在执行缓慢的代码方面需要帮助 [英] need help with slow executing code

问题描述

我如何才能更有效地编写此代码，使其执行得更快?

How can I write this code more efficiently so it will execute faster?

DataTable dt1 = new DataTable();
dt1.Load(DbInfo.DataRdr(Conn, "SELECT DISTINCT     Events.Location FROM Events WHERE Events.Location NOT IN (SELECT Code FROM Locations)"));
  int cnt = 0;
  for (int i = 0; i < dt1.Rows.Count; i++)
  {
    Logging.Write(SetLength(" ", 10) + dt1.Rows[i]["Location"].ToString());
  }

---------------------
DbInfo.DataRdr返回一个SqlDataReader对象.

---------------------
DbInfo.DataRdr returns a SqlDataReader object.

推荐答案

这应该运行得更快一点

This should run a little faster

SqlDataReader reader = DbInfo.DataRdr(Conn, "SELECT DISTINCT Events.Location FROM Events WHERE 
NOT EXISTS( SELECT 1 FROM Location WHERE Code = Events.Location")
int colOrdinal = reader.GetOrdinal("Location");
while(reader.Read())
   {
   Logging.Write(SetLength(" ", 10) + reader.GetString(colOrdinal));
   }

如果您写5,000,000条记录，是的，这将非常慢.阅读本文，希望对您有所帮助.

left-outer-join-vs-not-exists1/ [^ ]

left-outer-join-vs-not-exists2 / [ ^ ]

If you write 5,000,000 records, yes it will be very slow. Read this, I hope it helps you.

left-outer-join-vs-not-exists1/[^]

left-outer-join-vs-not-exists2/[^]

在我看来，上面的代码是好的.

In my openion above code is good.

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