cases of LEAD & LAG functions
4๏ธโฃ Use cases of Aggregate window functions
๐๐ป GROUP BY
๐๐ป WHERE vs HAVING
๐๐ป CASE STATEMENT
๐๐ป UNION vs Union ALL
๐๐ป LOGICAL OPERATORS
Other Commonly used functions:
๐๐ป IFNULL
๐๐ป COALESCE
๐๐ป ROUND
๐๐ป Working with Date Functions
1๏ธโฃ EXTRACTING YEAR/MONTH/WEEK/DAY
2๏ธโฃ Calculating date differences
๐๐ปCTE
๐๐ปViews & Triggers (optional)
Here is an amazing resources to learn & practice SQL: https://bit.ly/3FxxKPz
Share with credits: https://t.me/sqlspecialist
Hope it helps :)
๐๐ป Basic Aggregation function:
1๏ธโฃ AVG
2๏ธโฃ COUNT
3๏ธโฃ SUM
4๏ธโฃ MIN
5๏ธโฃ MAX
๐๐ป JOINS
1๏ธโฃ Left
2๏ธโฃ Inner
3๏ธโฃ Self (Important, Practice questions on self join)
๐๐ป Windows Function (Important)
1๏ธโฃ Learn how partitioning works
2๏ธโฃ Learn the different use cases where Ranking/Numbering Functions are used? ( ROW_NUMBER,RANK, DENSE_RANK, NTILE)
3๏ธโฃ Use Cases of LEAD & LAG functions
4๏ธโฃ Use cases of Aggregate window functions
๐๐ป GROUP BY
๐๐ป WHERE vs HAVING
๐๐ป CASE STATEMENT
๐๐ป UNION vs Union ALL
๐๐ป LOGICAL OPERATORS
Other Commonly used functions:
๐๐ป IFNULL
๐๐ป COALESCE
๐๐ป ROUND
๐๐ป Working with Date Functions
1๏ธโฃ EXTRACTING YEAR/MONTH/WEEK/DAY
2๏ธโฃ Calculating date differences
๐๐ปCTE
๐๐ปViews & Triggers (optional)
Here is an amazing resources to learn & practice SQL: https://bit.ly/3FxxKPz
Share with credits: https://t.me/sqlspecialist
Hope it helps :)
๐26โค1
๐๐A beginner's roadmap for learning SQL:
๐นUnderstand Basics:
Learn what SQL is and its purpose in managing relational databases.
Understand basic database concepts like tables, rows, columns, and relationships.
๐นLearn SQL Syntax:
Familiarize yourself with SQL syntax for common commands like SELECT, INSERT, UPDATE, DELETE.
Understand clauses like WHERE, ORDER BY, GROUP BY, and JOIN.
๐นSetup a Database:
Install a relational database management system (RDBMS) like MySQL, SQLite, or PostgreSQL.
Practice creating databases, tables, and inserting data.
๐นRetrieve Data (SELECT):
Learn to retrieve data from a database using SELECT statements.
Practice filtering data using WHERE clause and sorting using ORDER BY.
๐นModify Data (INSERT, UPDATE, DELETE):
Understand how to insert new records, update existing ones, and delete data.
Be cautious with DELETE to avoid unintentional data loss.
๐นWorking with Functions:
Explore SQL functions like COUNT, AVG, SUM, MAX, MIN for data analysis.
Understand string functions, date functions, and mathematical functions.
๐นData Filtering and Sorting:
Learn advanced filtering techniques using AND, OR, and IN operators.
Practice sorting data using multiple columns.
๐นTable Relationships (JOIN):
Understand the concept of joining tables to retrieve data from multiple tables.
Learn about INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
๐นGrouping and Aggregation:
Explore GROUP BY clause to group data based on specific columns.
Understand aggregate functions for summarizing data (SUM, AVG, COUNT).
๐นSubqueries:
Learn to use subqueries to perform complex queries.
Understand how to use subqueries in SELECT, WHERE, and FROM clauses.
๐นIndexes and Optimization:
Gain knowledge about indexes and their role in optimizing queries.
Understand how to optimize SQL queries for better performance.
๐นTransactions and ACID Properties:
Learn about transactions and the ACID properties (Atomicity, Consistency, Isolation, Durability).
Understand how to use transactions to maintain data integrity.
๐นNormalization:
Understand the basics of database normalization to design efficient databases.
Learn about 1NF, 2NF, 3NF, and BCNF.
๐นBackup and Recovery:
Understand the importance of database backups.
Learn how to perform backups and recovery operations.
๐นPractice and Projects:
Apply your knowledge through hands-on projects.
Practice on platforms like LeetCode, HackerRank, or build your own small database-driven projects.
๐๐Remember to practice regularly and build real-world projects to reinforce your learning. Happy coding!
๐นUnderstand Basics:
Learn what SQL is and its purpose in managing relational databases.
Understand basic database concepts like tables, rows, columns, and relationships.
๐นLearn SQL Syntax:
Familiarize yourself with SQL syntax for common commands like SELECT, INSERT, UPDATE, DELETE.
Understand clauses like WHERE, ORDER BY, GROUP BY, and JOIN.
๐นSetup a Database:
Install a relational database management system (RDBMS) like MySQL, SQLite, or PostgreSQL.
Practice creating databases, tables, and inserting data.
๐นRetrieve Data (SELECT):
Learn to retrieve data from a database using SELECT statements.
Practice filtering data using WHERE clause and sorting using ORDER BY.
๐นModify Data (INSERT, UPDATE, DELETE):
Understand how to insert new records, update existing ones, and delete data.
Be cautious with DELETE to avoid unintentional data loss.
๐นWorking with Functions:
Explore SQL functions like COUNT, AVG, SUM, MAX, MIN for data analysis.
Understand string functions, date functions, and mathematical functions.
๐นData Filtering and Sorting:
Learn advanced filtering techniques using AND, OR, and IN operators.
Practice sorting data using multiple columns.
๐นTable Relationships (JOIN):
Understand the concept of joining tables to retrieve data from multiple tables.
Learn about INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
๐นGrouping and Aggregation:
Explore GROUP BY clause to group data based on specific columns.
Understand aggregate functions for summarizing data (SUM, AVG, COUNT).
๐นSubqueries:
Learn to use subqueries to perform complex queries.
Understand how to use subqueries in SELECT, WHERE, and FROM clauses.
๐นIndexes and Optimization:
Gain knowledge about indexes and their role in optimizing queries.
Understand how to optimize SQL queries for better performance.
๐นTransactions and ACID Properties:
Learn about transactions and the ACID properties (Atomicity, Consistency, Isolation, Durability).
Understand how to use transactions to maintain data integrity.
๐นNormalization:
Understand the basics of database normalization to design efficient databases.
Learn about 1NF, 2NF, 3NF, and BCNF.
๐นBackup and Recovery:
Understand the importance of database backups.
Learn how to perform backups and recovery operations.
๐นPractice and Projects:
Apply your knowledge through hands-on projects.
Practice on platforms like LeetCode, HackerRank, or build your own small database-driven projects.
๐๐Remember to practice regularly and build real-world projects to reinforce your learning. Happy coding!
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SQL Zero to Hero
๐๐
https://www.linkedin.com/posts/sql-analysts_many-people-pay-too-much-to-learn-sql-but-activity-7201219129310138368-2U6a
Like for more
๐๐
https://www.linkedin.com/posts/sql-analysts_many-people-pay-too-much-to-learn-sql-but-activity-7201219129310138368-2U6a
Like for more
๐12โค3