Q:

Azure Storage Table Query, Which is faster?

Very simple lookup, use A to lookup B, A is unique value in whole table, B is unique value in whole table as well
method 1:
PartionKey => A
RowKey => B

lookup by TOP(1) PartionKey eq "A"
method 2:
PartionKey => A
RowKey => "" (empty string)
Value => B

lookup by TOP(1)  (PartionKey eq "A") and (RowKey eq "")
method 3:
PartionKey => "" (empty string)
RowKey => A 
Value => B

lookup by TOP(1)  (PartionKey eq "") and (RowKey eq "A")
Question: Which is faster?

A:

In method #2, the row key is empty, but you're query specifies a non-empty row key (of "B"). Did you mean and (RowKey eq "")? If so, that method is faster, in that it will always return a result. Method #1 may return an empty result set with a continuation token, at which point you have to make a second query to actually get at the data.

