postgresql - Postgres: How to get next item in an enum set? -


consider using code below. type enum_buysell includes 2 values: buy , sell. need opposite value in cases, code looks ugly, imho. there way optimise it? thought of not using enum @ all, e.g. make boolean instead, idea's not perfect makes data less obvious.

select   datetime,   case     when account_id_active  = p_account_id , direction = 'buy'  'buy'::enum_buysell     when account_id_active  = p_account_id , direction = 'sell' 'sell'::enum_buysell     when account_id_passive = p_account_id , direction = 'buy'  'sell'::enum_buysell     when account_id_passive = p_account_id , direction = 'sell' 'buy'::enum_buysell   end direction,   price,   volume   deals   account_id_active  = p_account_id or   account_id_passive = p_account_id order   datetime desc limit   10;

since there's no function getting next value of enum in postgresql, should define yourself.

create function next_buysell (e enum_buysell) returns enum_buysell $$ begin   return (case when e='buy'::enum_buysell 'sell'::enum_buysell                else 'buy'::enum_buysell           end); end $$ language plpgsql;

now, can use this:

postgres=# select next_buysell('sell'::enum_buysell);  next_buysell --------------  buy (1 row)  postgres=# select next_buysell('buy'::enum_buysell);  next_buysell --------------  sell (1 row)

and case statement becomes:

case   when account_id_active  = p_account_id direction   when account_id_passive = p_account_id next_buysell(direction) end direction

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