Question

I need to do a query like this

select * from calendar where (select to_char(now(), 'day')) = true;

but this is invalid and fails with ERROR: failed to find conversion function from unknown to boolean.

The query I’m trying write, when run today would boil down to

select * from calendar where thursday = true;

But tomorrow, it should be

select * from calendar where friday = true;

The table has this schema

mbta=# \d calendar
             Table "public.calendar"
   Column   |          Type          | Modifiers 
------------+------------------------+-----------
 service_id | character varying(255) | not null
 monday     | boolean                | 
 tuesday    | boolean                | 
 wednesday  | boolean                | 
 thursday   | boolean                | 
 friday     | boolean                | 
 saturday   | boolean                | 
 sunday     | boolean                | 
 start_date | integer                | 
 end_date   | integer                | 

How can I write this query correctly?

Answer 1

That’s an ugly schema… A bunch of alternatives:

1. Replace ‘monday, tuesday… ‘ fields by a single integer field, to be interpreted as a bit mask – or use the bit-string data type

2. Replace them by a single field that contatins an array of integers (days of week).

3. Denormalize to an extra table, with a single day_of_week field and a FK to your calendar table.