多項(xiàng)選擇題

Which three statements about subqueries are true? （）

A. A main query can have more than one subquery.
B. A subquery can have more than one main query.
C. The subquery and main query must retrieve data from the same table.
D. The subquery and main query can retrieve data from different tables.
E. Only one column or expression can be compared between the subquery and main query.
F. Multiple columns or expression can be compared between the subquery and main query.

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單項(xiàng)選擇題

EXHIBIT, Emp Table

Exhibit A

Exhibit B

Examine the data from the EMP table.
Evaluate this SQL statement:
SELECT *
FROM emp
WHERE emp _ id = 3);
WHERE commission = (SELECT commission
FROM emp
What is the result when the query is executed?（）

A. Exhibit A
B. Exhibit B
C. The query returns no rows
D. The query fails because the outer query is retrieving more than one column
E. The query fails because both the inner and outer queries are retrieving data from the same table.

多項(xiàng)選擇題

Which two statements about creating constraints are true?（）

A. Constraint names must start with SYS_C
B. All constraints must be defines at the column level
C. Constraints can be created after the table is created
D. Constraints can be created at the same time the table is created
E. Information about constraints is found in the VIEW_CONSTRAINTS dictionary view

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Which three statements about subqueries are true? （）

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EXHIBIT, Emp Table Exhibit A Exhibit B Examine the data from the EMP table. Evaluate this SQL statement: SELECT * FROM emp WHERE emp _ id = 3); WHERE commission = (SELECT commission FROM emp What is the result when the query is executed?（）

Which two statements about creating constraints are true?（）

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EXHIBIT, Emp Table

Exhibit A

Exhibit B

Examine the data from the EMP table.
Evaluate this SQL statement:
SELECT *
FROM emp
WHERE emp _ id = 3);
WHERE commission = (SELECT commission
FROM emp
What is the result when the query is executed?（）