Java整理22

1、动态sql

多条件查询	.xml配置文件中sql语句书写<select id="getEmpByCondition",resultType="Emp">select * from t_emp where <if test="empName != null and empName!=' ' ">empName=#{empName}</if><if test="age != null and age != ' ' "and age=#{age}</if></select>

2、where标签

<where><if                >and1 sex=#{sex} and2</if>
</where>
若where中无内容则where标签也不会生成where并且where标签会自动调节语句中的and是否出现，不过只能调节and1不能调节and2

3、Trim、Choose、When标签

当trim标签中有数据才会生效
属性prefix/suffix：将trim标签内容前/后添加指定内容
prefixOverrides/suffixOverrides：将trim标签内容前/后删除指定内容
<select id=" " resultTypde=" ">select * from t_user<where><choose><when> sex != null and sex != ' 'sex=#{sex}</when>......<othewise>id=1</otherwise></choose></where>
</select>

4、Foreach标签——批量删除

foreach标签
（1）in关键字<delete id=" ">delete from t_emp where eid in(_1<foreach collection="eids_集合或数组名" item="eid_元素" separator="," open="(_2",close=")_2" #{eid}</foreach>)_1</delete>(_1与(_2两个留一个即可
（2）where关键字<delete id=" ">delete from t_emp where <foreach collection=" " item=" " seperate="or" open="(" close=")" >eid=#{eid}</foreach></delete>

5、批量插入——sql标签

<insert id=" ">insert into t_emp values<foreach collection="emps" item="emp" separator=",">(null,#{emp.empName},#{emp.empSex})</foreach>
</insert>
sql标签<sql id="xxx">字段名1，字段名2</sql><select id="  " resultType=" ">select <include refid="xxx"></include> from t_emp <动态sql格式></select>