如果以防查询，Postgres嵌套

Question

Could you tell my why the following isnt working in postgres sql?:

See updated code below

UPDATE:

I expect the query to return "0.30" as float. This construct is only for testing purposes, i have some complex querys which depend on this conditional structure... BUt i dont know how to fix it..

Result is:

ERROR:  syntax error at or near "1"
LINE 4:     if 1=1 then

UPDATE:

This construction appears in a function... so I want to do following:

CREATE FUNCTION f_test(myvalue integer) RETURNS float AS $$
  BEGIN
    select (
      case (select '1')
      when '1' then
        if 1=1 then
          0.30::float
        else
          0.50::float
        end
      else
         1.00::float
      end
    );
  END;
$$ LANGUAGE plpgsql;

select f_test(1) as test;

Error message see above.

Answer 1

There is no IF expr THEN result ELSE result END syntax for normal SQL queries in Postgres. As there is neither an IF() function as in MySQL, you have to use CASE :

select (
  case (select '1')
  when '1' then
    case when 1=1 then 0.30::float else 0.50::float end
  else
     1.00::float
  end
);

Answer 2

I don't know what you're trying to achieve with this function, but here's a working version.

CREATE FUNCTION f_test(myvalue integer) RETURNS float AS $$
BEGIN
    IF myvalue = 1 THEN
            IF 1=1 THEN
                    RETURN 0.30::FLOAT;
            ELSE
                    RETURN 0.50::FLOAT;
            END IF;
    ELSE
            RETURN 1.0::FLOAT;
    END IF;
END;

The function returns 0.3 if input value is 1, otherwise it'll return 1. Edit: Note that 0.5 is never returned by the function.