SQLite

  /* Test all UNIQUE constraints by creating entries for each UNIQUE
  ** index and making sure that duplicate entries do not already exist.
  ** Add the new records to the indices as we go.
  */
  for(iCur=0, pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext, iCur++){
    int regIdx;
    int regR;
    int addrSkipRow = 0;

    if( aRegIdx[iCur]==0 ) continue;  /* Skip unused indices */

    if( pIdx->pPartIdxWhere ){
      sqlite3VdbeAddOp2(v, OP_Null, 0, aRegIdx[iCur]);
      addrSkipRow = sqlite3VdbeMakeLabel(v);
      pParse->ckBase = regData;
      sqlite3ExprIfFalse(pParse, pIdx->pPartIdxWhere, addrSkipRow,
                         SQLITE_JUMPIFNULL);
      pParse->ckBase = 0;
    }

    /* Create a key for accessing the index entry */

    if( seenReplace ){
      if( onError==OE_Ignore ) onError = OE_Replace;
      else if( onError==OE_Fail ) onError = OE_Abort;
    }
    
    /* Check to see if the new index entry will be unique */
    regR = sqlite3GetTempReg(pParse);


    sqlite3VdbeAddOp2(v, OP_SCopy, regOldRowid, regR);
    j3 = sqlite3VdbeAddOp4Int(v, OP_IsUnique, baseCur+iCur+1, 0, regR, regIdx);
    sqlite3ReleaseTempRange(pParse, regIdx, pIdx->nKeyCol+1);

    /* Generate code that executes if the new index entry is not unique */
    assert( onError==OE_Rollback || onError==OE_Abort || onError==OE_Fail
        || onError==OE_Ignore || onError==OE_Replace );
    switch( onError ){
      case OE_Rollback:

        sqlite3GenerateRowDelete(
            pParse, pTab, pTrigger, baseCur, regR, 0, 0, OE_Replace
        );
        seenReplace = 1;
        break;
      }
    }
    sqlite3VdbeJumpHere(v, j3);
    sqlite3VdbeResolveLabel(v, addrSkipRow);
    sqlite3ReleaseTempReg(pParse, regR);
  }
  
  if( pbMayReplace ){
    *pbMayReplace = seenReplace;
  }

** This structure holds a record that has already been disassembled
** into its constituent fields.
*/
struct UnpackedRecord {
  KeyInfo *pKeyInfo;  /* Collation and sort-order information */
  u16 nField;         /* Number of entries in apMem[] */
  u8 flags;           /* Boolean settings.  UNPACKED_... below */
  i64 rowid;          /* Used by UNPACKED_PREFIX_SEARCH */
  Mem *aMem;          /* Values */
};

/*
** Allowed values of UnpackedRecord.flags
*/
#define UNPACKED_INCRKEY       0x01  /* Make this key an epsilon larger */
#define UNPACKED_PREFIX_MATCH  0x02  /* A prefix match is considered OK */
#define UNPACKED_PREFIX_SEARCH 0x04  /* Ignore final (rowid) field */

/*
** Each SQL index is represented in memory by an
** instance of the following structure.
**
** The columns of the table that are to be indexed are described
** by the aiColumn[] field of this structure.  For example, suppose

** If P4==0 then register P3 holds a blob constructed by MakeRecord.  If
** P4>0 then register P3 is the first of P4 registers that form an unpacked
** record.
**
** Cursor P1 is on an index btree.  If the record identified by P3 and P4
** is a prefix of any entry in P1 then a jump is made to P2 and
** P1 is left pointing at the matching entry.


*/
/* Opcode: NotFound P1 P2 P3 P4 *
**
** If P4==0 then register P3 holds a blob constructed by MakeRecord.  If
** P4>0 then register P3 is the first of P4 registers that form an unpacked
** record.
** 
** Cursor P1 is on an index btree.  If the record identified by P3 and P4
** is not the prefix of any entry in P1 then a jump is made to P2.  If P1 
** does contain an entry whose prefix matches the P3/P4 record then control
** falls through to the next instruction and P1 is left pointing at the
** matching entry.
**
** See also: Found, NotExists, IsUnique
*/



















case OP_NotFound:       /* jump, in3 */
case OP_Found: {        /* jump, in3 */
  int alreadyExists;

  VdbeCursor *pC;
  int res;
  char *pFree;
  UnpackedRecord *pIdxKey;
  UnpackedRecord r;
  char aTempRec[ROUND8(sizeof(UnpackedRecord)) + sizeof(Mem)*3 + 7];

#ifdef SQLITE_TEST
  sqlite3_found_count++;
#endif

  alreadyExists = 0;
  assert( pOp->p1>=0 && pOp->p1<p->nCursor );
  assert( pOp->p4type==P4_INT32 );
  pC = p->apCsr[pOp->p1];
  assert( pC!=0 );

          pC->pKeyInfo, aTempRec, sizeof(aTempRec), &pFree
      ); 
      if( pIdxKey==0 ) goto no_mem;
      assert( pIn3->flags & MEM_Blob );
      assert( (pIn3->flags & MEM_Zero)==0 );  /* zeroblobs already expanded */
      sqlite3VdbeRecordUnpack(pC->pKeyInfo, pIn3->n, pIn3->z, pIdxKey);
      pIdxKey->flags |= UNPACKED_PREFIX_MATCH;











    }
    rc = sqlite3BtreeMovetoUnpacked(pC->pCursor, pIdxKey, 0, 0, &res);
    if( pOp->p4.i==0 ){
      sqlite3DbFree(db, pFree);
    }
    if( rc!=SQLITE_OK ){
      break;
    }
    alreadyExists = (res==0);
    pC->nullRow = 1-alreadyExists;
    pC->deferredMoveto = 0;
    pC->cacheStatus = CACHE_STALE;
  }
  if( pOp->opcode==OP_Found ){
    if( alreadyExists ) pc = pOp->p2 - 1;
  }else{
    if( !alreadyExists ) pc = pOp->p2 - 1;
  }
  break;
}

/* Opcode: IsUnique P1 P2 P3 P4 *
**
** Cursor P1 is open on an index b-tree - that is to say, a btree which
** no data and where the key are records generated by OP_MakeRecord with
** the list field being the integer ROWID of the entry that the index
** entry refers to.
**
** The P3 register contains an integer record number. Call this record 
** number R. Register P4 is the first in a set of N contiguous registers
** that make up an unpacked index key that can be used with cursor P1.
** The value of N can be inferred from the cursor. N includes the rowid
** value appended to the end of the index record. This rowid value may
** or may not be the same as R.
**
** If any of the N registers beginning with register P4 contains a NULL
** value, jump immediately to P2.
**
** Otherwise, this instruction checks if cursor P1 contains an entry
** where the first (N-1) fields match but the rowid value at the end
** of the index entry is not R. If there is no such entry, control jumps
** to instruction P2. Otherwise, the rowid of the conflicting index
** entry is copied to register P3 and control falls through to the next
** instruction.
**
** See also: NotFound, NotExists, Found
*/
case OP_IsUnique: {        /* jump, in3 */
  u16 ii;
  VdbeCursor *pCx;
  BtCursor *pCrsr;
  u16 nField;
  Mem *aMx;
  UnpackedRecord r;                  /* B-Tree index search key */
  i64 R;                             /* Rowid stored in register P3 */

  pIn3 = &aMem[pOp->p3];
  aMx = &aMem[pOp->p4.i];
  /* Assert that the values of parameters P1 and P4 are in range. */
  assert( pOp->p4type==P4_INT32 );
  assert( pOp->p4.i>0 && pOp->p4.i<=(p->nMem-p->nCursor) );
  assert( pOp->p1>=0 && pOp->p1<p->nCursor );

  /* Find the index cursor. */
  pCx = p->apCsr[pOp->p1];
  assert( pCx->deferredMoveto==0 );
  pCx->seekResult = 0;
  pCx->cacheStatus = CACHE_STALE;
  pCrsr = pCx->pCursor;

  /* If any of the values are NULL, take the jump. */
  nField = pCx->pKeyInfo->nField;
  for(ii=0; ii<nField; ii++){
    if( aMx[ii].flags & MEM_Null ){
      pc = pOp->p2 - 1;
      pCrsr = 0;
      break;
    }
  }
  assert( (aMx[nField].flags & MEM_Null)==0 );

  if( pCrsr!=0 ){
    /* Populate the index search key. */
    r.pKeyInfo = pCx->pKeyInfo;
    r.nField = nField + 1;
    r.flags = UNPACKED_PREFIX_SEARCH;
    r.aMem = aMx;
#ifdef SQLITE_DEBUG
    { int i; for(i=0; i<r.nField; i++) assert( memIsValid(&r.aMem[i]) ); }
#endif

    /* Extract the value of R from register P3. */
    sqlite3VdbeMemIntegerify(pIn3);
    R = pIn3->u.i;

    /* Search the B-Tree index. If no conflicting record is found, jump
    ** to P2. Otherwise, copy the rowid of the conflicting record to
    ** register P3 and fall through to the next instruction.  */
    rc = sqlite3BtreeMovetoUnpacked(pCrsr, &r, 0, 0, &pCx->seekResult);
    if( (r.flags & UNPACKED_PREFIX_SEARCH) || r.rowid==R ){
      pc = pOp->p2 - 1;
    }else{
      pIn3->u.i = r.rowid;
    }
  }
  break;
}

/* Opcode: NotExists P1 P2 P3 * *
**
** P1 is the index of a cursor open on an SQL table btree (with integer
** keys).  P3 is an integer rowid.  If P1 does not contain a record with

    d1 += sqlite3VdbeSerialGet(&aKey1[d1], serial_type1, &mem1);

    /* Do the comparison
    */
    rc = sqlite3MemCompare(&mem1, &pPKey2->aMem[i], pKeyInfo->aColl[i]);
    if( rc!=0 ){
      assert( mem1.zMalloc==0 );  /* See comment below */

      /* Invert the result if we are using DESC sort order. */
      if( pKeyInfo->aSortOrder[i] ){
        rc = -rc;
      }
    
      /* If the PREFIX_SEARCH flag is set and all fields except the final
      ** rowid field were equal, then clear the PREFIX_SEARCH flag and set 
      ** pPKey2->rowid to the value of the rowid field in (pKey1, nKey1).
      ** This is used by the OP_IsUnique opcode.
      */
      if( (pPKey2->flags & UNPACKED_PREFIX_SEARCH) && i==(pPKey2->nField-1) ){
        assert( idx1==szHdr1 && rc );
        assert( mem1.flags & MEM_Int );
        pPKey2->flags &= ~UNPACKED_PREFIX_SEARCH;
        pPKey2->rowid = mem1.u.i;
      }
    
      return rc;
    }
    i++;
  }

  /* No memory allocation is ever used on mem1.  Prove this using
  ** the following assert().  If the assert() fails, it indicates a