Home » Oracle » 1z0-051 » 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_idx1ON ord(ord_no);
B. CREATE INDEX ord_idx2ON ord_items(ord_no);
C. CREATE INDEX ord_idx3ON ord_items(item_no);
D. CREATE INDEX ord_idx4ON 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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“why there is not a answer A. CREATE INDEX ord_idx1ON ord(ord_no); its also true”
No, because ord_no its a primary key in ord table, so its have on index created automaticly when this constraint was created with the table. d
why there is not a answer A. CREATE INDEX ord_idx1ON ord(ord_no); its also true