Home » Oracle » 1z0-061 » Which two CREATE INDEX statements are valid?
View the Exhibit and examine the structure of ORD and ORD_ITEMS tables.
The ORD_NO column is PRIMARY KEY in the ORD table and the ORD_NO and ITEM_NO columns are composite PRIMARY KEY in the ORD_ITEMS table.
Which two CREATE INDEX statements are valid? (Choose two.)
A. CREATE INDEX ord_idx1
ON ord(ord_no);
B. CREATE INDEX ord_idx2
ON ord_items(ord_no);
C. CREATE INDEX ord_idx3
ON ord_items(item_no);
D. CREATE INDEX ord_idx4
ON ord, ord_items(ord_no, ord_date, qty);
Correct Answer: BC
Explanation/Reference:
Explanation:
How Are Indexes Created?
You can create two types of indexes.
Unique index: The Oracle server automatically creates this index when you define a column in a table to have a PRIMARY KEY or a UNIQUE constraint. The name of the index is the name that is given to the constraint.
Nonunique index: This is an index that a user can create. For example, you can create the FOREIGN KEY column index for a join in a query to improve the speed of retrieval.
Note: You can manually create a unique index, but it is recommended that you create a unique constraint, which implicitly creates a unique index.
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answers are not clear….
A is incorrect because you can’t create index for a field that was already indexed
B is correct because it is perfectly fine to create a designated index for a field that was part of composite index
C is correct because it is perfectly fine to create a designated index for a field that was part of composite index
D is incorrect because you can’t create composite index for same fields in same order that was already indexed, but if you change the order of fields than an index will be created , for instance :
create index ord_idx5 on ord_items(item_no, ord_no);
so correct answers BC