mybatis动态插入sql语句

if标签

1. if标签就类似于jstl的if标签

where标签

1. 在执行多条件选择时，可能会多出一个and 关键字。譬如：

    <select id="getEmpAndDep"  resultType="emp" databaseId="mysql"> 
   select last_name,email,id,gender from employee 
   where
   <if test="id!=null">
    id=#{id}
   if>
     <if test="lastName!=null and lastName!=''">
      and last_name like #{lastName}
   if>
    <if test="gender==0 or gender==1">
      and gender=#{gender}
   if>
    <if test="email!=null and email.trim()!=''">
      and email=#{email}
   if>
    select> 

1. 那么，当id=null时候，拼接的语句就会多出来一个and。
2. where标签可以删除多余的前缀and /or，然后加上where
3. 将动态语句嵌入where标签中即可

 <where>
   <if test="id!=null">
    id=#{id}
   if>
     <if test="lastName!=null and lastName!=''">
      or last_name like #{lastName}
   if>
    <if test="gender==0 or gender==1">
      and gender=#{gender}
   if>
    <if test="email!=null and email.trim()!=''">
      and email=#{email}
   if>
   where>

set标签

1. 和where用法差不多，在执行更新语句时，可能会多余一个逗号。
2. 用于替代set关键字，用法如下

    <set>
     <if test="lastName!=null">
        last_Name=#{lastName},
     if>
     <if test="email!=null">
        email=#{email},
     if>
     <if test="gender!=null">
         gender=#{gender}
     if>
    set>

trim标签

<trim prefix="set" suffixOverrides=",">trim>

1. 在语句前插入prefix指明的前缀，suffixOverrides 是对末尾指明的多余的符号清除。
2. 可以用来代替set标签和where标签

<trim prefix="WHERE" prefixOverrides="and">trim>

choose 标签

<update id="updateEmp"  >
        update employee 
        <set>
        <choose>
            <when test="lastName!=null">
                   last_Name=#{lastName},       
            when>
            <when test="email!=null">
                   email=#{email},      
            when>
            <when test="gender!=null">
                    gender=#{gender},       
            when>
            <otherwise>
                gender=1    
            otherwise>
        choose>
        set>
      where id=#{id}
    update>

1. 类似于elseif 或者switch case语句
2. 一旦一个匹配上，其余的便不再执行。

foreach标签

1. collection 指定要遍历的集合，list类型的参数会特殊处理封装在map中，key就叫list
2. item 将当前遍历出的元素赋值给指定的变量
3. separator 每个元素之间的分隔符
4. open 在遍历出所有的结果之后拼接一个开始的字符串
5. close 遍历出所有的结果后拼接一个结束的字符
6. index 索引 遍历list 的时候是索引，遍历map的时候是map的key，item即为当前项的值。

用来批量查询

查询语句：select * from employee where id in (1,2,3);

  <select id="getByIterator" resultType="emp">
  select * from employee where id in
  <foreach collection="map" item="item" open="(" close=")" separator=",">
   #{item}
  foreach>
  select>

用来批量插入

1. 第一种，利用values
2. 第二种，同一行执行多条sql插入语句。需要在连接参数上进行配置。

jdbc.url=jdbc:mysql://localhost:3306/mybatis?allowMultiQueries=true&&useUnicode=true&&characterEncoding=utf8

 第一种："BatchInsert" >
    insert into employee (last_name,email,gender)Values
    <foreach collection="list" item="item" separator=",">
      (#{item.lastName},#{item.email},#{item.gender})
    foreach>      
  

第二种
"BatchInsert2" >
   <foreach collection="list" item="item" separator=";">
    insert into employee (last_name,email,gender)Values
      (#{item.lastName},#{item.email},#{item.gender})
    foreach>      
  

oracle环境下多条记录插入

1. 在begin 和 end 间写入多条插入语句
2. 利用中间表

sql语句
begin
    insert into employee (last_name,email,gender)
    Values ("hou","[email protected]",1);
    insert into employee (last_name,email,gender)
    Values ("hou","[email protected]",1);
end;    

foreach代码
"BatchInsert2" >
   <foreach collection="list" item="item" open="begin" close="end">
    insert into employee (id,last_name,email,gender)Values
      (employee_seq.nextval,#{item.lastName},#{item.email},#{item.gender})
    foreach>      
  

insert into employee (id,last_name,gender,email) 
select employeeseq.nextval,last_name,gender,email from(
select  "[email protected]" email,"hou" last_name,0 gender from dual union
select  "[email protected]" email,"hou" last_name,0 gender from dual 
)

foreach语句
"BatchInsert2" >
insert into employee (id,last_name,gender,email) 
select employee_seq.nextval,last_name,gender,email from(
 <foreach collection="list" item="item" separator="union">
    select #{item.lastName} last_name,#{item.email} email,#{item.gender} gender
 foreach>