Sql

In MYSQL, it is possible to retrieve records from multiple tables
using operations like JOIN, which combines rows based on related columns.
So, Assertion (A) is true.
A foreign key is a field in one table that refers to the primary key of another table,
which helps to establish a relationship between them — so Reason (R) is true too.
However, the foreign key does not itself perform the retrieval;
it only defines how tables relate.
The actual retrieval is done using queries like JOIN statements.
Therefore, Reason (R) is true but not the correct explanation for Assertion (A).
So, option (B) is correct.

A Cartesian product between two tables combines each row
of the first table with every row of the second table.
So, the total number of rows will be the product of the row counts:
6 rows in A multiplied by 5 rows in B equals 30 rows.
The number of columns in the resulting table
will be the sum of the columns from both tables:
3 columns in A plus 2 columns in B equals 5 columns.
So the statement is True.

In MYSQL, values for string data types like CHAR and VARCHAR
must be enclosed within quotation marks — either single or double quotes.
DATE values are also written in quotes,
because they are treated as string literals representing a date format.
However, numeric data types like FLOAT or INT
should be written without quotes.
If a number is enclosed in quotes, it is treated as a string,
which can cause data type mismatches and errors in queries.
Therefore, the correct answer is FLOAT.

In SQL, the COUNT() function is an aggregate function
used to count the number of rows that match a specified condition.
When used on a column, COUNT() counts only the non-NULL values.
It ignores any NULL entries in that column automatically.
len(), number(), and num() are not valid SQL aggregate functions.
len() exists in Python but not in SQL.
Therefore, the function that counts values ignoring NULLs is COUNT().
So, option (B) is correct.

SQL commands are categorized mainly as DML, DDL, and DCL.
DML (Data Manipulation Language) includes commands that modify data,
like INSERT, UPDATE, DELETE, and SELECT.
UPDATE is used to modify existing records in a table,
so it is a classic DML command.
CREATE and ALTER are DDL (Data Definition Language) commands,
which define or modify database structures like tables.
DROP is also a DDL command used to delete tables or databases.
Therefore, the only DML command here is UPDATE.

In database management, constraints are rules enforced on columns to ensure data integrity.
The UNIQUE constraint ensures that all values in a column are different.
It prevents duplicate values from being inserted into that column.
For example, you might set the email column to be UNIQUE so that no two records can have the same email address.
The DISTINCT keyword is used in SELECT queries to remove duplicate rows from the result but is not a constraint.
NOT NULL ensures that a column cannot have NULL values but allows duplicates.
HAVING is used with GROUP BY to filter groups, not to enforce data integrity on insert.
Therefore, the only option that prevents duplicate values at the table level is UNIQUE.
So, the correct answer is option (A).