How To Drop an Index in Oracle?

If you don't need an existing index any more, you should delete it with the DROP INDEX statement. Here is an example SQL script:

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.

CREATE INDEX student_birth_date ON student(birth_date);
Index created.

SELECT index_name, table_name, uniqueness 
  FROM USER_INDEXES WHERE table_name = 'STUDENT';
INDEX_NAME              TABLE_NAME            UNIQUENES
----------------------- --------------------- ---------
SYS_C004129             STUDENT               UNIQUE
SYS_C004130             STUDENT               UNIQUE
STUDENT_BIRTH_DATE      STUDENT               NONUNIQUE 

DROP INDEX STUDENT_BIRTH_DATE;
Index dropped.

⇒Managing Oracle Table Indexes

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