Is there a way to see the raw SQL that a Sequel expression will generate?

Question

Say I have a Sequel expression like:

db.select(:id).from(:some_table).where(:foo => 5)

Is there a way to get the SQL string that this will generate (i.e. "SELECT id FROM some_table WHERE foo = 5")? I notice that calling inspect or to_s on the result of the above expression includes that generated SQL, but not sure how to access it directly.

And how about Sequel expressions that do not return a dataset, like:

db.from(:some_table).update(:foo => 5)

Is it possible to see the SQL from this before it's executed?

Gilbert

Answer 1

You can call sql on dataset:

db.select(:id).from(:some_table).where(:foo => 5).sql # => "SELECT `id` FROM `some_table` WHERE (`foo` = 5)"

For update queries you can do this:

db.from(:some_table).update_sql(:foo => 5) # => "UPDATE `some_table` SET `foo` = 5"

Some similar useful methods:

insert_sql
delete_sql
truncate_sql

Heaviside

What is db in this case and how do you access/instantiate it? – Quaff

Is there anyway to get at this from an ActiveRecord Relation? – Quaff

It's a Sequel connnection like db = Sequel.connect('sqlite://blog.db'). In ActiveRecord::Relation, you can just call to_sql – Heaviside

Thanks. :-) In the case of a particular Rails expression requiring multiple SQL statements to execute, do you know if .to_sql just gives the latest? – Quaff

Not sure what you mean. It will show you the statement related to the relation you call it on (it will show joins etc but not includes and preloads). – Heaviside

I'm not sure I know what I mean either, perhaps because I don't know what an include or preload is in this context. ;-) Is it sometimes necessary for Rails to execute a query in order to even construct a relation? I'm trying to understand the paragraphs starting with "Please note" at weblog.rubyonrails.org/2011/12/6/… – Quaff

Is there a known way to do this for distinct? For example db[:table].distinct(:id).sql and db[:table].distinct_sql(:id) don't work. – Cylinder