使用Mybatis框架时，涉及到的标签：
if标签 where标签 choose when otherwise标签 set标签 trim标签 bind标签 sql和include标签 foreach标签
1》if 标签
<if test="person != null and person != ‘‘">
AND rel.person=#{preson}
</if>
2》where 标签
功能：自动的给Sql语句添加where关键字，并将第一个and去除。
SELECT name FROM Person
<where> <if test="personId!= null and personId!= ‘‘"> AND rel.personId = #{personId} </if> <if test="meetType == ‘1‘.toString() "> AND rel.state in (‘1‘,‘2‘) </if> <if test="meetType == ‘2‘.toString() "> AND base.proj_stat_cd in (303,307) </if> <if test="meetType == ‘3‘.toString() "> AND base.proj_stat_cd in (309,404) </if> </where>
数据库执行时：SELECT name FROM Person where rel.personId = ‘id‘ and rel.state in (‘1‘,‘2‘)
3> choose when otherwise
<select id="queryPersonInfo" resultType="com.cctv.Person">
SELECT * from LOG
<where>
<choose>
<when test="param1!=null and param1!=‘‘">
and outno=#{param1}
</when>
<when test="param2!=null and param2!=‘‘">
and inno=#{param2}
</when>
<otherwise>
and 1=1
</otherwise>
</choose>
</where>
</select>
执行时，类似于java编译器解释执行
if（m == n）{
}else if(m > n){
}else{
}
4>.set标签
自动去除最后一个逗号。
注意: 在判断条件中最后保持有一个永远成立的条件。避免sql错误。
<update id="updatePersonInfo">
UPDATE Person
<set>
<if test="name != null and name !=‘‘">
name = #{name},
</if>
<if test="age !=null and age !=‘‘">
age =#{age},
</if>
<if test="weight !=null and weight !=‘‘">
weight=#{weight},
</if>
</set>
WHERE licenseId=#{licenseId}
</update>
数据库执行时：update person set name = "name", weight = "weight" WHERE licenseId = licenseId;
5>.trim 标签
prefix = "where" ：匹配成功的第一个 if 判断里的 sql片段前拼接 where ;
prefixOverrides = "and"：匹配成功的第一个if 判断里 sql 片段如果有 and ，将删除 and ；
suffix ，suffixOverrides 则是匹配最后一个；
顺序是 prefixOverrides -》prefix
<select id="selectUsersTrim" resultMap="resultListUsers" parameterType="Users">
select * from users
<trim prefix="where" prefixOverrides="and">
<if test="name!=null">
and name=#{name}
</if>
<if test="address!=null">
and address=#{address}
</if>
</trim>
</select>
链接：https://www.cnblogs.com/westward/p/6706570.html
6>.bing 标签
name : 参数名；
value ：表达式，< bind name = "score" value = "20+score" >
或 <bind name = "hostId" value = "‘$‘ + hostId">
<update id="updPerson" parameterType="com.ccav.Person">
<bind name="score" value="score+100"/>
update person
<trim prefix="set" suffixOverrides=",">
<if test="score !=null and score !=‘‘ ">
score = #{score},
</if>
</trim>
where personId =#{personId}
</update>
数据库执行时：score = 100， SQL = "update person score = 100 where personId = ‘id‘"；
7>.foreach 标签
collection ：要遍历的对象，类型：集合或数组；
item ：每次遍历的集合元素；
open ：在所拼接片段前拼接字符串；
separator ：多次遍历后拼接的内容之间的分割符；
close ：在所拼接片段最后追加字符串；
<if test=‘list != null and list.size() > 0‘>
<foreach item="item" collection="list" separator="or" index="" open="(" close=")">
(meeting.actl_meet_time = #{item.meetingTime} AND mes.corp_cn_fn = #{item.companyName})
</foreach>
</if>
执行时SQL片段：
(meeting.actl_meet_time = ‘time1‘ AND mes.corp_cn_fn = ‘name1‘)
or (meeting.actl_meet_time = ‘time2‘ AND mes.corp_cn_fn = ‘name2‘)
原文：https://www.cnblogs.com/unknownCode/p/13066319.html