myBatis --(5)动态sql
动态sql是myBatis中相当有用的一个知识点，总体来说，动态sql有如下几类：
1>if语句(简单的条件判断)
2>choose(相当于case when)，即C语言中的switth
3>trim(对包含的内容加上prefix(前缀)、或者suffix(后缀)等)
4>where(简化SQL语句中where条件判断)
5>set(用于 更新时设置)
6>foreach(实现myBatis in语句查询时有用)
如下例子均是普通sql操作的例子，如果采用oracle中的存储过程时，请直接看后面讲解。
一、if语句
使用环境举例：查询招聘列表，根据地点、薪资、工作经验等筛选条件进行筛选。
分析：这个时候，条件是动态的，可以全部选择，也可以只选择一部分。
动态SQL语句如下
<select id="getMyJobList" parameterType="com.zhiji.caren.VO.AttentionMyParams"
resultMap="BaseResultMapJobList">
SELECT
tall.LOCATION_ID,
tall.LOCATION_NAME,
tall.JOB_ID,
tall.JOB_NAME,
tall.NEGOTIABLE_FLAG,
tall.SALARY_MAX,
tall.SALARY_MIN,
tall.ADD_TIME,
tall.ENTERPRISE_ID,
tall.ENTERPRISE_NAME,
tall.ENTERPRISE_LOGO,
tall.WORK_YEARS_ID,
tall.WORK_YEARS_INFO,
IFNULL( tujf.FOCUS_FLAG,0) as
flag
FROM
(SELECT
tj.JOB_ID,
tj.LOCATION_ID,
tl.LOCATION_NAME,
tj.JOB_NAME,
tj.NEGOTIABLE_FLAG,
tj.SALARY_MAX,
tj.SALARY_MIN,
tj.ADD_TIME,
tj.ENTERPRISE_ID,
te.ENTERPRISE_NAME,
te.ENTERPRISE_LOGO,
twy.WORK_YEARS_ID,
twy.WORK_YEARS_INFO,
'' AS flag
FROM
t_job
tj,t_location tl,t_enterprise te,t_hr th,t_work_years
twy,t_job_category tjc,t_job_type tjt
WHERE tj.LOCATION_ID =
tl.LOCATION_ID
AND tl.LOCATION_LEVEL = 2
AND tl.USE_FLAG = 1
AND
tj.ENTERPRISE_ID = te.ENTERPRISE_ID
AND te.USE_FLAG = 1
AND tj.HR_ID =
th.HR_ID
AND th.USE_FLAG = 1
AND tj.WORK_YEARS_ID = twy.WORK_YEARS_ID
AND tj.JOB_CATEGORY_ID = tjc.JOB_CATEGORY_ID
AND tjc.USE_FLAG = 1
AND
tj.JOB_TYPE_ID = tjt.JOB_TYPE_ID
AND tjt.USE_FLAG = 1
<if test="jobCategoryId != null">
AND
tjc.JOB_CATEGORY_ID = #{jobCategoryId}
</if>
<if test="locationId != null">
AND
tl.LOCATION_ID = #{locationId}
</if>
<if test="workYearId != null">
AND
twy.WORK_YEARS_ID = #{workYearId}
</if>
<if test="jobTypeId != null">
AND
tjt.JOB_TYPE_ID = #{jobTypeId}
</if>
<if test="lastTime != null">
AND
tj.ADD_TIME <= #{lastTime}
</if>
GROUP BY
tj.JOB_ID
ORDER BY
tj.ADD_TIME DESC) tall
left join
(select JOB_ID
as
FOCUS_JOB_ID,'1' as FOCUS_FLAG from
t_user_job_focus where
user_id =
#{userId} and TYPE = '01') tujf
on
tall.JOB_ID = tujf.FOCUS_JOB_ID
LIMIT
#{pageIndex}
</select>
备注：很明显，上面的if判断可以满足需求，只有当输入的条件不为空时(即选择了该筛选条件)，SQL查询条件才带上这个筛选条件；否则，不带上这个筛选条件(即没有选择这个筛选条件)。
二、choose
它相当于C语言中的switch case。
适用场景：多选一的时候。
choose标签是按照顺序判断其内部when标签中的test条件是否成立，如果一旦成立，则choose语句结束；当choose中所有when条件都不满足时，则执行otherwise中的sql。
如上例子：筛选条件由多选变成单选
动态SQL语句如下
<select id="getMyJobList" parameterType="com.zhiji.caren.VO.AttentionMyParams"
resultMap="BaseResultMapJobList">
SELECT
tall.LOCATION_ID,
tall.LOCATION_NAME,
tall.JOB_ID,
tall.JOB_NAME,
tall.NEGOTIABLE_FLAG,
tall.SALARY_MAX,
tall.SALARY_MIN,
tall.ADD_TIME,
tall.ENTERPRISE_ID,
tall.ENTERPRISE_NAME,
tall.ENTERPRISE_LOGO,
tall.WORK_YEARS_ID,
tall.WORK_YEARS_INFO,
IFNULL( tujf.FOCUS_FLAG,0) as
flag
FROM
(SELECT
tj.JOB_ID,
tj.LOCATION_ID,
tl.LOCATION_NAME,
tj.JOB_NAME,
tj.NEGOTIABLE_FLAG,
tj.SALARY_MAX,
tj.SALARY_MIN,
tj.ADD_TIME,
tj.ENTERPRISE_ID,
te.ENTERPRISE_NAME,
te.ENTERPRISE_LOGO,
twy.WORK_YEARS_ID,
twy.WORK_YEARS_INFO,
'' AS flag
FROM
t_job
tj,t_location tl,t_enterprise te,t_hr th,t_work_years
twy,t_job_category tjc,t_job_type tjt
WHERE tj.LOCATION_ID =
tl.LOCATION_ID
AND tl.LOCATION_LEVEL = 2
AND tl.USE_FLAG = 1
AND
tj.ENTERPRISE_ID = te.ENTERPRISE_ID
AND te.USE_FLAG = 1
AND tj.HR_ID =
th.HR_ID
AND th.USE_FLAG = 1
AND tj.WORK_YEARS_ID = twy.WORK_YEARS_ID
AND tj.JOB_CATEGORY_ID = tjc.JOB_CATEGORY_ID
AND tjc.USE_FLAG = 1
AND
tj.JOB_TYPE_ID = tjt.JOB_TYPE_ID
AND tjt.USE_FLAG = 1
<choose>
<when test="jobCategoryId != null">
AND
tjc.JOB_CATEGORY_ID = #{jobCategoryId}
</when>
<when test="locationId != null">
AND
tl.LOCATION_ID = #{locationId}
</when>
<when test="workYearId != null">
AND
twy.WORK_YEARS_ID = #{workYearId}
</when>
<when test="jobTypeId != null">
AND
tjt.JOB_TYPE_ID = #{jobTypeId}
</when>
<when test="lastTime != null">
AND
tj.ADD_TIME <= #{lastTime}
</when>
<otherwise>
AND
1=1
</otherwise>
</choose>
GROUP BY
tj.JOB_ID
ORDER BY
tj.ADD_TIME DESC) tall
left join
(select JOB_ID
as
FOCUS_JOB_ID,'1' as FOCUS_FLAG from
t_user_job_focus where
user_id =
#{userId} and TYPE = '01') tujf
on
tall.JOB_ID = tujf.FOCUS_JOB_ID
LIMIT
#{pageIndex}
</select>
说明：上述的SQL语句完成 筛选条件 多选一的时候。即筛选条件始终是只能选择一个或者不选。
三、trim
这个一般用得很少，我举一段用代码生成器生成的例子，如下
<insert id="insertSelective" parameterType="com.zhiji.caren.model.Job">
insert into t_job
<trim prefix="(" suffix=")" suffixOverrides=",">
<if test="jobId != null">
JOB_ID,
</if>
<if test="jobName != null">
JOB_NAME,
</if>
<if test="jobTypeId != null">
JOB_TYPE_ID,
</if>
<if test="jobDepartment != null">
JOB_DEPARTMENT,
</if>
<if test="enterpriseId != null">
ENTERPRISE_ID,
</if>
<if test="jobCategoryId != null">
JOB_CATEGORY_ID,
</if>
<if test="salaryMin != null">
SALARY_MIN,
</if>
<if test="salaryMax != null">
SALARY_MAX,
</if>
<if test="locationId != null">
LOCATION_ID,
</if>
<if test="hrId != null">
HR_ID,
</if>
<if test="workYearsId != null">
WORK_YEARS_ID,
</if>
<if test="eduRequirementId != null">
EDU_REQUIREMENT_ID,
</if>
<if test="jobDescription != null">
JOB_DESCRIPTION,
</if>
<if test="jobAddress != null">
JOB_ADDRESS,
</if>
<if test="auditFlag != null">
AUDIT_FLAG,
</if>
<if test="stikyFlag != null">
STIKY_FLAG,
</if>
<if test="negotiableFlag != null">
NEGOTIABLE_FLAG,
</if>
<if test="hrInfoFlag != null">
HR_INFO_FLAG,
</if>
<if test="useFlag != null">
USE_FLAG,
</if>
<if test="validTime != null">
VALID_TIME,
</if>
<if test="updUserId != null">
UPD_USER_ID,
</if>
<if test="addTime != null">
ADD_TIME,
</if>
<if test="updTime != null">
UPD_TIME,
</if>
</trim>
<trim prefix="values (" suffix=")" suffixOverrides=",">
<if test="jobId != null">
#{jobId,jdbcType=INTEGER},
</if>
<if test="jobName != null">
#{jobName,jdbcType=VARCHAR},
</if>
<if test="jobTypeId != null">
#{jobTypeId,jdbcType=INTEGER},
</if>
<if test="jobDepartment != null">
#{jobDepartment,jdbcType=VARCHAR},
</if>
<if test="enterpriseId != null">
#{enterpriseId,jdbcType=INTEGER},
</if>
<if test="jobCategoryId != null">
#{jobCategoryId,jdbcType=INTEGER},
</if>
<if test="salaryMin != null">
#{salaryMin,jdbcType=INTEGER},
</if>
<if test="salaryMax != null">
#{salaryMax,jdbcType=INTEGER},
</if>
<if test="locationId != null">
#{locationId,jdbcType=INTEGER},
</if>
<if test="hrId != null">
#{hrId,jdbcType=INTEGER},
</if>
<if test="workYearsId != null">
#{workYearsId,jdbcType=INTEGER},
</if>
<if test="eduRequirementId != null">
#{eduRequirementId,jdbcType=INTEGER},
</if>
<if test="jobDescription != null">
#{jobDescription,jdbcType=VARCHAR},
</if>
<if test="jobAddress != null">
#{jobAddress,jdbcType=VARCHAR},
</if>
<if test="auditFlag != null">
#{auditFlag,jdbcType=CHAR},
</if>
<if test="stikyFlag != null">
#{stikyFlag,jdbcType=INTEGER},
</if>
<if test="negotiableFlag != null">
#{negotiableFlag,jdbcType=INTEGER},
</if>
<if test="hrInfoFlag != null">
#{hrInfoFlag,jdbcType=INTEGER},
</if>
<if test="useFlag != null">
#{useFlag,jdbcType=INTEGER},
</if>
<if test="validTime != null">
#{validTime,jdbcType=CHAR},
</if>
<if test="updUserId != null">
#{updUserId,jdbcType=INTEGER},
</if>
<if test="addTime != null">
#{addTime,jdbcType=CHAR},
</if>
<if test="updTime != null">
#{updTime,jdbcType=CHAR},
</if>
</trim>
</insert>
上述是一条insert语句，去掉动态标签部分，学过SQL的人都应该看得懂。
这段代码<trim prefix="(" suffix=")" suffixOverrides=",">解释如下：
从<trim prefix="(" suffix=")" suffixOverrides=",">开始，如下那段代码后缀遇到","时，将那段代码用()括起来，同时，去掉最后的那个","号。
中间这段代码<trim prefix="values (" suffix=")" suffixOverrides=",">解释如下：
从<trim prefix="values (" suffix=")" suffixOverrides=",">开始，如下那段代码后缀遇到","时，那段代码的前面加上 values (，后面用 ")"代替","。
四、where
直接看例子
<select id="getMyJobListPart" parameterType="com.zhiji.caren.VO.AttentionMyParams"
resultMap="BaseResultMapJobList">
SELECT
tallTwo.JOB_ID,
tallTwo.LOCATION_ID,
tallTwo.LOCATION_NAME,
tallTwo.JOB_NAME,
tallTwo.NEGOTIABLE_FLAG,
tallTwo.SALARY_MAX,
tallTwo.SALARY_MIN,
tallTwo.ADD_TIME,
tallTwo.ENTERPRISE_ID,
tallTwo.ENTERPRISE_NAME,
tallTwo.ENTERPRISE_LOGO,
tallTwo.WORK_YEARS_ID,
tallTwo.WORK_YEARS_INFO,
tallTwo.HR_ID,
tallTwo.JOB_CATEGORY_ID,
IFNULL( tujf.FOCUS_FLAG,0) as flag
FROM
(SELECT
tall.JOB_ID,
tall.LOCATION_ID,
tl.LOCATION_NAME,
tall.JOB_NAME,
tall.NEGOTIABLE_FLAG,
tall.SALARY_MAX,
tall.SALARY_MIN,
tall.ADD_TIME,
tall.ENTERPRISE_ID,
te.ENTERPRISE_NAME,
te.ENTERPRISE_LOGO,
tall.WORK_YEARS_ID,
twy.WORK_YEARS_INFO,
tall.HR_ID,
tall.JOB_CATEGORY_ID,
tall.JOB_TYPE_ID
FROM
(
SELECT
tj.JOB_ID,
tj.LOCATION_ID,
tj.JOB_NAME,
tj.NEGOTIABLE_FLAG,
tj.SALARY_MAX,
tj.SALARY_MIN,
tj.ADD_TIME,
tj.ENTERPRISE_ID,
tj.WORK_YEARS_ID,
tj.HR_ID,
tj.JOB_CATEGORY_ID,
tj.JOB_TYPE_ID
FROM
t_job tj
<if test="salaryId != null">
,t_salary ts
</if>
WHERE
1 = 1
<if test="salaryId != null">
AND ts.SALARY_ID = #{salaryId}
AND ts.SALARY_MAX
>=tj.SALARY_MAX
AND ts.SALARY_MIN <= tj.SALARY_MIN
</if>
<if test="locationId != null">
AND
tj.LOCATION_ID = #{locationId}
</if>
<if test="workYearId != null">
AND
tj.WORK_YEARS_ID = #{workYearId}
</if>
<if test="jobCategoryId != null">
AND
tj.JOB_CATEGORY_ID =
#{jobCategoryId}
</if>
<if test="jobTypeId != null">
AND
tj.JOB_TYPE_ID = #{jobTypeId}
</if>
<if test="lastTime != null">
AND
tj.ADD_TIME <= #{lastTime}
</if>
GROUP BY tj.JOB_ID
ORDER BY tj.ADD_TIME DESC
) tall
LEFT JOIN t_location
tl ON tall.LOCATION_ID = tl.LOCATION_ID
AND tl.LOCATION_LEVEL = 2
AND
tl.USE_FLAG = 1
LEFT JOIN t_enterprise te ON tall.ENTERPRISE_ID =
te.ENTERPRISE_ID
AND te.USE_FLAG = 1
LEFT JOIN t_hr th ON tall.HR_ID =
th.HR_ID
AND th.USE_FLAG = 1
LEFT JOIN t_work_years twy ON
tall.WORK_YEARS_ID = twy.WORK_YEARS_ID
LEFT JOIN t_job_category tjc ON
tall.JOB_CATEGORY_ID = tjc.JOB_CATEGORY_ID
AND tjc.USE_FLAG = 1
LEFT JOIN t_job_type tjt ON
tall.JOB_TYPE_ID = tjt.JOB_TYPE_ID
AND tjt.USE_FLAG = 1)
tallTwo
LEFT JOIN (select JOB_ID as FOCUS_JOB_ID,'1' as FOCUS_FLAG from
t_user_job_focus where user_id = #{userId} and TYPE = '01') tujf
ON
tallTwo.JOB_ID = tujf.FOCUS_JOB_ID
LIMIT #{pageIndex}
</select>
如上动态SQL中有一个 where 1=1的地方，原本的情况应该写成这样
WHERE
<if test="salaryId != null">
ts.SALARY_ID = #{salaryId}
AND ts.SALARY_MAX
>=tj.SALARY_MAX
AND ts.SALARY_MIN <= tj.SALARY_MIN
</if>
原本的情况下 当salaryId无值时，就会出现问题。改用where标签修改成如下：
tj.JOB_CATEGORY_ID,
tj.JOB_TYPE_ID
FROM
t_job tj
<if test="salaryId != null">
,t_salary ts
</if>
<where>
<if test="salaryId != null">
ts.SALARY_ID = #{salaryId}
AND ts.SALARY_MAX
>=tj.SALARY_MAX
AND ts.SALARY_MIN <= tj.SALARY_MIN
</if>
......
</where>
GROUP BY tj.JOB_ID
......
说明：这种写法是 当<where>后的判断语句中有一条成立时，会在成立的语句之前加上where；如果成立的语句之前有AND或者OR，则mybatis会自动的去掉AND或OR。
五、set
主要是在update语句时使用
如下是我用代码生成器生成的一段代码如下
<update id="updateByPrimaryKeySelective" parameterType="com.zhiji.caren.model.Job">
update t_job
<set>
<if test="jobName != null">
JOB_NAME = #{jobName,jdbcType=VARCHAR},
</if>
<if test="jobTypeId != null">
JOB_TYPE_ID = #{jobTypeId,jdbcType=INTEGER},
</if>
<if test="jobDepartment != null">
JOB_DEPARTMENT = #{jobDepartment,jdbcType=VARCHAR},
</if>
<if test="enterpriseId != null">
ENTERPRISE_ID = #{enterpriseId,jdbcType=INTEGER},
</if>
<if test="jobCategoryId != null">
JOB_CATEGORY_ID = #{jobCategoryId,jdbcType=INTEGER},
</if>
<if test="salaryMin != null">
SALARY_MIN = #{salaryMin,jdbcType=INTEGER},
</if>
<if test="salaryMax != null">
SALARY_MAX = #{salaryMax,jdbcType=INTEGER},
</if>
<if test="locationId != null">
LOCATION_ID = #{locationId,jdbcType=INTEGER},
</if>
<if test="hrId != null">
HR_ID = #{hrId,jdbcType=INTEGER},
</if>
<if test="workYearsId != null">
WORK_YEARS_ID = #{workYearsId,jdbcType=INTEGER},
</if>
<if test="eduRequirementId != null">
EDU_REQUIREMENT_ID =
#{eduRequirementId,jdbcType=INTEGER},
</if>
<if test="jobDescription != null">
JOB_DESCRIPTION = #{jobDescription,jdbcType=VARCHAR},
</if>
<if test="jobAddress != null">
JOB_ADDRESS = #{jobAddress,jdbcType=VARCHAR},
</if>
<if test="auditFlag != null">
AUDIT_FLAG = #{auditFlag,jdbcType=CHAR},
</if>
<if test="stikyFlag != null">
STIKY_FLAG = #{stikyFlag,jdbcType=INTEGER},
</if>
<if test="negotiableFlag != null">
NEGOTIABLE_FLAG = #{negotiableFlag,jdbcType=INTEGER},
</if>
<if test="hrInfoFlag != null">
HR_INFO_FLAG = #{hrInfoFlag,jdbcType=INTEGER},
</if>
<if test="useFlag != null">
USE_FLAG = #{useFlag,jdbcType=INTEGER},
</if>
<if test="validTime != null">
VALID_TIME = #{validTime,jdbcType=CHAR},
</if>
<if test="updUserId != null">
UPD_USER_ID = #{updUserId,jdbcType=INTEGER},
</if>
<if test="addTime != null">
ADD_TIME = #{addTime,jdbcType=CHAR},
</if>
<if test="updTime != null">
UPD_TIME = #{updTime,jdbcType=CHAR},
</if>
</set>
where JOB_ID = #{jobId,jdbcType=INTEGER}
</update>
看得懂纯SQL的人应该能看懂如上代码，<set>标签的作用主要是在中间那段代码的前面加上 set。如下是我没有使用<set>标签的更新语句，阅读者对比看下就能懂了。
<update id="updateByPrimaryKey" parameterType="com.zhiji.caren.model.Job">
update t_job
set
JOB_NAME = #{jobName,jdbcType=VARCHAR},
JOB_TYPE_ID =
#{jobTypeId,jdbcType=INTEGER},
JOB_DEPARTMENT =
#{jobDepartment,jdbcType=VARCHAR},
ENTERPRISE_ID =
#{enterpriseId,jdbcType=INTEGER},
JOB_CATEGORY_ID =
#{jobCategoryId,jdbcType=INTEGER},
SALARY_MIN =
#{salaryMin,jdbcType=INTEGER},
SALARY_MAX =
#{salaryMax,jdbcType=INTEGER},
LOCATION_ID =
#{locationId,jdbcType=INTEGER},
HR_ID = #{hrId,jdbcType=INTEGER},
WORK_YEARS_ID = #{workYearsId,jdbcType=INTEGER},
EDU_REQUIREMENT_ID =
#{eduRequirementId,jdbcType=INTEGER},
JOB_DESCRIPTION =
#{jobDescription,jdbcType=VARCHAR},
JOB_ADDRESS =
#{jobAddress,jdbcType=VARCHAR},
AUDIT_FLAG =
#{auditFlag,jdbcType=CHAR},
STIKY_FLAG = #{stikyFlag,jdbcType=INTEGER},
NEGOTIABLE_FLAG = #{negotiableFlag,jdbcType=INTEGER},
HR_INFO_FLAG =
#{hrInfoFlag,jdbcType=INTEGER},
USE_FLAG = #{useFlag,jdbcType=INTEGER},
VALID_TIME = #{validTime,jdbcType=CHAR},
UPD_USER_ID =
#{updUserId,jdbcType=INTEGER},
ADD_TIME = #{addTime,jdbcType=CHAR},
UPD_TIME = #{updTime,jdbcType=CHAR}
where JOB_ID =
#{jobId,jdbcType=INTEGER}
</update>
六、foreach
我用得比较少，这里不赘述，有需要的朋友可以参考如下地址
http://haohaoxuexi.iteye.com/blog/1338557