Write the output of SQL queries (a) to (d) based on the table VACCINATIONDATA given below: Table: VACCINATIOND

Question 76 of 95

Q. Write the output of SQL queries

(a) to

(d) based on the table VACCINATION_DATA given below: Table: VACCINATION_DATA VID Name Age Dose1 Dose2 City 101 Jenny 27 2021-12-25 2022-01-31 Delhi 102 Harjot 55 2021-07-14 2021-10-14 Mumbai 103 Srikanth 43 2021-04-18 2021-07-20 Delhi 104 Gazala 75 2021-07-31 NULL Kolkata 105 Shiksha 32 2022-01-01 NULL Mumbai

(a) SELECT Name, Age FROM VACCINATION_DATA WHERE Dose2 IS NOT NULL AND Age > 40;

(b) SELECT City, COUNT(*) FROM VACCINATION_DATA GROUP BY City;

(d) SELECT MAX(Dose1), MIN(Dose2) FROM VACCINATION_DATA;

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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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The table VACCINATION_DATA stores vaccination records with VID as the unique identifier for each person. Each query retrieves specific information by filtering, grouping, or aggregating the data.

(a) This query selects the name and age of people who have received both doses (Dose2 is not NULL) and are older than 40. Looking at the table, Harjot (55, both doses given) and Srikanth (43, both doses given) meet both conditions. Gazala has only one dose, so she is excluded.

Output:

Name      Age
Harjot    55
Srikanth  43

(b) This query counts how many people are vaccinated in each city by grouping records by City. Delhi has 2 entries (Jenny and Srikanth), Mumbai has 2 (Harjot and Shiksha), and Kolkata has 1 (Gazala).

Output:

City      COUNT(*)
Delhi     2
Mumbai    2
Kolkata   1

(c) This query lists all unique cities present in the table without repetition. Three distinct cities appear: Delhi, Mumbai, and Kolkata.

Output:

City
Delhi
Mumbai
Kolkata
``` …

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These SQL queries retrieve filtered records, aggregate counts by city, list unique cities, and find extreme vaccination dates from the VACCINATION_DATA table.

Understanding the Table Structure

The VACCINATION_DATA table tracks vaccination records for five individuals. Each row contains a unique identifier (VID), personal details (Name, Age), two dose dates (Dose1, Dose2), and the City of residence. Notice that Gazala and Shiksha have NULL values in Dose2, meaning they haven't received their second dose yet—this detail matters when filtering or aggregating data.

Query (a): Filtering by Age and Completion Status

SELECT Name, Age FROM VACCINATION_DATA WHERE Dose2 IS NOT NULL AND Age > 40;

This query asks for names and ages of people who meet two conditions: they must have completed both doses (Dose2 IS NOT NULL) and be older than 40. Walking through the table:

Jenny (27) fails the age test
Harjot (55) passes both—has Dose2 and is over 40
Srikanth (43) passes both—has Dose2 and is over 40
Gazala (75) passes the age test but has NULL in Dose2
Shiksha (32) fails both conditions

Output:

Name	Age
Harjot	55
Srikanth	43

Query (b): Counting Records by City

SELECT City, COUNT(*) FROM VACCINATION_DATA GROUP BY City;

GROUP BY collapses rows sharing the same City value into groups, and COUNT(*) tallies how many records fall into each group. Delhi appears twice (Jenny, Srikanth), Mumbai twice (Harjot, Shiksha), and Kolkata once (Gazala).

Output:

City	COUNT(*)
Delhi	2
Mumbai	2
Kolkata	1

Note

The order of cities in the output depends on the database implementation—SQL doesn't guarantee any particular sequence unless you add ORDER BY.

Query (c): Listing Unique Cities

SELECT DISTINCT City FROM VACCINATION_DATA;

DISTINCT eliminates duplicate values, so even though Delhi and Mumbai each appear twice in the table, they're listed only once in the result.

Output:

City
Delhi
Mumbai
Kolkata

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Q.Write the output of SQL queries

Understanding the Table Structure

Query (a): Filtering by Age and Completion Status

Query (b): Counting Records by City

Query (c): Listing Unique Cities

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