T-SQL…表示法

Question

When researching ways to optimise bulk updates to SQL Server, I have come across the following query which works correctly but I'm having difficulty understanding how the '...' notation works in the following c# code snippet:

command.CommandText = "CREATE TABLE #TmpTable(...)";
command.ExecuteNonQuery();

command.CommandText = "UPDATE T SET ... FROM " + tableName + " T INNER JOIN #TmpTable Temp ON ...; DROP TABLE #TmpTable;"
command.ExecuteNonQuery();

Answer 1

There was a bug in the code so that the destination table was being updated directly instead of writing to the temporary table first. The referenced code was using the ellipsis (...) as a placeholder but for some reason my code failed to throw an exception where it should have done. The corrected snippet should read as follows:

command.CommandText = "CREATE TABLE #TmpTable(Id int, x int)";
command.ExecuteNonQuery();

// Insert updated rows read from 'tableName' into #TmpTable

command.CommandText = "UPDATE T SET T.x = Temp.x FROM " + tableName + " T INNER JOIN #TmpTable Temp ON T.Id = Temp.Id; DROP TABLE #TmpTable;"
command.ExecuteNonQuery();