SQLite

*/
static int indexIsUniqueNotNull(Index *pIdx, int nSkip){
  Table *pTab = pIdx->pTable;
  int i;
  if( pIdx->onError==OE_None ) return 0;
  for(i=nSkip; i<pIdx->nColumn; i++){
    int j = pIdx->aiColumn[i];
    assert( j>=0 && j<pTab->nCol );
    if( pTab->aCol[j].notNull==0 ) return 0;
  }
  return 1;
}

/*
** This function searches the expression list passed as the second argument
** for an expression of type TK_COLUMN that refers to the same column and

  int base,                       /* Cursor number for the table pIdx is on */
  ExprList *pDistinct,            /* The DISTINCT expressions */
  int nEqCol                      /* Number of index columns with == */
){
  Bitmask mask = 0;               /* Mask of unaccounted for pDistinct exprs */
  int i;                          /* Iterator variable */

  assert( pDistinct!=0 );
  if( pIdx->zName==0 || pDistinct->nExpr>=BMS ) return 0;
  testcase( pDistinct->nExpr==BMS-1 );

  /* Loop through all the expressions in the distinct list. If any of them
  ** are not simple column references, return early. Otherwise, test if the
  ** WHERE clause contains a "col=X" clause. If it does, the expression
  ** can be ignored. If it does not, and the column does not belong to the
  ** same table as index pIdx, return early. Finally, if there is no

    **    space to 1/16th of its original size (rangeDiv==16).
    **
    **  bSort:   
    **    Boolean. True if there is an ORDER BY clause that will require an 
    **    external sort (i.e. scanning the index being evaluated will not 
    **    correctly order records).
    **
    **  bDist:
    **    Boolean. True if there is a DISTINCT clause that will require an 
    **    external btree.
    **
    **  bLookup: 
    **    Boolean. True if a table lookup is required for each index entry
    **    visited.  In other words, true if this is not a covering index.
    **    This is always false for the rowid primary key index of a table.