SQLite

  /* Compute the comparison permutation and keyinfo that is used with
  ** the permutation used to determine if the next
  ** row of results comes from selectA or selectB.  Also add explicit
  ** collations to the ORDER BY clause terms so that when the subqueries
  ** to the right and the left are evaluated, they use the correct
  ** collation.
  */
  aPermute = sqlite3DbMallocRaw(db, sizeof(int)*(nOrderBy + 1));
  if( aPermute ){
    struct ExprList_item *pItem;
    aPermute[0] = nOrderBy;
    for(i=1, pItem=pOrderBy->a; i<=nOrderBy; i++, pItem++){
      assert( pItem->u.x.iOrderByCol>0 );
      assert( pItem->u.x.iOrderByCol<=p->pEList->nExpr );
      aPermute[i] = pItem->u.x.iOrderByCol - 1;
    }
    pKeyMerge = multiSelectOrderByKeyInfo(pParse, p, 1);
  }else{
    pKeyMerge = 0;

**
** Set the permutation used by the OP_Compare operator to be the array
** of integers in P4.
**
** The permutation is only valid until the next OP_Compare that has
** the OPFLAG_PERMUTE bit set in P5. Typically the OP_Permutation should 
** occur immediately prior to the OP_Compare.
**
** The first integer in the P4 integer array is the length of the array
** and does not become part of the permutation.
*/
case OP_Permutation: {
  assert( pOp->p4type==P4_INTARRAY );
  assert( pOp->p4.ai );
  aPermute = pOp->p4.ai + 1;
  break;
}

/* Opcode: Compare P1 P2 P3 P4 P5
** Synopsis: r[P1@P3] <-> r[P2@P3]
**
** Compare two vectors of registers in reg(P1)..reg(P1+P3-1) (call this

    case P4_VTAB: {
      sqlite3_vtab *pVtab = pOp->p4.pVtab->pVtab;
      sqlite3_snprintf(nTemp, zTemp, "vtab:%p", pVtab);
      break;
    }
#endif
    case P4_INTARRAY: {
      int i, j;
      int *ai = pOp->p4.ai;
      int n = ai[0];   /* The first element of an INTARRAY is always the
                       ** count of the number of elements to follow */
      zTemp[0] = '[';
      for(i=j=1; i<n && j<nTemp-7; i++){
        if( j>1 ) zTemp[j++] = ',';
        sqlite3_snprintf(nTemp-j, zTemp+j, "%d", ai[i]);
        j += sqlite3Strlen30(zTemp+j);
      }
      if( i<n ){
        memcpy(zTemp+j, ",...]", 6);
      }else{
        memcpy(zTemp+j, "]", 2);
      }
      break;
    }
    case P4_SUBPROGRAM: {
      sqlite3_snprintf(nTemp, zTemp, "program");
      break;
    }
    case P4_ADVANCE: {

** If the cursor is already pointing to the correct row and that row has
** not been deleted out from under the cursor, then this routine is a no-op.
*/
int sqlite3VdbeCursorMoveto(VdbeCursor **pp, int *piCol){
  VdbeCursor *p = *pp;
  if( p->eCurType==CURTYPE_BTREE ){
    if( p->deferredMoveto ){
      int iMap;
      if( p->aAltMap && (iMap = p->aAltMap[1+*piCol])>0 ){
        *pp = p->pAltCursor;
        *piCol = iMap - 1;
        return SQLITE_OK;
      }
      return handleDeferredMoveto(p);
    }
    if( sqlite3BtreeCursorHasMoved(p->uc.pCursor) ){
      return handleMovedCursor(p);
    }

  
  sqlite3VdbeAddOp3(v, OP_Seek, iCur, iRowid, iIdxCur);
  if( (pWInfo->wctrlFlags & WHERE_FORCE_TABLE)
   && sqlite3ParseToplevel(pParse)->writeMask==0 
  ){
    int i;
    Table *pTab = pIdx->pTable;
    int *ai = (int*)sqlite3DbMallocZero(pParse->db, sizeof(int)*(pTab->nCol+1));
    if( ai ){
      ai[0] = pTab->nCol;
      for(i=0; i<pIdx->nColumn-1; i++){
        assert( pIdx->aiColumn[i]<pTab->nCol );
        if( pIdx->aiColumn[i]>=0 ) ai[pIdx->aiColumn[i]+1] = i+1;
      }
      sqlite3VdbeChangeP4(v, -1, (char*)ai, P4_INTARRAY);
    }
  }
}

/*