<1>
<select id="selectUserByConditions" parameterType="user" resultType="user">
SELECT * FROM USER WHERE 1=1
<if test="id != null and id!=''">
and id =#{id}
if>
<if test="id != null and id!=''">
id =#{id}
if>
<if test="email != null and email !=''">
and email =#{email}
if>
<if test="lastName != null and lastName !=''">
and last_name =#{lastName}
if>
<if test="gender == 1 or gender == 0">
and gender =#{gender}
if>
select>
<2>
<select id="selectUserByConditions" parameterType="user" resultType="user">
SELECT * FROM USER
<if test="gender == 1 or gender == 0">
gender =#{gender}
if>
-->
<where>
<if test="id != null and id!=''">
id =#{id}
if>
<if test="email != null and email !=''">
and email =#{email}
if>
<if test="lastName != null and lastName !=''">
and last_name =#{lastName}
if>
<if test="gender == 1 or gender == 0">
and gender =#{gender}
if>
where>
select>
<3>前后缀解决
后缀解决
<select id="selectUserByConditions" parameterType="user"
resultType="user">
SELECT * FROM USER
"where" suffixOverrides="and">
<if test="id != null and id!=''">
id =#{id} and
if>
<if test="email != null and email !=''">
email =#{email} and
if>
<if test="lastName != null and lastName !=''">
last_name =#{lastName} and
if>
<if test="gender == 1 or gender == 0">
gender =#{gender}
if>
select>
前缀解决
<select id="selectUserByCons" parameterType="user"
resultType="user">
SELECT * FROM USER
"where" prefixOverrides="and">
<if test="id != null and id!=''">
and id =#{id}
if>
<if test="email != null and email !=''">
and email =#{email}
if>
<if test="lastName != null and lastName !=''">
and last_name =#{lastName}
if>
<if test="gender == 1 or gender == 0">
and gender =#{gender}
if>
select>
<4>
<select id="selectUserByCons" parameterType="user"
resultType="user">
SELECT * FROM USER
<where>
<choose>
<when test="id != null and id!=''">
id =#{id}
"email != null and email !=''">
and email =#{email}
"lastName != null and lastName !=''">
and last_name =#{lastName}
<otherwise>
1=1
where>
select>
<5>更新
"updateUserById" parameterType="model.User">
UPDATE user
<set>
<if test="email != null and email !=''">
email =#{email},
if>
<if test="lastName != null and lastName !=''">
last_name =#{lastName},
if>
<if test="gender == 1 or gender == 0">
gender =#{gender}
if>
set>
WHERE id=#{id}
<6>批量查询
<select id="selectUserByIds" resultType="user">
SELECT * FROM USER where id
in
public List selectUserByIds(@Param("ids")List ids);对应collection="ids"
<foreach collection="list" item="item_id" open="(" separator=","
close=")">
#{item_id}
foreach>
select>
<7>批量保存
mysql下
//推荐使用
"addEmpsBatch">
INSERT INTO emp(ename,gender,email,did)
VALUES
<foreach collection="emps" item="emp" separator=",">
(#{emp.eName},#{emp.gender},#{emp.email},#{emp.dept.id})
foreach>
//在jdbc.url=jdbc:mysql://localhost:3306/mybatis?allowMultiQueries=true
批量batch保存mybatis ExecutorType.BATCH
Mybatis内置的ExecutorType有3种，默认为simple,该模式下它为每个语句的执行创建一个新的预处理语句，单条提交sql；而batch模式重复使用已经预处理的语句，并且批量执行所有更新语句，
显然batch性能将更优； 但batch模式也有自己的问题，比如在Insert操作时，在事务没有提交之前，是没有办法获取到自增的id，这在某型情形下是不符合业务要求的
Oracle下批量保存
方法1，将多个insert放在begin和end之间执行
begin
insert into user(userno,username,email) values (seq_user.nextval,'001','aaaaa');
insert into user(userno,username,email) values (seq_user.nextval,'002','bbbbbb');
end;
方法2利用中间表
insert into user(userno,username,email)
select seq_user.nextval,username,email from(
select '003' username ,'cccccc' email from dual
union
select '004' username,'ddddddddddd' email from dual
union
select '005' username,'eeeeeee' email from dual
)
-->
<insert id = "addUsers"databaseId="oracle" parameterType="user">
<foreach collection = "users" item="user" open="begin" close="end;">
insert into user(userno,username,email)
values (seq_user.nextval,#{user.username},#{user.email});
foreach>
insert into user(userno,username,email)
select seq_user.nextval,username,email from(
<foreach collection="users" item="user" separator="union" >
select #{user.username} username ,#{user.email} email from dual
foreach>
)
-->
<8>两个内置参数
<select id="selectUserByDataBaseId" resultType="user">
<bind name="nameLike" value="'%' + lastName + '%'"/>
<if test="_databaseId=='mysql'">
select * from user
<if test="_parameter!=null">
where last_name=#{_parameter.lastName}
if>
if>
<if test="_databaseId=='oracle'">
select * from user where last_name = #{nameLike}
if>
select>
<9>sql片段
"userColumn">
id,email,last_name,gender
<select id="selectUser" resultType="user">
select
"userColumn"/>
from user where id=#{id}
select>
2.
"userColumn">
id,email,last_name,gender,${AA}
<select id="selectUser" resultType="user">
select
"userColumn">
"AA" value="depart_id"/>
from user where id=#{id}
select>
