1、动态SQL是一种可以根据不同条件生成不同SQL语句的技术，随着用户输入或外部条件变化而变化的SQL语句

2、SQL语句中的like模糊查询   xm like '%小米%'，但开发中经常用到 xm like concat("%",#{xm},"%")，可以防止sql注入

3、concat()函数用于将多个字符串连接成一个字符串

4、动态标签<if>:用于判断条件是否成立，使用test属性进行条件判断，如果条件为true，则拼接SQL

    IPage<JcCVo> selectByCyJddm(Page<JcCVo> page, @Param("xm")String xm,@Param("hjqx")String hjqx, @Param("zszldm") String zszldm, @Param("sfzhm")String sfzhm, @Param("jddm") String jddm, @Param("zszldmx") String zszldmx);

<select id="selectByCJddm" resultType="org.jeecg.modules.wlyg.vo.JcVo">SELECT *,CONCAT(LEFT(sfzhm,6),'********',RIGHT(sfzhm,4)) AS sfzhmbfrom jc_c where sfsc='N'<if test="hjqx == 'ws' ">AND  hjqx NOT LIKE '33%'  AND zszldm like 'S%'</if><if test="zszldm =='S1'">AND LEFT(zszldm, 2) LIKE 'S1'</if><if test="zszldm =='S0'">AND LEFT(zszldm, 2) LIKE 'S0'</if><if test="zszldmx != null and zszldmx != '' ">and zszldm = #{zszldmx}</if><if test="sfzhm != null and sfzhm != '' ">and sfzhm like concat("%",#{sfzhm},"%")</if><if test="jddm != null and jddm != '' ">and jddm = #{jddm}</if><if test="xm != null and xm != '' ">and xm like concat("%",#{xm},"%")</if>AND zszt='1'AND jddm is not nulland lbdm not like 'O%' and lbdm not like 'I%'</select>

5、动态标签<foreach>:一般用于批量操作，比如批量查询或删除

Integer getCynumberByZszl(@Param("ids") List<String> ids,@Param("flag") String flag);

foreach有几个属性：collection：遍历的集合        item：遍历出来的元素        separator：分割符        open：遍历开始前拼接的SQL片段        close：遍历结束后拼接的SQL片段

<select id="getCynumberByZszl" resultType="java.lang.Integer">SELECT count(*)FROM jc_cyzs swhere zszt='1'<if test="flag == 'zwcy' ">and s.zszldm LIKE 'S%' and s.zszldm != 'S000'</if><if test="flag == 'ptcy' ">and s.zszldm = 'S000'</if><if test="ids != null and ids != ''"><foreach collection="ids" item="id" open="and s.id in (" close=")" separator=",">#{id}</foreach></if></select>

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="org.jeecg.modules..mapper.Mapper"><select id="selectByCzId" resultType="org.jeecg.modules.wlyg.entity.Jc">select *from jc_cwhere id = #{czid}and sfsc = 'N'</select><select id="selectByCyJddm" resultType="org.jeecg.modules.wlyg.vo.Jc">SELECT *,CONCAT(LEFT(sfzhm,6),'********',RIGHT(sfzhm,4)) AS sfzhmbfrom jc_c where sfsc='N'<if test="hjqx == 'bq' ">AND hjqx like'330322'  AND zszldm like 'S%'</if><if test="hjqx == 'wq' ">AND hjqx NOT LIKE '330322' AND hjqx LIKE '33%'  AND zszldm like 'S%'</if><if test="hjqx == 'ws' ">AND  hjqx NOT LIKE '33%'  AND zszldm like 'S%'</if><if test="zszldm =='S1'">AND LEFT(zszldm, 2) LIKE 'S1'</if><if test="zszldm =='S2'">AND LEFT(zszldm, 2) LIKE 'S2'</if><if test="zszldm =='S5'">AND LEFT(zszldm, 2) LIKE 'S5'</if><if test="zszldm =='S0'">AND LEFT(zszldm, 2) LIKE 'S0'</if><if test="zszldmx != null and zszldmx != '' ">and zszldm = #{zszldmx}</if><if test="sfzhm != null and sfzhm != '' ">and sfzhm like concat("%",#{sfzhm},"%")</if><if test="jddm != null and jddm != '' ">and jddm = #{jddm}</if><if test="xm != null and xm != '' ">and xm like concat("%",#{xm},"%")</if>AND zszt='1'AND jddm is not nulland lbdm not like 'O%' and lbdm not like 'I%'</select><select id="getCynumberByZszl" resultType="java.lang.Integer">SELECT count(*)FROM jc_cyzs swhere zszt='1'<if test="flag == 'zwcy' ">and s.zszldm LIKE 'S%' and s.zszldm != 'S000'</if><if test="flag == 'ptcy' ">and s.zszldm = 'S000'</if><if test="ids != null and ids != ''"><foreach collection="ids" item="id" open="and s.id in (" close=")" separator=",">#{id}</foreach></if></select></mapper>