Mapper.xml映射文件：
 <select>  resultType如果返回的是集合，那么应该设置为集合包含的类型而不是集合本身的类型
如果参数类型是pojo类型，参数名必须是pojo中的属性名
<insert>
session.commit();
session = factory.openSession();

driver:com.mysql.jdbc.Driver
url:jdbc:mysql://127.0.0.1:3306/test
动态sql：
小于号
<![CDATA[<=]]>
:

<where>：
<if test="sal != null">
and sal <![CDATA[<=]]>#{sal}         //and，or会自动给去掉
</where>

choose when otherwise：
when otherwise中只走一个
select * from emp where
<choose><when test="sal != null">sal <![CDATA[<=]]> #{sal}</when><when test="ename != null">ename like concat('%',#{ename},'%')</when><otherwise>deptno=#{deptno}<otherwise>
</choose>

trim标签  组合 if标签 主要功能 可以在自己包含的内容前面加上某些前缀，也可以在其后加上某些后缀，与之对应的属性是prefix和suffix；
            可以把包含内容的首部某些内容覆盖，即忽略，也可以把尾部的某些内容覆盖，对应的属性是prefixOverrides和suffixOverrides

insert into emp
<trim prefix="("  suffix=")" suffixOverrides = ","><if test = "empno != null">empno,<if test = "ename != null">ename,<if test = "mgr != null">mgr,<if test = "sal != null">sal,<if test = "deptno != null">deptnol,
</trim>
values
<trim prefix="("  suffix=")" suffixOverrides = ","><if test = "empno !=null">#{empno},<if test = "ename != null">#{ename},<if test = "mgr != null">#{mgr},<if test = "sal != null">#{sal},<if test = "deptno != null">#{deptnol},
</trim>

<set>标签： 如果包含的语句以逗号结束会把逗号省略掉

update   emp
<set><if test="sal != null">sal=#{sal},</if><if test="mgr != null">mgr=#{mgr},</if><if test="ename != null">ename=#{ename},</if>
</set>
<where><if test="empno != null">and empno = #{empno}</if><if test="job != null">and job =  #{job}</if>
</where>

<foreach>主要用在构建in条件中，它可以在SQL语句中迭代一个集合
item 表示集合中每一个元素进行迭代时的别名
index指定一个名字，用于表示在迭代过程中，每次迭代到的位置
[LIST]:

select * from emp 
<where><foreach collection = "list" open = "(" close = ")" item="empno" seperator="or">empno=#{empno}</foreach>
</where>select * from emp where empno in <foreach collection = "list" open = "(" close = ")" item="empno" seperator=",">#{empno}</foreach>
</where>

[array]:
paramaterType = List

select * from emp where empno in <foreach collection = "array" open = "(" close = ")" item="empno" seperator=",">#{empno}</foreach>
</where>
[map]:

(Map<String,List<Integer> map>)
多条件复杂查询的时候
List<Emp> selectEmpByMapinfo(Map<String,object>)；

<select id = "selectEmpByMapinfo" paramaterType="java.util.Map" resultType="emp">select * from emp<where>deptno=#{deptnokey}andename like '%${enamekey}%'andempno in<foreach collection="empnos" open="(" close=")" separator="," item="no">#{no}</foreach></where>
</select>.

map.put("deptnokey",10)
map.put("enamekey","enamekey")
map.put(empnos,list)
[SQL片段]:

<sql id="sqlid">select * from emp
</sql>
<include refid="sqlid"></include>

[bind]标签

<select><bind name="name" value="'%' + ename + '%'">select * from emp<where><if test="sal != null">and sal <![CDATA[ <= ]]>#{sal]</if><if test="ename != null">and ename like #{name}</if></where>
</select>

resultType实现一对一 
多对多：

<collection property="ods" ofType="orderDetail" >
</collection>
<association property="items" javaType="items">
</association>

SqlSessionFactory factory;
Inputstream stream = Resources.getResourceasStream("SqlMapConfig.xml");
factory = SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder().build(stream)
 
page工具类实现分页：page工具类：
PageHelper.startPage((page- 1)* size,size)