动态SQL之sql标签(片段)

动态SQL之sql标签(片段)

• sql片段，可以记录一段公共sql片段，在使用的地方通过include标签进行引入

    <sql id="empColumns">
        emp_id,emp_name,age,gender,dept_id
    sql>

select <include refid="empColumns">include> from t_emp

MyBatis的映射文件DynamicSQLMapper.xml

"1.0" encoding="UTF-8" ?>
mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.atguigu.mybatis.mapper.DynamicSQLMapper">
 
    <sql id="empColumns">
        emp_id,emp_name,age,gender,dept_id
    sql>
 
    
    <select id="getEmpByCondition" resultType="Emp">
        select <include refid="empColumns">include> from t_emp
        <trim prefix="where" suffixOverrides="and">
            <if test="empName != null and empName != ''">
                emp_name = #{empName}
            if>
            <if test="age != null and age != ''">
                and age = #{age}
            if>
            <if test="gender != null and gender != ''">
                and gender = #{gender}
            if>
        trim>
    select>
mapper>