Q.To display the name and date of birth of student with roll number 2, we write the following query:

What is a SELECT Query?

Imagine you have a giant notebook — a register of every student in your school, with columns for Roll Number, Name, Class, and Marks. If someone asks "Who scored above 90%?", you don't read the whole notebook aloud. You flip through, pick only the rows that match, and maybe even write down just the names.

That's exactly what a SELECT query does in a database. It's your way of asking the database: "Show me specific information from this table, under these conditions."

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The Intuition First

A table is just rows and columns. A SELECT query lets you:

• Choose which columns you want to see (like picking only Name and Marks, ignoring Roll Number)
• Choose which rows you want (like only students in Class 12, or only those with Marks > 90)
• Optionally sort the results, group them, or rename the columns for clarity

You are not changing the original table — you are just querying it, like asking a question and getting a printed answer.

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The Precise Statement

The simplest form of a SELECT query is:

SELECT column1, column2, ...
FROM table_name;

If you want every column, use * (a wildcard meaning "all columns"):

SELECT * FROM Students;

That gives you the entire table, unchanged.

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Adding Conditions: The WHERE Clause

Most real queries need a filter. You add a WHERE clause:

SELECT Name, Marks
FROM Students
WHERE Marks > 90;

This says: "From the Students table, show me only the Name and Marks columns, but only for rows where Marks is greater than 90."

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Sorting Results: ORDER BY

To arrange the output in a specific order:

SELECT Name, Marks
FROM Students
WHERE Class = '12A'
ORDER BY Marks DESC;

DESC means descending (highest first). ASC (ascending) is the default if you don't specify.

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Renaming Columns: Aliases

Sometimes the column name in the table is cryptic (like mrks or stu_name). You can rename it in the output using AS:

SELECT Name AS StudentName, Marks AS Percentage
FROM Students;

The table still has the original column names — only the result sheet shows your chosen labels.

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A Complete Example

Suppose you have a table called Employees: