Level Up Your Data Skills: 15 Key Advanced SQL Commands for Beginners

Are you looking to enhance your SQL skills and tackle more complex data challenges? While basic SQL commands are a great start, learning some advanced commands can significantly boost your data manipulation and analysis capabilities. Here are 15 essential advanced SQL commands that can help beginners step up their SQL game.

1. INNER JOIN

INNER JOIN returns records that have matching values in both tables. It's useful for combining related data.

Code:

SELECT columns FROM table1 INNER JOIN table2 ON table1.common_column = table2.common_column;        

2. LEFT JOIN (or LEFT OUTER JOIN)

LEFT JOIN returns all records from the left table and the matched records from the right table. If there's no match, the result is NULL from the right side.

Code:

SELECT columns FROM table1 LEFT JOIN table2 ON table1.common_column = table2.common_column;        

3. RIGHT JOIN (or RIGHT OUTER JOIN)

RIGHT JOIN returns all records from the right table and the matched records from the left table. If there's no match, the result is NULL from the left side.

Code:

SELECT columns FROM table1 RIGHT JOIN table2 ON table1.common_column = table2.common_column;        

4. FULL OUTER JOIN

FULL OUTER JOIN returns all records when there is a match in either left (table1) or right (table2) table records.

Code:

SELECT columns FROM table1 FULL OUTER JOIN table2 ON table1.common_column = table2.common_column;        

5. UNION and UNION ALL

UNION combines the result set of two or more SELECT statements (only distinct values). UNION ALL allows duplicates.

Code:

SELECT column1 FROM table1 UNION SELECT column1 FROM table2;

SELECT column1 FROM table1 UNION ALL SELECT column1 FROM table2;        

6. SUBQUERY (or NESTED QUERY)

A subquery is a query within another query, used to perform more complex operations.

Code:

SELECT column FROM table WHERE column IN (SELECT column FROM table WHERE condition);        

7. EXISTS

EXISTS tests for the existence of any record in a subquery, returning true or false.

Code:

SELECT column FROM table WHERE EXISTS (SELECT column FROM table WHERE condition);        

8. CASE STATEMENT

CASE statement allows you to execute conditional logic in SQL queries.

Code:

SELECT column,
CASE
    WHEN condition1 THEN result1
    WHEN condition2 THEN result2
    ELSE result

END
FROM table;        

9. COMMON TABLE EXPRESSIONS (CTEs)

CTEs are temporary result sets that can be referenced within a SELECT, INSERT, UPDATE, or DELETE statement.

Code:

WITH CTE AS (
        SELECT columns FROM table WHERE condition
)

SELECT columns FROM CTE WHERE condition;        

10. WINDOW FUNCTIONS

Window functions perform calculations across a set of table rows related to the current row.

Code:

SELECT column,
ROW_NUMBER() OVER (PARTITION BY column ORDER BY column) as row_num
FROM table;        

11. PIVOT and UNPIVOT

PIVOT rotates a table-valued expression by turning the unique values from one column into multiple columns. UNPIVOT does the reverse.

Code:

SELECT * FROM
(SELECT column1, column2 FROM table)
PIVOT (SUM(column2) FOR column1 IN (value1, value2));

SELECT * FROM
(SELECT column1, column2, column3 FROM table)
UNPIVOT (column1 FOR column2 IN (column3));        

12. COALESCE

COALESCE returns the first non-null value in a list, useful for handling NULL values.

Code:

SELECT COALESCE(column1, column2, 'default_value') FROM table;        

13. IF-NULL and IS-NULL

These functions replace NULL with a specified replacement value.

Code:

SELECT IFNULL(column, 'replacement') FROM table;
SELECT ISNULL(column, 'replacement') FROM table;        

14. GROUP BY and HAVING

GROUP BY groups rows that have the same values into summary rows. HAVING is used to filter groups.

Code:

SELECT column, COUNT(*) FROM table
GROUP BY column
HAVING COUNT(*) > 1;        

15. TRANSACTIONS

Transactions are used to ensure a series of SQL operations are executed as a unit.

Code:

BEGIN;
UPDATE table SET column = value WHERE condition;
INSERT INTO table (column) VALUES (value);
COMMIT;

ROLLBACK; -- To undo changes        

By incorporating these advanced SQL commands into your repertoire, you'll be well on your way to becoming a more effective and efficient data professional. Keep practicing, and don't hesitate to explore further!

If you found this article helpful, please share your thoughts and experiences with these SQL commands. Let’s connect and grow together in our data journey!