ABE IS CORRECT
A-TRUE
B-TRUE
C-FALSE
D-FALSE: The database automatically maintains indexes when you insert, update, and delete rows of
the associated table. If you drop an index, all applications continue to work. However,
access to previously indexed data might be slower.
E-TRUE
F-FALSE:Unlike unusable indexes, an invisible index is maintained during DML statements
SQL> create index a1 on x1(b1);
Index created.
SQL> create unique index a2 on x1(b1);
create unique index a2 on x1(b1)
*
ERROR at line 1:
ORA-01408: such column list already indexed
SQL>
C is correct:
SQL> create table t1 (col1 number, col2 varchar2(10), col3 varchar2(10));
Table created.
Elapsed: 00:00:00.03
SQL> create unique index ix1 on t1(col1);
Index created.
Elapsed: 00:00:00.02
SQL> create index ix2 on t1(col1, col2);
Index created.
Elapsed: 00:00:00.01
SQL> create unique index ix3 on t1(col1, col2, col3);
Index created.
Elapsed: 00:00:00.02
SQL>
A-
CREATE TABLE Books(
ID NUMBER PRIMARY KEY USING INDEX (CREATE INDEX idx_custom_books_id ON books (ID)),
Title VARCHAR2(100) NOT NULL,
Author VARCHAR2(100) NOT NULL,
PublishYear NUMBER NOT NULL
);
C- "Oracle Database treats descending indexes as if they were function-based indexes"
https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/CREATE-INDEX.html#GUID-1F89BBC0-825F-4215-AF71-7588E31D8BFE__GUID-92F4F0FB-499A-4ED7-8630-B219F8A50B90
E- "When you have multiple indexes on the same set of columns, only one of these indexes can be visible at a time, and any other indexes must be invisible."
"You can create multiple indexes on the same set of columns when at least one of the following index characteristics is different:
The indexes have different uniqueness properties.
You can create both a unique and a non-unique index on the same set of columns."
https://docs.oracle.com/en/database/oracle/oracle-database/19/admin/managing-indexes.html#GUID-B4B30CF4-2B95-44D6-8596-EC2A378251EF
Correct is ACE, according the above evidences.
E is false:
-- Create table
CREATE TABLE test_table (
id NUMBER,
value VARCHAR2(255)
);
-- Populate the table
INSERT INTO test_table (id, value) VALUES (1, 'One');
INSERT INTO test_table (id, value) VALUES (2, 'Two');
COMMIT;
-- Create a unique index
CREATE UNIQUE INDEX test_table_uniq_idx ON test_table(id);
-- Create a non-unique index
CREATE INDEX test_table_idx ON test_table(id);
ORA-01408: such column list already indexed
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