trim标签&&MyBatis内置参数

SQL标签：<trim>

<where>可以处理拼接sql中 【开头】第一个and

<trim>可以处理拼接sql中 【开头或结尾】第一个and

开头：给拼接的sql加prefix="where" suffixOverrides="and"，处理拼接sql中开头第一个and

<select id="queryStudentByNoWithONGL" parameterType="student" resultType="student">
        select * from student1
        <trim prefix="where" prefixOverrides="and">
            <if test="stuName != null and stuName != '' ">
                and stuName like  '%${stuName}%'
            </if>
            <if test="graName != null and graName != '' ">
                and graName like  '%${graName}%'
            </if>
            <if test="stuAge != null and stuAge != '' ">
                and stuAge like  '%${stuAge}%'
            </if>
        </trim>
    </select>

 结尾

<select id="queryStudentByNoWithONGL" parameterType="student" resultType="student">
        select * from student1
        <trim prefix="where" suffixOverrides="and">
            <if test="stuName != null and stuName != '' ">
                stuName like  '%${stuName}%' and
            </if>
            <if test="graName != null and graName != '' ">
                graName like  '%${graName}%' and
            </if>
            <if test="stuAge != null and stuAge != '' ">
                stuAge =  #{stuAge} and
            </if>
        </trim>
    </select>

predix：拼接　　prefixOverrides：删除

内置参数:

　　_parameter：代表mybatis的输入参数

<select id="queryStudentByNoWithONGL" parameterType="student" resultType="student">
        /*select * from student1 where 1=1*/
        select * from student1
        <trim prefix="where" suffixOverrides="and">
            <if test="_parameter.stuName != null and _parameter.stuName != '' ">
                stuName like  '%${_parameter.stuName}%' and
            </if>
            <if test="graName != null and graName != '' ">
                graName like  '%${graName}%' and
            </if>
            <if test="stuAge != null and stuAge != '' ">
                stuAge =  #{stuAge} and
            </if>
        </trim>
    </select>

　　_datebaseId：代表当前数据库的名字