Question

How can i make a query with results sorted by a calculated column? (I can not pre calculate the result in other column to do the sorting!)

Example:

In a RDBMS tables like that:

TABLE products(
    product_id  INTEGER      NOT NULL,
    description VARCHAR(255) NOT NULL,
    price       DECIMAL(5,2) NOT NULL,
    qty         INTEGER      NOT NULL,
);

I can perform this query:

SELECT   product_id, (price * qty * {{current_tax}}) AS custom_calc
FROM     products
ORDER BY custom_calc DESC;

Im my problem i have a variable, in this case {{current_tax}}. In this way I can not pre calculate the result to do the sorting because the variable can change at any time.

there is an elegant solution to problems like this?

Tanks!

Answer 1

As you can see in the documentation, GQL does not support any arithmetic in the SELECT statement.

GQL is there as a convenience for people coming from SQL background, but the low level datastore API is much more like an indexed k/v store.

If current_tax is always a positive factor applied on price * qty it will not to modify the ordering anyway, so I would recommend storing price * qty as a new Product field, total_price and create a DESC index for it.