mybatis 传入一个简单类型的参数，if判断的两种写法

1.使用注解

Integer countByKeyWord(@Param("keyWord") String keyWord);

<select id="countByKeyWord" resultType="int" parameterType="String">
select count(1) as total
from employee
where
<if test="keyword != null">
name = #{keyword}
</if>
</select>

2.使用_parameter

Integer countByKeyWord(String keyWord);

<select id="countByKeyWord" resultType="int" parameterType="String">
select count(1) as total
from employee
where
<if test="_parameter != null">
name = #{keyword}
</if>
</select>

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如果使用下面的写法，将会抛出异常：org.apache.ibatis.reflection.ReflectionException: There is no getter for property named 'keyWord' in 'class java.lang.String'

Integer countByKeyWord(String keyWord);

<select id="countByKeyWord" resultType="int" parameterType="String">
select count(1) as total
from employee
where
<if test="keyWord != null">
name = #{keyword}
</if>
</select>

关于 mybatis（_parameter） 的使用场景，可以参考：
http://openwares.net/database/mybatis_parametertype.html