postgresql如何兼容MySQL if函数

create or replace function if(bln boolean,inValue1 anyelement,inValue2 anyelement)
returns anyelement as
$$
begin
if bln=true then
   return inValue1;
else
   return inValue2;
end if;
end;
$$
language plpgsql;

create or replace function if(bln boolean,inValue1 numeric,inValue2 numeric)
returns numeric as
$$
begin
if bln=true then
   return inValue1;
else
   return inValue2;
end if;
end;
$$
language plpgsql;

create or replace function if(bln boolean,inValue1 numeric,inValue2 text)
returns text as
$$
begin
if bln=true then
   return inValue1;
else
   return inValue2;
end if;
end;
$$
language plpgsql;

select (select * from table_name where age = 20) t from dual

select (select * from table_name where age = 20) t

update table_name t set t.name = 'abc' where id = 1

select * from table_name where name = 'abc'

select * from table_name where name = "abc"

insert into table_name() values()

insert all into table_name() values()

<insert id="insertBatch" parameterType="java.util.List">
  <if test="_databaseId=='mysql' or _databaseId=='postgresql'">
    insert into table_name
    (<include refid="insertBatchColumn"></include>)
    values
    <foreach collection="list" item="item" index="index" separator="," >
      (<include refid="insertBatchValue"></include>)
    </foreach>
  </if>
  <if test="_databaseId=='oracle'">
    insert all
    <foreach collection="list" item="item" index="index" separator="">
      into table_name
      (<include refid="insertBatchColumn"></include>)
      values (<include refid="insertBatchValue"></include>)
    </foreach>
    select * from dual
  </if>
</insert>

<sql id="insertBatchColumn">
  id,name,age,gender
</sql>
<sql id="insertBatchValue">
  #{item.id,jdbcType=VARCHAR}, #{item.name,jdbcType=VARCHAR},
  #{item.age,jdbcType=INTEGER},#{item.gender,jdbcType=INTEGER}
</sql>