SQL_assignment.ipynb

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    "1>\n",
    "A database is essentially an organized collection of structured data, typically stored electronically on a computer system. This data is organized in a way that allows for efficient access, retrieval, manipulation, and analysis. Imagine it as a digital filing cabinet, but for information instead of paper documents.\n",
    "\n",
    "Now, there are two main types of databases: SQL and NoSQL. Here's a breakdown of their key differences:\n",
    "\n",
    "Structure:\n",
    "\n",
    "SQL (Structured Query Language): These databases follow a relational structure, meaning data is organized into tables with predefined schemas. Think of a table like a spreadsheet with rows and columns, where each column represents a specific data attribute (e.g., name, age, city) and each row represents an individual record (e.g., information about a specific person). The schema defines the data types and constraints for each attribute, ensuring consistency and data integrity.\n",
    "\n",
    "NoSQL (Not Only SQL): As the name suggests, NoSQL databases are non-relational. They offer more flexible data models, allowing for storing data in various formats like documents, key-value pairs, graphs, or wide-column stores. This flexibility comes in handy when dealing with unstructured or semi-structured data, which doesn't easily fit into rigid table structures."
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    "2>\n",
    "DDL stands for Data Definition Language. It's a category of SQL (Structured Query Language) commands specifically designed to work with the structure of database objects such as tables, views, indexes, and more. Here's a breakdown of the DDL commands you mentioned, along with examples:\n",
    "\n",
    "1.CREATE\n",
    "\n",
    "Purpose: The CREATE command is used to bring new database objects into existence. This includes:\n",
    "\n",
    "Tables: Defining the basic structure of how your data will be stored (columns, data types, constraints).\n",
    "Views: Creating virtual tables that represent a calculated or filtered version of existing table data.\n",
    "Indexes: Creating structures that help speed up data retrieval from tables.\n",
    "Example: Creating a table for customers\n",
    "CREATE TABLE Customers (\n",
    "    CustomerID INT PRIMARY KEY, \n",
    "    CustomerName VARCHAR(50) NOT NULL,\n",
    "    Address VARCHAR(255),\n",
    "    City VARCHAR(50)\n",
    ");\n",
    "\n",
    "2.DROP\n",
    "\n",
    "Purpose: The DROP command is the opposite of CREATE. It permanently deletes entire database objects. Be very careful with this command, as the deletion is irreversible!\n",
    "\n",
    "Example: Deleting a table\n",
    "DROP TABLE Customers; \n",
    "\n",
    "3.ALTER\n",
    "\n",
    "Purpose:  The ALTER command lets you modify the structure of an existing database object. Some common modifications include:\n",
    "\n",
    "Adding new columns: Introducing new data fields to a table.\n",
    "Modifying columns: Changing data types or constraints of existing columns.\n",
    "Removing columns: Dropping columns that are no longer needed.\n",
    "Renaming objects: Changing the name of a table, view, or index.\n",
    "Example: Adding an email column to the Customers table.\n",
    "ALTER TABLE Customers \n",
    "ADD Email VARCHAR(255);\n",
    "\n",
    "4.TRUNCATE\n",
    "\n",
    "Purpose: The TRUNCATE command is used to quickly remove all rows of data from a table without deleting the table structure itself. It's functionally similar to a DELETE command without a WHERE clause, but is  generally faster and more efficient.\n",
    "\n",
    "Example: Clearing out all data from the Customers table\n",
    "TRUNCATE TABLE Customers;"
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    "3>\n",
    "DML stands for Data Manipulation Language. This category of SQL (Structured Query Language) commands focuses on the actual data stored within database objects. DML commands are what you'll use most often to work with the information within your databases.\n",
    "\n",
    "Let's look at the key DML commands you asked about:\n",
    "\n",
    "1 INSERT\n",
    "\n",
    "Purpose: The INSERT command is used to add new rows of data into an existing table.\n",
    "\n",
    "Example: Adding a new customer to the Customers table\n",
    "\n",
    "SQL\n",
    "INSERT INTO Customers (CustomerID, CustomerName, Address, City)\n",
    "VALUES (101, 'Sarah Johnson', '123 Main Street', 'New York'); \n",
    "\n",
    "2.UPDATE\n",
    "\n",
    "Purpose:  The UPDATE command modifies existing data within a table. You can update one or more columns for specific records that match a condition.\n",
    "\n",
    "Example: Changing a customer's address\n",
    "\n",
    "SQL\n",
    "UPDATE Customers \n",
    "SET Address = '456 Elm Street', City = 'Los Angeles'\n",
    "WHERE CustomerID = 101;\n",
    "Use code with caution.\n",
    "3.DELETE\n",
    "\n",
    "Purpose: The DELETE command removes one or more rows from a table. It's often used with a WHERE clause to specify which rows to delete.\n",
    "\n",
    "Example: Removing a customer from the table\n",
    "\n",
    "SQL\n",
    "DELETE FROM Customers \n",
    "WHERE CustomerID = 102;"
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    "4>\n",
    "DQL stands for Data Query Language. It's a category of SQL commands specifically focused on retrieving data from existing database objects (tables, views, etc.). The SELECT statement is the primary command used in DQL.  Think of DQL as the language for asking your database questions.\n",
    "\n",
    "SELECT Statement\n",
    "\n",
    "Purpose: The SELECT statement fetches data from database tables based on the criteria you specify. It has the following general structure:\n",
    "\n",
    "SQL\n",
    "SELECT column1, column2, ... \n",
    "FROM table_name\n",
    "[WHERE condition]\n",
    "[ORDER BY column1 ASC/DESC]\n",
    "... (other optional clauses)"
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    "5>\n",
    "Absolutely! Here's an explanation of Primary Keys and Foreign Keys, essential concepts in relational database design:\n",
    "\n",
    "Primary Key\n",
    "\n",
    "Purpose: A primary key is a column (or a combination of columns) within a table that uniquely identifies each row (record) in that table. Think of it as the ID card of each record that can't be duplicated.\n",
    "Properties:\n",
    "Unique: Each value in the primary key column must be different.\n",
    "Not Null: A primary key column cannot contain null (empty) values.\n",
    "Benefits:\n",
    "Data Integrity: Primary keys ensure that no two records have the same identifier, which prevents duplicate data.\n",
    "Relationships: Primary keys serve as the basis for creating relationships with other tables (explained in the Foreign Key section).\n",
    "Example: In a Customers table, CustomerID could be the primary key.\n",
    "Foreign Key\n",
    "\n",
    "Purpose: A foreign key is a column (or a combination of columns) within a table that creates a link to the primary key of another table. It represents a relationship between those two tables.\n",
    "How it works: The values in the foreign key column must match existing values in the primary key column of the referenced table.\n",
    "Benefits:\n",
    "Referential Integrity: Foreign keys enforce data consistency between related tables. You cannot add a record to the table containing the foreign key if the value doesn't already exist in the referenced table's primary key. This prevents dangling references and orphaned data.\n",
    "Data Navigation: Foreign keys enable easy retrieval and joining of related information across tables.\n",
    "Example:\n",
    "\n",
    "Customers Table\n",
    "\n",
    "CustomerID (Primary Key)\n",
    "CustomerName\n",
    "City\n",
    "Orders Table\n",
    "\n",
    "OrderID (Primary Key)\n",
    "CustomerID (Foreign Key referencing the Customers table)\n",
    "OrderDate\n",
    "Key Points\n",
    "\n",
    "One table can have multiple foreign keys referencing different tables.\n",
    "It's common (but not always required) for a foreign key to have the same name as the primary key it references.\n",
    "Let me know if you'd like a more visual diagram or specific scenarios to illustrate how primary and foreign keys work together!\n",
    "\n"
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    "6>\n",
    "\n",
    "import mysql.connector\n",
    "\n",
    "# Database connection details (replace with your actual credentials)\n",
    "mydb = mysql.connector.connect(\n",
    "    host=\"your_database_host\",\n",
    "    user=\"your_username\",\n",
    "    password=\"your_password\",\n",
    "    database=\"your_database_name\"\n",
    ")\n",
    "\n",
    "# Create a cursor object\n",
    "my_cursor = mydb.cursor()\n",
    "\n",
    "# Example SQL query\n",
    "sql_query = \"SELECT * FROM Customers\"\n",
    "\n",
    "# Execute the SQL query\n",
    "my_cursor.execute(sql_query)\n",
    "\n",
    "# Fetch the results (if any)\n",
    "result = my_cursor.fetchall()\n",
    "\n",
    "# Print the fetched data\n",
    "for row in result:\n",
    "    print(row)\n",
    "\n",
    "# Close the cursor and database connection\n",
    "my_cursor.close()\n",
    "mydb.close()\n",
    "\n",
    "Explanation:\n",
    "\n",
    "Import the mysql.connector library: This library provides the necessary functions to interact with a MySQL database from Python.\n",
    "\n",
    "connect() function:\n",
    "\n",
    "host: The hostname or IP address of the MySQL server.\n",
    "user: Your username for the MySQL database.\n",
    "password: Your password for the MySQL database.\n",
    "database: The name of the specific database you want to connect to.\n",
    "cursor() method:\n",
    "\n",
    "A cursor is a database object that allows you to execute SQL statements and iterate over the results. Think of it as a pointer into the result set of a query.\n",
    "execute() method:\n",
    "\n",
    "This method takes an SQL query as a string argument.\n",
    "It executes the SQL query against the database that the cursor is connected to.\n",
    "fetchall() method (optional):\n",
    "\n",
    "Used to retrieve all rows in the result set.\n",
    "Returns the data as a list of tuples (each tuple representing a row).\n",
    "Closing connections: It's essential to close the cursor and database connection when you're done with them to release resources.\n",
    "\n",
    "Absolutely! Here's a breakdown of the cursor() and execute() methods, commonly used for database interactions in Python and other languages.\n",
    "\n",
    "cursor() method\n",
    "\n",
    "Role: The cursor() method creates a cursor object.  This object acts as your temporary workspace within the database and serves as a way to traverse and work with the results of your queries. Consider it like a pointer into your database results.\n",
    "\n",
    "Key Actions:  Cursors allow you to:\n",
    "\n",
    "Execute SQL Queries: They help you submit SQL statements to the database for execution.\n",
    "Retrieve Results: Fetch the data generated by your queries in a controlled manner (all at once, row by row, etc.).\n",
    "Manage Transactions: Cursors may be involved in managing database transactions, ensuring changes are either committed or rolled back as a single unit.\n",
    "execute() method\n",
    "\n",
    "Role:  The execute() method is associated with a cursor object. Its primary function is to execute the SQL statement you provide.\n",
    "\n",
    "How it works\n",
    "\n",
    "SQL Statement: You pass an SQL query string (e.g., \"SELECT * FROM Customers\") to the execute() method.\n",
    "Execution: The cursor takes this SQL statement and sends it to the database server for execution.\n",
    "Results (if applicable): If the SQL statement returns a result set (e.g., data from a SELECT query), the cursor prepares it for retrieval.\n",
    "Typical Workflow\n",
    "\n",
    "Connect to the database: Establish a connection to the database you want to work with.\n",
    "Create a cursor object: Call the cursor() method on your database connection object.\n",
    "Execute SQL statements: Use the cursor's execute() method to send SQL commands to the database.\n",
    "Fetch and process results: Use methods like fetchone(), fetchall(), or fetchmany() to retrieve query results from the cursor (if applicable).\n",
    "Close connections: Always close the cursor and database connections when you're finished working with them."
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    "7>\n",
    "FROM and JOIN clauses:\n",
    "\n",
    "The FROM clause, along with any JOIN clauses, are executed first. This step identifies and combines the necessary tables involved in the query.\n",
    "If subqueries are present within the FROM clause, they are also evaluated at this stage.\n",
    "WHERE clause:\n",
    "\n",
    "After identifying the relevant data, the WHERE clause filters the data based on the specified conditions. Rows that don't meet the filtering criteria are removed from the result set.\n",
    "GROUP BY clause (if present):\n",
    "\n",
    "If the query includes a GROUP BY clause, it groups the remaining rows based on the specified column(s). This step prepares the data for aggregate functions.\n",
    "HAVING clause (if present):\n",
    "\n",
    "The HAVING clause, used in conjunction with GROUP BY, applies additional filtering conditions to the groups created in the previous step. Only groups that satisfy the HAVING condition are retained.\n",
    "SELECT clause:\n",
    "\n",
    "The SELECT clause determines which columns and expressions are included in the final result set. This involves calculating any expressions or applying aliases to columns.\n",
    "DISTINCT clause (if present):\n",
    "\n",
    "If the DISTINCT keyword is present, it removes duplicate rows from the result set based on the selected columns.\n",
    "ORDER BY clause (if present):\n",
    "\n",
    "The ORDER BY clause sorts the final result set based on the specified column(s) and order (ascending or descending).\n",
    "LIMIT and OFFSET clauses (if present):\n",
    "\n",
    "The LIMIT clause specifies the maximum number of rows to be returned in the result set.\n",
    "The OFFSET clause, used with LIMIT, indicates the number of rows to skip from the beginning of the result set before starting to return rows.\n"
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