SQL and Database Fundamentals

A candidate key is a minimal set of attributes that uniquely identifies each row in a table. A table can have multiple candidate keys, and one is selected as the primary key.

Triggers cannot be called directly from application code. They are automatically executed by the database in response to specific events like INSERT, UPDATE, or DELETE operations on tables.

To solve this question, the user needs to know about views in database management systems. A view is a virtual table that does not store any data but only displays data from one or more tables in the database.

Based on this information, the correct answer is:

The Answer is: C. Virtual

SQL uses the COUNT aggregate function to return the number of rows in a table, either as COUNT(*) or COUNT(column_name). NUM and NUMBER are not valid SQL aggregate functions.

Outer joins (LEFT, RIGHT, FULL) do NOT require matching records - they return all records from one or both tables, with NULLs filling in for non-matching rows. Only inner joins require matches on both sides.

SHOW DATABASES LIKE 'tech%' correctly returns all databases whose names start with 'tech'. The % wildcard matches zero or more characters, so 'tech%' finds 'tech', 'technology', 'tech1', etc. Options A and C have the % in the wrong position (matches names containing 'tech'), and B has a syntax error with an unclosed quote.

A table can have multiple UNIQUE constraints, each enforcing uniqueness on a different column or combination of columns. This is different from a PRIMARY KEY, of which a table can only have one. UNIQUE constraints are commonly used on columns like email, username, or phone number where duplicates should not occur.

HAVING filters aggregated results after GROUP BY, while WHERE filters rows before aggregation. The key distinction is that HAVING can use aggregate functions (COUNT, SUM, AVG, etc.) but WHERE cannot. Option C is incomplete because simply 'using GROUP BY' doesn't guarantee HAVING is needed; HAVING is specifically for filtering the grouped aggregates.

The USE keyword in SQL selects a database as the active context for subsequent operations. For example, 'USE company_db;' makes 'company_db' the default database so you don't need to prefix table names. It does not select tables or columns; those are selected with SELECT statements.

ENUM values are stored as strings in the database, not as their underlying index numbers. While ENUM types do have an internal numeric index (1, 2, 3...), the actual storage uses the string representation. This is why ALTER TABLE can add new ENUM values without affecting existing data; the string value is what's persisted.

In Oracle, EXPLAIN PLAN results are written by default to a table named "plan_table" (with an underscore), not to flat files or space-separated names like "plan table". This allows querying and formatting of execution plans using DBMS_XPLAN.

In join operations, the driving table (accessed first by the optimizer) should typically be the smaller table or the one with the most selective filter condition. This minimizes intermediate result sets and improves overall join performance.

When you apply functions or expressions to indexed columns in WHERE clauses (e.g., WHERE UPPER(name) = 'TEST'), the optimizer cannot use the index on that column. This forces a full table scan instead of an efficient index range scan, severely degrading performance.

A UNION query requires that corresponding columns in both select statements have compatible data types. Here, the first SELECT returns a numeric value (1) while the second returns a character value ('A'), resulting in a data type mismatch error.

The AVG function ignores NULL values and calculates the average of non-NULL values only. (5 + 10) / 2 = 7.5. It does not return NULL, 5, or 10.

When all rows have been fetched from a cursor and another fetch is issued, the cursor continues to return the last record. It does not throw an error or return to the first record.

To solve this question, the user needs to have basic knowledge of SQL and the concept of the rownum keyword in SQL.

The rownum keyword is used to assign a unique number to each row returned by a query in Oracle. It is often used to limit the number of rows returned by a query.

Now, let's go through each option and explain why it is right or wrong:

A. 10th row: This option is incorrect. The rownum keyword assigns a unique number to each row returned by a query. However, the where clause in the given SQL limits the result set to only the row where rownum equals 10. This means that the SQL query will only return one row, and that row will be the 10th row in the result set.

B. 1st row: This option is incorrect. The where clause in the given SQL limits the result set to only the row where rownum equals 10. This means that the SQL query will only return one row, and that row will be the 10th row in the result set.

C. no rows returned: This option is incorrect. The SQL query will return one row, which is the 10th row in the result set.

D. First 10 rows: This option is incorrect. The where clause in the given SQL limits the result set to only the row where rownum equals 10. This means that the SQL query will only return one row, and that row will be the 10th row in the result set.

The Answer is: C

When a user creates an object without specifying a tablespace, Oracle stores it in that user's default tablespace. This is defined in the user profile. It does not use the system tablespace or throw an error.

MAX is an aggregate function that can operate on any standard data type including numbers, strings, and dates. Functions like CEIL require numbers, LOWER and LPAD require strings, and TO_CHAR does not accept all raw datatypes directly in the same way.

NEXT_DAY finds the first occurrence of the specified day after the given date. Starting from Monday July 10, the next Monday is July 17. The format mask 'DD-MON-RR' gives 17-JUL-00. The other options are incorrect dates.