Oracle: ORA-01408: such column list already indexed
<p>I have created a table: </p>

<pre><code>CREATE TABLE SCHEMA_NAME.TABLE_NAME
(
  ID VARCHAR2(100) PRIMARY KEY NOT NULL,
  A_ID VARCHAR2(100) NOT NULL,
  B_ID VARCHAR2(100),
  C_ID INTEGER,
  CONSTRAINT FK_C_NOTE FOREIGN KEY (C_ID) REFERENCES C(ID),
  CONSTRAINT FK_A_NOTE FOREIGN KEY (A_ID) REFERENCES A(ID),
  CONSTRAINT FK_B_NOTE FOREIGN KEY (B_ID) REFERENCES B(ID)
);
</code></pre>

<p>And I have tried to apply the following indexes:</p>

<pre><code>CREATE INDEX IDX_FK_A_TABLE_NAME on SCHEMA_NAME.TABLE_NAME(A_ID) tablespace TS_SCHEMA_NAME_DATA;
CREATE INDEX IDX_FK_C_TABLE_NAME on SCHEMA_NAME.TABLE_NAME(C_ID) tablespace TS_SCHEMA_NAME_DATA; --Fails
CREATE INDEX IDX_FK_B_TABLE_NAME on SCHEMA_NAME.TABLE_NAME (B_ID) tablespace TS_SCHEMA_NAME_DATA; --Fails
</code></pre>

<p>But when I try to create the last two indexes I get:</p>

<blockquote>
  <p>ORA-01408: such column list already indexed</p>
</blockquote>

<p>Why is this? Are these indexes created automatically?</p>

<hr>

<p>If I try: </p>

<pre><code>SELECT INDEX_NAME FROM ALL_INDEXES WHERE TABLE_NAME = 'NOTE';
</code></pre>

<p>I get:</p>

<pre><code>INDEX_NAME
----------
IDX_FK_A_TABLE_NAME
SYS_C0044692561
</code></pre>