Does QueryToClass() support JOIN?

[bms]

This works OK:

private string SQLQuery = "SELECT Data_Manager.Time_Stamp, Inverter.RemoteReady FROM Data_Manager JOIN Inverter ON Inverter.Time_Stamp LIMIT 1000"   
private FieldHandle = DB.Query(MySQLHandle, SQLQuery)
? DB.Field(FieldHandle, 1)

But I get an error "O1004 Unable to run query" for this:

private string SQLQuery = "SELECT Data_Manager.Time_Stamp, Inverter.RemoteReady FROM Data_Manager JOIN Inverter ON Inverter.Time_Stamp LIMIT 1000"
private RO = DB.QueryToClass(MySQLHandle, SQLQuery) 
? RO.FieldNames

 

[AzeoTech]

That error comes from the database itself.  First you should try typing in the query directly into your database tool outside DAQFactory.  That will often give you a more detailed error message.  If it is successful, then the issue has to do with how DAQFactory does QueryToClass().  This function is designed for high efficiency acquisition of data from the database.  As such, it first queries for the number of records so it can preallocate the required memory.  It does this by replacing everything in the select with count(*), so:

select field1, field2 from myTable

would be replaced with

select count(*) from myTable

This works fine in most cases, but some more advanced queries, possibly like yours, it does not work with.  In these cases you are forced to use the older and slower db.Query() function and read records one at a time.