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Oracle Database Interview Question:
What Happens to Indexes If You Drop a Table?
Submitted by: AdministratorIf you drop a table, what happens to its indexes? The answer is that if a table is dropped, all its indexes will be dropped too. Try the following script to see yourself:
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';
<pre>INDEX_NAME TABLE_NAME UNIQUENES
----------------------- --------------------- ---------
SYS_C004141 STUDENT UNIQUE
SYS_C004142 STUDENT UNIQUE
STUDENT_BIRTH_DATE STUDENT NONUNIQUE</pre>
DROP TABLE STUDENT;
Table dropped.
SELECT index_name, table_name, uniqueness
FROM USER_INDEXES WHERE table_name = 'STUDENT';
no data found
No records in USER_INDEXES view found for your name STUDENT, after you dropped STUDENT table.
Submitted by: Administrator
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';
<pre>INDEX_NAME TABLE_NAME UNIQUENES
----------------------- --------------------- ---------
SYS_C004141 STUDENT UNIQUE
SYS_C004142 STUDENT UNIQUE
STUDENT_BIRTH_DATE STUDENT NONUNIQUE</pre>
DROP TABLE STUDENT;
Table dropped.
SELECT index_name, table_name, uniqueness
FROM USER_INDEXES WHERE table_name = 'STUDENT';
no data found
No records in USER_INDEXES view found for your name STUDENT, after you dropped STUDENT table.
Submitted by: Administrator
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