Basic SQL Statements Flashcards

In Oracle SQL, which pseudo-table is used when you want to SELECT an expression or function without referencing a real table?

Answer: DUAL

DUAL is a special one-row, one-column dummy table in Oracle used to evaluate expressions that don't require a real table.

What does the BETWEEN operator include in its range?

Answer: Both the lower and upper bounds

BETWEEN x AND y is inclusive; it matches values greater than or equal to x AND less than or equal to y.

Which of the following correctly inserts a row with specific column values?

Answer: INSERT INTO EMPLOYEES VALUES (101, 'Ana');

The correct Oracle syntax is INSERT INTO table_name [(columns)] VALUES (values).

What is a column alias in SQL?

Answer: A temporary label given to a column in the query result

A column alias (using AS or a space) gives a temporary name to the column in the output without changing the underlying table.

Which SQL function converts a string to uppercase?

Answer: UPPER

UPPER(string) returns the string with all characters converted to uppercase letters.

What does SELECT * FROM employees WHERE salary IS NULL return?

Answer: Rows where salary has no value stored

IS NULL tests for the absence of a value; it returns rows where the salary column has no stored value.

Which clause is required in every valid SELECT statement in Oracle?

Answer: FROM

Every SELECT statement requires a FROM clause to specify the data source (though DUAL can be used for expression-only queries).