How does dplyr decide when to combine multiple mutate statements?

[Jarod G.R. Meng]

When I use dplyr on local data frames, I love the feature whereby mutate can refer to columns that I just created. However, when I use dplyr to translate the verbs into SQL, this feature can be problematic because databases usually don't support reference to newly-created columns. The workaround is to create layered subqueries, so I naturally tried to split my mutate statements and artificially create subqueries. Unfortunately dplyr seems to be automatically combining my multiple mutate statements when translating into SQL. Is there a way to ask dplyr *not* to combine multiple mutate statements (in other words, forcing dplyr to create individual subqueries)?

Thanks.

[Genrong MENG]

I boiled this down to the mutate_.tbl_sql function which only creates a subquery when window functions are used. Is it possible to add an argument to control the collapsing behavior so that users can choose when to create a subquery rather than just append the select statements?

On Tue, Jul 21, 2015 at 9:54 PM, Jarod G.R. Meng <genron...@gmail.com> wrote:

When I use dplyr on local data frames, I love the feature whereby mutate can refer to columns that I just created. However, when I use dplyr to translate the verbs into SQL, this feature can be problematic because databases usually don't support reference to newly-created columns. The workaround is to create layered subqueries, so I naturally tried to split my mutate statements and artificially create subqueries. Unfortunately dplyr seems to be automatically combining my multiple mutate statements when translating into SQL. Is there a way to ask dplyr *not* to combine multiple mutate statements (in other words, forcing dplyr to create individual subqueries)?

Thanks.

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[Hadley Wickham]

I'd rather just fix the bug than adding a new syntax. In the mean
time you can use collapse() to force subquery creation.
Hadley

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