title: ORA-01408: such column list already indexed
body: <p>Oracle SQL-Developer generates DDL statements of already exising database tables (items). It's quite strange that the generated DDL statements can't be applied within a new database instance. Here's a simplified example of the DDL</p>
  
  <pre><code>CREATE TABLE AB
    (
      "A"      NUMBER(*,0),
      "B"   NUMBER(*,0),
      "C" VARCHAR2(255 BYTE),
      CONSTRAINT "CHK_AB_A_NN" CHECK (A       IS NOT NULL) ENABLE,
      CONSTRAINT "CHK_AB_B_NN" CHECK (B       IS NOT NULL) ENABLE,
      CONSTRAINT "PK_AB" PRIMARY KEY ("A", "B")
    );
  CREATE INDEX "IDX_AB_A" ON "AB"("A");
  CREATE INDEX "IDX_AB_B" ON "AB"("B");
  CREATE UNIQUE INDEX "PK_AB" ON "AB"("A", "B");
  </code></pre>
  
  <p>If I execute those statements within a new oracle instance, I get the error: </p>
  
  <p><em><code>SQL-Fehler: ORA-01408: Diese Spaltenliste hat bereits einen Index
   1. 00000 -  "such column list already indexed"</code></em></p>
  
  <p>What's the reason for this error?</p>