單項選擇題

In which scenario would an index be most useful?（）

A.The indexed column is declared as NOT NULL.
B.The indexed columns are used in the FROM clause.
C.The indexed columns are part of an expression.
D.The indexed column contains a wide range of values.

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單項選擇題

A subquery can be used to（）.

A.create groups of data
B.sort data in a specific order
C.convert data to a different format
D.retrieve data based on an unknown condition

單項選擇題

Click the Exhibit button to examine the data of the EMPLOYEES table. Evaluate this SQL statement:
SELECT e.employee_id "Emp_id", e.emp_name "Employee", e.salary, m.employee_id "Mgr_id", m.emp_name "Manager"
FROM employees e JOIN employees m ON (e.mgr_id = m.employee_id)
AND e.salary > 4000;
What is its output?（）

A.A
B.B
C.C
D.D
E.E

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In which scenario would an index be most useful?（）

你可能感興趣的試題

A subquery can be used to（）.

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