title: Oracle: ORA-01408: such column list already indexed
body: <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>