Rohan is learning to work upon Relational Database Management System (RDBMS) application. Help him to perform

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Q. Rohan is learning to work upon Relational Database Management System (RDBMS) application. Help him to perform the following tasks:

(a) To open the database named "LIBRARY".

(b) To display the names of all the tables stored in the opened database.

Uttar Pradesh UpmspCBSE Class XII Board 2022Subjective· 3mImportance★★★★★

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Concept understanding — SQL Query Concepts

SQL Query Concepts — A First Look

Think of a library. You walk in, and instead of wandering through endless shelves, you go to the librarian and say: "Give me all the books by Tagore published after 1950, sorted by title." The librarian knows exactly where everything is, finds what you asked for, and hands you the list. That's what SQL does — but for data stored in a computer.

SQL stands for Structured Query Language. It is the language we use to talk to databases. A database is just a collection of related information stored in tables — like an Excel workbook with multiple sheets, but far more powerful and organised.

The core idea: tables and queries

A database stores data in tables. Each table has rows (records) and columns (fields). For example, a Students table might have columns like RollNo, Name, City, and Marks. Each row is one student's complete information.

A query is simply a question you ask the database. You write it in SQL, and the database returns an answer — usually a new table made from the data that matches your question.

Note

SQL is not a programming language like Python or Java. You don't tell the computer how to find the data. You only say what data you want. The database figures out the fastest way to get it.

The most common SQL command: SELECT

Almost every query begins with SELECT. It means "show me this data." The basic structure is:

SELECT column1, column2 FROM table_name WHERE condition;

Read it like a sentence: "Select these columns from this table where this condition is true."

If you want all columns, you write SELECT *. The asterisk is a shortcut meaning "everything."

Filtering with WHERE

The WHERE clause is your filter. It keeps only the rows that satisfy a condition. For example, if you want students from Delhi only, you write:

SELECT * FROM Students WHERE City = 'Delhi';

You can combine conditions using AND (both must be true) and OR (at least one must be true). This is exactly like everyday logic: "Show me students from Delhi AND who scored above 80."

Sorting with ORDER BY

Data often comes back in no particular order. To arrange it, use ORDER BY. You can sort ascending (smallest first, which is the default) or descending (largest first) using DESC.

SELECT Name, Marks FROM Students ORDER BY Marks DESC;

This gives you a ranked list — highest marks first.

Why SQL matters for commerce and humanities

You will never calculate a formula in SQL. That is not what it does. What SQL does is organise, filter, and retrieve information — and that is the foundation of every data-driven decision. …

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To help Rohan perform these tasks in an RDBMS application, he would use the following standard SQL commands:

To open the database named "LIBRARY", Rohan should execute the command:

USE LIBRARY;
To display the names of all tables stored in the currently opened database, he should use:

SHOW TABLES;
To display the structure of the table "BOOKS" within the "LIBRARY" database, the command is: …

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To manage a database, you first select it with USE LIBRARY;, then list its tables using SHOW TABLES;, and finally inspect a specific table's structure with DESCRIBE BOOKS;.

When working with a Relational Database Management System (RDBMS), like MySQL or PostgreSQL, understanding how to navigate and inspect your data structures is fundamental. Think of a database as a large filing cabinet, and tables as individual folders within it. Before you can work with the documents (data) inside a folder, you first need to open the correct cabinet, then see which folders are available, and finally, understand the layout of a specific folder. Rohan's tasks mirror these essential steps in the digital world of databases.

(a) To open the database named "LIBRARY"

In an RDBMS, "opening" a database typically means selecting it as the active database for subsequent operations. You might have many databases on a single server, each serving a different purpose (e.g., one for a library, one for student records, one for inventory). To tell the system which database you intend to work with, you use a specific command. This command ensures that any table-related operations you perform next will apply to the tables within that chosen database.

The standard SQL command to select a database is:

USE LIBRARY;

After executing this command, the RDBMS will direct all your subsequent queries (until you USE another database or disconnect) to the "LIBRARY" database.

Note

The USE command doesn't actually "open" a file in the traditional sense; rather, it sets the current context for your session, telling the database server which specific database you want to interact with.

(b) To display the names of all the tables stored in the opened database

Once you've selected your database, the next logical step is often to see what data collections (tables) it contains. This is like looking at the labels on all the folders inside your chosen filing cabinet. Knowing the table names is crucial because you need them to query data, modify structures, or perform any operation on the data itself.

To list all the tables within the currently active database ("LIBRARY" in this case), you use the following SQL command:

SHOW TABLES;

This command will return a list of all the tables that exist within the "LIBRARY" database, allowing you to see at a glance what data sets are available for you to work with.

(c) To display the structure of the table "BOOKS" existing in the already opened database "LIBRARY"

After identifying the tables, you often need to understand their internal structure. What columns does the "BOOKS" table have? What kind of data can each column hold (e.g., text, numbers, dates)? Are there any constraints, like a column that must contain unique values? This information is vital for writing correct queries, inserting new data, or understanding how different pieces of information are stored. It's like examining a specific folder to see what kind of sections it has (e.g., "Title," "Author," "ISBN," "Publication Date") and what type of information is expected in each section. …

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Q.Rohan is learning to work upon Relational Database Management System (RDBMS) application. Help him to perform the following tasks:

(a) To open the database named "LIBRARY"

(b) To display the names of all the tables stored in the opened database

(c) To display the structure of the table "BOOKS" existing in the already opened database "LIBRARY"

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