Alternative notation for an empty SQL query condition O (￣▽￣) d

Simple description: Today look at the boss to submit the code, found an interesting thing, a SQL judge condition is empty, eldest brother's writing, let me before the light. Directly on the code

Code:

<select id= "Getxxxs" resultmap= "Xxxresultmap" parametertype= "String" >
    Select <include refid= "Field"/>from
    <include refid= "TableName" ></include>
    where r.xxx_level = ' 0 '
    <if test= "_parameter! = null and _parameter! =" ">
        and r.xxx_id! = #{_parameter}    //highlights are right here.   conditional judgment is not used in empty  statements again! Non-op  means r.xxx_id = null or = ' '
    </if>
</select>

Summary: In fact, this is not what to say, the key is a bit clever ah, record!!!

Alternative notation for an empty SQL query condition O (￣▽￣) d