Ashish Yadav
SQL (Structured Query Language) is a programming language used to manage and manipulate data stored in relational databases. Here are 15+ advanced SQL concepts that are commonly used in data science & data analysis:
No.1 JOIN
A JOIN is a way to combine rows from two or more tables based on a related column between them. There are several types of JOINs: INNER JOIN, OUTER JOIN (LEFT JOIN, RIGHT JOIN, and FULL JOIN), and CROSS JOIN. Here is the complete JOIN Tutorial:
Example:
SELECT column_1, column_2
FROM table_1
INNER JOIN table_2
ON table_1.column_name = table_2.column_name;
SELECT column_1, column_2
FROM table_1
LEFT JOIN table_2
ON table_1.column_name = table_2.column_name;
SELECT column_1, column_2
FROM table_1
RIGHT JOIN table_2
ON table_1.column_name = table_2.column_name;
SELECT column_1, column_2
FROM table_1
FULL JOIN table_2
ON table_1.columnNo.2 Indexes
Indexes are data structures that can be created on a table to improve the performance of SELECT, INSERT, UPDATE, and DELETE statements. Indexes work by creating a separate data structure that stores the values from one or more columns in a table, along with a reference to the rows in which those values appear. When a query is executed, the database engine can use the index to quickly locate the rows that match the query’s WHERE clause, rather than having to scan the entire table.
No.3 Stored procedures
A stored procedure is a pre-compiled set of SQL statements that can be executed by calling its name. Stored procedures can accept input parameters and return output parameters. They can be used to encapsulate complex logic, perform operations that would be difficult or inefficient to express in a single SQL statement, or enforce business rules.
No.4 Triggers
A trigger is a special type of stored procedure that is automatically executed by the database engine in response to certain events, such as the insertion or update of a row in a table. Triggers can be used to enforce data integrity, perform auditing, or implement complex business logic.
No.5 Cursors
A cursor is a database object that allows the traversal of a result set one row at a time. Cursors can be used to perform operations on each row of a result set, such as updating or deleting rows or processing the result set in a procedural manner.
No.6 Views
A view is a virtual table that is created based on a SELECT statement. A view does not store data itself, but rather displays data from the underlying tables. Views can be used to simplify complex queries, enforce security by limiting access to certain columns or rows, or present the data in a different way than it is stored in the tables.
No.7 Partitioning
Partitioning is a database optimization technique that involves dividing a large table into smaller, more manageable pieces called partitions. Partitions can be created based on values in one or more columns, such as date ranges or geographical regions. Partitioning can improve the performance of certain types of queries and make it easier to manage and maintain large tables.
No.8 Materialized views
A materialized view is a pre-calculated SELECT statement that is stored in the database as a physical table. Materialized views can be used to improve the performance of queries that involve expensive calculations, by allowing the results of the calculations to be stored and retrieved directly rather than being recalculated each time the query is run.
No.9 Window functions
Window functions are a type of SQL function that performs calculations across a set of rows that are related to the current row. Window functions are often used in conjunction with the OVER() clause to perform calculations such as ranking, running totals, or moving averages.
No.10 CTE (Common Table Expression)
A CTE is a named temporary result set that you can reference within a SELECT, INSERT, UPDATE, DELETE, or CREATE VIEW statement. It can be used to replace a view in a SELECT, INSERT, UPDATE, or DELETE statement.
Example:
WITH cte_name AS (
SELECT column_name
FROM table_name
WHERE condition
)
SELECT * FROM cte_name;No.11 Recursive queries
A recursive query is a type of SELECT statement that can reference itself in the FROM clause. Recursive queries are used to perform operations on hierarchical or tree-structured data, such as traversing a graph or generating a bill of materials.
No.12 Pivot and Unpivot
These are SQL commands that allow you to transform data from rows to columns, or vice versa. They are often used to convert data from a long format to a wide format or to transpose data for easier analysis.
No.13 TCL (Transaction Control Language)
TCL statements are used to manage the transactions in a database. Some examples of TCL statements include COMMIT, ROLLBACK, and SAVEPOINT.
Example:
BEGIN TRANSACTION;
SELECT column_name
FROM table_name
WHERE condition;
COMMIT;
ROLLBACK;
SAVEPOINT savepoint_name;
ROLLBACK TO SAVEPOINT savepoint_name;No.14 Subqueries
A subquery is a SELECT statement that is nested within another SELECT, INSERT, UPDATE, or DELETE statement, or within a set function such as AVG().
Example:
SELECT column_name
FROM table_name
WHERE column_name IN (SELECT column_name FROM table_name WHERE condition);No.15 DML (Data Modification Language)
DML statements are used to modify the data in a database. The three main DML statements are INSERT, UPDATE, and DELETE.
Example:
INSERT INTO table_name (column_1, column_2, ...)
VALUES (value_1, value_2, ...);
UPDATE table_name
SET column_1 = value_1, column_2 = value_2, ...
WHERE condition;
DELETE FROM table_name
WHERE condition;No.16 DDL (Data Definition Language)
DDL statements are used to define the database structure or schema. Some examples of DDL statements include CREATE, ALTER, and DROP.
Example:
CREATE TABLE table_name (
column_1 datatype,
column_2 datatype,
);
ALTER TABLE table_name
ADD column_name datatype;
DROP TABLE table_name;Conclusion:
In this blog, We have covered SQL advanced concepts that you must know to become a data analyst or data scientist.
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