Append vs Append as new for performance

[Anonymous]

Would it improve performance if I appended one table to another "in place" (using append queries) vs creating a new table using "append as new"? I'm trying to append two tables: one is 50M rows while the other is 100K rows. When I use "append as new" it seems like its duplicating the loading of the table: once for the original table and once for the new combined table. It fails to load with the tables being that large, and I wanted to see if appending in place would solve this issue or if anyone had any insight on performance.

[v-yingjl]

Hi @Anonymous ,

You can use Query Diagnostics tool in power query to trace the performance.

Whether appending tables or appending tables as a new table, both of them use Table.combine() function. But seems like append tables directly work better based on the performance tracing.

append tables directlyappend tables directly

append as newappend as new

Best Regards,
Community Support Team _ Yingjie Li
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

[edhans · Accepted solution]

You first want to make sure if you are using Append as New, neither of the precedent queries are set to load. Right-click both and disable the "Enable Load" menu.

As for performance, should be no issue. The command is the same - Table.Combine, and the first argument is either the previous step (Append Query) or another query (Append as New). You should only use Append as New if you have some reason to re-use the query in the query you are starting the append from in another query for some reason. Otherwise are you are just making the Query Dependency View more complex by adding another query vs just making the existing query a few extra steps.