Postgresql在mybatis中报错:操作符不存在:character varying == unknown的问题

<div>
 <form:select path="finished" class="col-xs-12 form-control m-b">
 <form:option value="" label="请选择"/>
 <from:options items="${fns:getDictList('fin')}" itemLabel="label" 
  itemValue="value" htmlEscape="false"/>
 </form:select>
</div>

①
<if test="dSign!=null and dSign =='0'.toString()">
	AND (b.d_sign is null or b.d_sign='')
</if>
②
<if test="dSign!=null and dSign =='1'.toString()">
	AND (b.d_sign is not null AND b.d_sign!='')
</if>

select version(); //查询版本语句

alter table table_name rename to table_name2;

ALTER TABLE 表名 ALTER COLUMN 列名 SET DEFAULT 默认值; 

update table_name set fin=null; //正常完成修改操作

update table_name set fin is null; // 报语法错误！！！

update table_name set fin='0' where fin is null ; //正常完成修改操作

update table_name set fin='0' where fin = null ; //不报语法错误，但修改条数是0，不起修改作用

alter table 表名 alter COLUMN 列名 type varchar(255) ;

ALTER TABLE 表名 ADD 字段名 varchar(36);

//表中总共的记录数
select count(1) from table_name 32
 
select count(1) from table_name where d_sign is null 9 //32=9+23
select count(1) from table_name where d_sign is not null 23 //23=5+18
select count(1) from table_name where d_sign= '' 5
select count(1) from table_name where d_sign!='' 18
 
select count(1) from table_name where d_sign is null or d_sign='' 14 //32=14+18
select count(1) from table_name where d_sign is not null AND d_sign!='' 18