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Indexes for the PRIMARY KEY Column in Oracle
What Is an Index Associated with a Constraint in Oracle?
✍: FYIcenter.com
An index associated with a constraint because this constraint is required to have an index. There are two types of constraints are required to have indexes: UNIQUE and PRIMARY KEY. When you defines a UNIQUE or PRIMARY KEY constraint in a table, Oracle will automatically create an index for that constraint. The following script shows you an example:
CREATE TABLE student (id NUMBER(5) PRIMARY KEY, first_name VARCHAR(80) NOT NULL, last_name VARCHAR(80) NOT NULL, birth_date DATE NOT NULL, social_number VARCHAR(80) UNIQUE NOT NULL); Table created. SELECT index_name, table_name, uniqueness FROM USER_INDEXES WHERE table_name = 'STUDENT'; INDEX_NAME TABLE_NAME UNIQUENES ----------------------- --------------------- --------- SYS_C004123 STUDENT UNIQUE SYS_C004124 STUDENT UNIQUE
The result confirms that Oracle automatically created two indexes for you.
2019-05-01, 736👍, 0💬
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