一、if标签
<select id="queryEmpByCondition" resultType="User">
select * from t_user where 1=1
<if test="username != null and username != ''">
and username = #{username}
</if>
</select>@Test
public void test3(){
SqlSession sqlSession = SqlSessionUtils.sqlSession();
DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);
User admin = new User(null, "admin", null, null, null, null);
List<User> users = mapper.queryEmpByCondition(admin);
System.out.println(users);
}二、where标签
条件内容前的and或or
select id="queryEmpByCondition" resultType="User">
select * from t_user
<where>
<if test="username != null and username != ''">
and username = #{username}
</if>
</where>
</select>条件内容后的and或or
<select id="queryEmpByCondition" resultType="User">
select * from t_user
<where>
<if test="username != null and username != ''">
username = #{username} and
</if>
</where>
</select>三、trim标签
<select id="queryEmpByCondition" resultType="User">
select * from t_user
<trim prefix="where" suffixOverrides="and|or" >
<if test="username != null and username != ''">
username = #{username} and
</if>
</trim>
</select>四、choose、when、otherwise标签
<select id="queryEmpByCondition" resultType="User">
select * from t_user
<trim prefix="where" suffixOverrides="and|or" >
<choose>
<when test="username != null and username != ''">
username = #{username}
</when>
<when test="password != null and password != ''">
password = #{password}
</when>
<otherwise>
id = 1
</otherwise>
</choose>
</trim>
</select>五、foreach标签
批量删除：
形式一
<mapper namespace="com.cjc.ssm.mapper.DynamicSQLMapper">
<delete id="removeByUserArray">
delete from t_user where id in
<foreach collection="arr" item="id" separator="," open="(" close=")">
#{id}
</foreach>
</delete>形式二
<delete id="removeByUserArray">
delete from t_user where
<foreach collection="arr" item="id" separator="or">
id = #{id}
</foreach>
</delete>批量添加
<insert id="addUserList">
insert into t_user values
<foreach collection="list" item="user" separator=",">
(null,#{user.username},#{user.password},#{user.age},#{user.sex},#{user.email})
</foreach>
</insert>