如何将mysql if基于条件的值插入转换为postgresql

上面的查询是基于param值为market_fk插入值，它在MySQL中工作。如何将上述查询转换为postgresql？

使用

插入。。。选择

：

insert into agreement_form 
  set created = now(), 
      market_fk = (if (? = '''', null, (select m.id from market m where m.name = ?)))

insert into agreement_form (created, market_fk)
select now(), 
       case  
          when ? = '''' then null
          else (select m.id from market m where m.name = ?)
       end;