[SQL]

场景：

使用 Oracle.DataAccess.dll 访问数据库时，OracleDataAdapter 执行失败。

异常：

System.AccessViolationException was unhandled
  HResult=-2147467261
  Message=Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
  Source=Oracle.DataAccess

分析：

有问题的SQL
select distinct username from user u, role r where u.roleid = r.id and u.id = 1

正确的SQL
select distinct u.username from user u, role r where u.roleid = r.id and u.id = 1

总结：

规范使用 SQL 语法，指定表别名进行联合查询。