Structured Query Language Quiz Class 12

✅ Answer: (c) Structured Query Language

SQL stands for Structured Query Language — the standard language used to create, manage, and query relational databases.

✅ Answer: (c) To define and manage the structure of a database

DDL commands (CREATE, ALTER, DROP) are used to define and manage the structure of databases and tables — as opposed to DML, which manipulates the actual data inside them.

✅ Answer: (c) VARCHAR(n)

VARCHAR(n) stores text up to n characters, using only as much space as the actual text needs. CHAR(n), by contrast, always reserves the full n characters, padding shorter values with spaces.

✅ Answer: (b) Disallows NULL values in the column

NOT NULL forces a column to always have a value — attempting to insert a row without one for that column will be rejected.

✅ Answer: (a) CREATE DATABASE database_name;

CREATE DATABASE database_name; is the correct command. USE switches to an existing database, SHOW DATABASES lists them, and DROP DATABASE deletes one entirely.

✅ Answer: (c) To retrieve data from a table

SELECT is used purely to retrieve (query) data from one or more tables — it’s the most frequently used SQL statement.

✅ Answer: (b) Retrieves unique values from a specified column

DISTINCT filters out repeated values, returning only the unique ones from the specified column(s) — e.g. SELECT DISTINCT Class FROM Students; lists each class name just once, no matter how many students are in it.

✅ Answer: (b) SELECT * FROM table_name WHERE condition;

SELECT * FROM table_name WHERE condition; is the standard pattern to retrieve only the rows matching a given condition. (The other three options also correctly use WHERE, but for DELETE/UPDATE purposes rather than a basic SELECT filter.)

✅ Answer: (b) To group rows that have the same values in specified columns

GROUP BY collects rows sharing the same value in a given column into groups — almost always paired with an aggregate function like COUNT(), SUM(), or AVG() to summarize each group.

✅ Answer: (a) SELECT * FROM table1, table2 WHERE table1.column = table2.column;

The CBSE Class 12 syllabus specifically teaches equi-join using comma-separated tables in the FROM clause combined with an equality condition in WHERE — e.g. SELECT * FROM table1, table2 WHERE table1.id = table2.id;. (This question is corrected/clarified from a version whose options included LEFT/RIGHT JOIN syntax, which are outer joins not covered in this syllabus and aren’t examples of an equi-join at all — an equi-join specifically means joining on an equality condition, which the comma+WHERE method demonstrates directly.)

✅ Answer: (b) Modifies existing records in a table

UPDATE changes the values of existing rows that match a given condition — e.g. UPDATE Students SET Marks = 90 WHERE RollNo = 1;.

✅ Answer: (a) DELETE

DELETE removes rows matching a condition from a table (e.g. DELETE FROM Students WHERE RollNo = 3;). Note that DROP is different — it removes the entire table structure, not just some rows.

✅ Answer: (b) To filter the results of aggregate functions AFTER grouping

HAVING filters groups based on aggregate results (like HAVING AVG(Marks) > 85), applied after GROUP BY has run — this is exactly why HAVING can filter on aggregates, whereas WHERE (which runs before grouping) cannot.

✅ Answer: (b) Retrieves the maximum value in a column

MAX() returns the largest value found in the specified column across the matching rows.

✅ Answer: (a) The result of combining every row of one table with every row of another, giving rows = (rows in table1) × (rows in table2)

A Cartesian product (from SELECT * FROM table1, table2; with no WHERE condition) pairs every row of the first table with every row of the second — a 5-row table joined with a 2-row table produces 5 × 2 = 10 resulting rows.

✅ Answer: (b) CHAR(n) always uses exactly n characters of storage (padding shorter values with spaces); VARCHAR(n) uses only as much space as the actual value needs, up to n

CHAR(n) is fixed-length — a value shorter than n gets padded with trailing spaces to fill it exactly. VARCHAR(n) is variable-length — it only uses as much storage as the actual text requires, up to the maximum n.

✅ Answer: (b) A natural join automatically matches columns with the same name across both tables and removes the duplicate column from the result; an equi-join requires an explicit equality condition and keeps both columns

A natural join automatically finds columns with matching names in both tables, joins on them, and shows that shared column just once in the result. An equi-join requires you to explicitly write the equality condition (e.g. WHERE t1.id = t2.id), and the result keeps both copies of the joined column (from each table).

✅ Answer: (b) LIKE

LIKE, combined with wildcard characters, does pattern matching — e.g. WHERE Name LIKE 'R%' matches any name starting with “R” (the % matches any sequence of characters).

✅ Answer: (c) BETWEEN

BETWEEN low AND high selects all values falling within that range, including both endpoints — e.g. WHERE Marks BETWEEN 80 AND 90 includes marks of exactly 80 and exactly 90 too.

✅ Answer: (b) One row per class, showing the average marks for each class

GROUP BY Class collects all rows into groups by class, and AVG(Marks) computes the average within each group — so the result has exactly one row per distinct class, each showing that class’s average marks.