SSM查询不到数据,也不会报错,返回值为null
```xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace=绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.luo.dao.GoodsMapper">
<!--增-->
<insert id="addGoods" parameterType="com.luo.pojo.Goods">
insert into ssmexercise.goods (id,name,price,quantity)
values (#{id},#{name},#{price},#{quantity});
</insert>
<!--删-->
<delete id="deleteGoods" parameterType="com.luo.pojo.Goods">
delete from ssmexercise.goods where id=(#{id});
</delete>
<!-- 改-->
<update id="updateGoods" parameterType="com.luo.pojo.Goods">
update ssmexercise.goods
set name=#{name},price=#{price},quantity=#{quantity}
where id=#{id};
</update>
<!-- id查询-->
<select id="queryGoodsById" parameterType="Map" resultType="com.luo.pojo.Goods">
select * from ssmexercise.goods where id=#{id};
</select>
<!-- 全部查询-->
<select id="queryAllGoods" parameterType="java.lang.Integer" resultType="com.luo.pojo.Goods" >
select * from ssmexercise.goods;
</select>
</mapper>
```
```
检查数据库字段名
数据库能查出数据