return getMask(pMaskSet, p->iTable);
mask = getMask(pMaskSet, p->iTable); if( mask==0 ) mask = -1; return mask;
static int exprTableUsage(ExprMaskSet *pMaskSet, Expr *p){  unsigned int mask = 0;  if( p==0 ) return 0;  if( p->op==TK_COLUMN ){    return getMask(pMaskSet, p->iTable);  }  if( p->pRight ){    mask = exprTableUsage(pMaskSet, p->pRight);  }  if( p->pLeft ){    mask |= exprTableUsage(pMaskSet, p->pLeft);  }  if( p->pList ){    int i;    for(i=0; i<p->pList->nExpr; i++){      mask |= exprTableUsage(pMaskSet, p->pList->a[i].pExpr);    }  }  return mask;}