SQLite

      break;
    }
    default: break;
  }
  return rc;
}










/*
** Return FALSE if there is no chance that the expression can be NULL.
**
** If the expression might be NULL or if the expression is too complex
** to tell return TRUE.  
**
** This routine is used as an optimization, to skip OP_IsNull opcodes

    ** a term of the form x=y does not prove that y is not null if x
    ** is the column of a virtual table */
    case TK_EQ:
    case TK_NE:
    case TK_LT:
    case TK_LE:
    case TK_GT:
    case TK_GE: {
      Expr *pLeft = pExpr->pLeft;
      Expr *pRight = pExpr->pRight;
      testcase( pExpr->op==TK_EQ );
      testcase( pExpr->op==TK_NE );
      testcase( pExpr->op==TK_LT );
      testcase( pExpr->op==TK_LE );
      testcase( pExpr->op==TK_GT );
      testcase( pExpr->op==TK_GE );
      /* The y.pTab=0 assignment in wherecode.c always happens after the
      ** impliesNotNullRow() test */
      if( (pLeft->op==TK_COLUMN && ALWAYS(pLeft->y.pTab!=0)
                               && IsVirtual(pLeft->y.pTab))
       || (pRight->op==TK_COLUMN && ALWAYS(pRight->y.pTab!=0)
                               && IsVirtual(pRight->y.pTab))
      ){
        return WRC_Prune;
      }
    }
    default:
      return WRC_Continue;
  }
}

/*
** Return true (non-zero) if expression p can only be true if at least

/*
** Test to see whether or not a table is a virtual table.  This is
** done as a macro so that it will be optimized out when virtual
** table support is omitted from the build.
*/
#ifndef SQLITE_OMIT_VIRTUALTABLE
#  define IsVirtual(X)      ((X)->nModuleArg)
#  define ExprIsVtab(X)  \
              ((X)->op==TK_COLUMN && (X)->y.pTab!=0 && (X)->y.pTab->nModuleArg)
#else
#  define IsVirtual(X)      0
#  define ExprIsVtab(X)     0
#endif

/*
** Macros to determine if a column is hidden.  IsOrdinaryHiddenColumn()
** only works for non-virtual tables (ordinary tables and views) and is
** always false unless SQLITE_ENABLE_HIDDEN_COLUMNS is defined.  The
** IsHiddenColumn() macro is general purpose.

int sqlite3ExprIsConstantOrFunction(Expr*, u8);
int sqlite3ExprIsConstantOrGroupBy(Parse*, Expr*, ExprList*);
int sqlite3ExprIsTableConstant(Expr*,int);
#ifdef SQLITE_ENABLE_CURSOR_HINTS
int sqlite3ExprContainsSubquery(Expr*);
#endif
int sqlite3ExprIsInteger(Expr*, int*);

int sqlite3ExprCanBeNull(const Expr*);
int sqlite3ExprNeedsNoAffinityChange(const Expr*, char);
int sqlite3IsRowid(const char*);
void sqlite3GenerateRowDelete(
    Parse*,Table*,Trigger*,int,int,int,i16,u8,u8,u8,int);
void sqlite3GenerateRowIndexDelete(Parse*, Table*, int, int, int*, int);
int sqlite3GenerateIndexKey(Parse*, Index*, int, int, int, int*,Index*,int);

    ** virtual table on their second argument, which is the same as
    ** the left-hand side operand in their in-fix form.
    **
    **       vtab_column MATCH expression
    **       MATCH(expression,vtab_column)
    */
    pCol = pList->a[1].pExpr;
    testcase( pCol->op==TK_COLUMN && pCol->y.pTab==0 );
    if( ExprIsVtab(pCol) ){
      for(i=0; i<ArraySize(aOp); i++){
        if( sqlite3StrICmp(pExpr->u.zToken, aOp[i].zOp)==0 ){
          *peOp2 = aOp[i].eOp2;
          *ppRight = pList->a[0].pExpr;
          *ppLeft = pCol;
          return 1;
        }

    **      OVERLOADED(vtab_column,expression)
    **
    ** Historically, xFindFunction expected to see lower-case function
    ** names.  But for this use case, xFindFunction is expected to deal
    ** with function names in an arbitrary case.
    */
    pCol = pList->a[0].pExpr;
    testcase( pCol->op==TK_COLUMN && pCol->y.pTab==0 );
    if( ExprIsVtab(pCol) ){
      sqlite3_vtab *pVtab;
      sqlite3_module *pMod;
      void (*xNotUsed)(sqlite3_context*,int,sqlite3_value**);
      void *pNotUsed;
      pVtab = sqlite3GetVTable(db, pCol->y.pTab)->pVtab;
      assert( pVtab!=0 );
      assert( pVtab->pModule!=0 );

        }
      }
    }
  }else if( pExpr->op==TK_NE || pExpr->op==TK_ISNOT || pExpr->op==TK_NOTNULL ){
    int res = 0;
    Expr *pLeft = pExpr->pLeft;
    Expr *pRight = pExpr->pRight;
    testcase( pLeft->op==TK_COLUMN && pLeft->y.pTab==0 );
    if( ExprIsVtab(pLeft) ){
      res++;
    }
    testcase( pRight && pRight->op==TK_COLUMN && pRight->y.pTab==0 );
    if( pRight && ExprIsVtab(pRight) ){
      res++;
      SWAP(Expr*, pLeft, pRight);
    }
    *ppLeft = pLeft;
    *ppRight = pRight;
    if( pExpr->op==TK_NE ) *peOp2 = SQLITE_INDEX_CONSTRAINT_NE;
    if( pExpr->op==TK_ISNOT ) *peOp2 = SQLITE_INDEX_CONSTRAINT_ISNOT;