SQL

Mind map for SQL

Introduction to SQL

SQL, which stands for Structured Query Language, is a powerful and standardized language used for managing and manipulating relational databases. It provides a structured approach to interact with databases, allowing users to perform various tasks such as querying data, updating records, creating and modifying database objects, and managing user permissions.

SQL is essential for anyone working with databases, from database administrators and developers to data analysts and business intelligence professionals. It is widely used across industries and plays a crucial role in handling large volumes of data efficiently.

Key Concepts in SQL:

1. DQL (Data Query Language):**
— SELECT: The SELECT statement is used to retrieve data from one or more tables in a database. It allows you to specify which columns you want to retrieve and can include conditions using the WHERE clause to filter the rows returned.
— ORDER BY: ORDER BY is used to sort the result set based on one or more columns. You can specify ascending (ASC) or descending (DESC) order for each column.
— GROUP BY: GROUP BY is used in conjunction with aggregate functions like SUM, AVG, COUNT, etc., to group rows that have the same values in specified columns. It creates summary rows for each group.
— WHERE: WHERE is used to filter rows based on specified conditions. It allows you to specify logical operators (AND, OR, NOT) and comparison operators (=, <>, >, <, >=, <=) to narrow down the result set.
— Alias: Aliases provide temporary names for columns or tables in SQL queries. They are useful for making query results more readable and for referencing columns with long names or complex expressions.
— JOIN: JOIN operations are used to combine rows from two or more tables based on a related column between them. Common types of joins include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.
— Functions: SQL functions perform operations on data or return specific values. Aggregate functions like SUM, AVG, MIN, MAX, and COUNT operate on a set of values, while scalar functions like UPPER, LOWER, CONCAT, and SUBSTRING operate on single values.
— Window Functions: Window functions perform calculations across a set of table rows related to the current row. They are useful for calculating running totals, moving averages, and ranking rows based on specified criteria.

2. DDL (Data Definition Language):**
— CREATE: CREATE statements are used to create database objects such as tables, views, indexes, sequences, etc. You specify the object’s name, columns, data types, constraints, and other properties.
— SELECT: In DDL, SELECT is used to retrieve metadata information about database objects like tables, views, columns, indexes, etc. It is not used for querying data.
— INSERT: INSERT statements add new rows of data into a table. You specify the table name and provide values for the columns or use a SELECT statement to insert data from another table.
— UPDATE: UPDATE statements modify existing data in a table by changing the values of specified columns in one or more rows based on specified conditions.
— DELETE: DELETE statements remove rows from a table based on specified conditions. It is used to delete specific data from the table without deleting the entire table.