Limiting amount of rows in OleDbDataAdapter query

Question

I am using C# and .NET 2.0. I created an OleDbDataAdapter to import a tab delimited file and in the SQL for one of my commands, I am adding 'LIMIT 1' to the end of the query.

string query = string.Format("SELECT DISTINCT * 
                                FROM {0} 
                              ORDER BY ZipCode 
                              LIMIT 1", tableName);

I run the query and my program throws an exception, System.Data.OleDb.OleDbException: Syntax error (missing operator) in query expression 'ZipCode LIMIT 1'.

I am just running some tests now but I'm curious as to why it does not work or if there is an alternate way to limit the amount of rows returned. I am working with files that have tens of thousands of rows and sometimes might need to limit the amount of rows returned.

Answer 1

As per my comment, the answer depends on the backend DB

For SQL Server you woult use TOP

string query = string.Format("SELECT DISTINCT TOP 1 *  
                              FROM {0}  
                              ORDER BY ZipCode", tableName);

For Oracle you would need to use ROWNUM in the where clause which queries against a sub-select. Something like this (untested)

string query = string.Format("SELECT * FROM (SELECT DISTINCT *  
                              FROM {0}  
                              ORDER BY ZipCode) where ROWNUM = 1", tableName);

And so on, depending on your backend DB.