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mybatis性能优化二之多对多查询:用一次请求解决n次请求查询
&resultMap type="com.cn.vo.Teacher" id="teacher"&
&id property="id" column="id" javaType="int" jdbcType="INTEGER" /&
&result property="name" column="name" javaType="string"
jdbcType="VARCHAR" /&
&collection property="students" column="t_s_id" ofType="com.cn.vo.Student"&
&id property="sid" column="sid" javaType="int" jdbcType="INTEGER" /&
&result property="sname" column="sname" javaType="string"
jdbcType="VARCHAR" /&
&/collection& --&
&collection property="students" resultMap="studentResultMap" /&
&collection property="goods" resultMap="goodsResultMap" /&
&/resultMap&
&resultMap type="com.cn.vo.Student" id="studentResultMap"&
&id property="sid" column="sid" javaType="int" jdbcType="INTEGER" /&
&result property="sname" column="sname" javaType="string" jdbcType="VARCHAR" /&
&/resultMap&
&resultMap type="com.cn.vo.GoodItem" id="goodsResultMap"&
&id property="gid" column="gid" javaType="int" jdbcType="INTEGER" /&
&result property="goodName" column="goodName" javaType="string" jdbcType="VARCHAR" /&
&result property="price" column="price" javaType="float" jdbcType="FLOAT" /&
&result property="good_sid" column="good_sid" javaType="int" jdbcType="INTEGER" /&
&/resultMap&
&select id="one2many" parameterType="int" resultMap="teacher"&
&!-- select
t.id,t.name,s.t_s_id,s.sid,s.sname
from teacher t
left join student s on t.id = s.t_s_id
left join goodItem g on g.good_sid=s.t_s_id
where t.id = #{id}
t.id,t.name,s.t_s_id,s.sid,s.sname,g.gid,g.goodname,g.price,g.good_sid
from teacher t
left join student s on
t.id = s.t_s_id
left join goodItem g on
g.good_sid = s.sid
where t.id = #{id}
以上是优化的结论：用一次请求解决n次请求查询
题目：在teacher 表中找到该 teacher下面的n个student并找出n个学生每个学生有多少个goods。
CREATE TABLE
name varchar(100) DEFAULT NULL,
PRIMARY KEY (id)
CREATE TABLE
sid number
sname varchar(100) DEFAULT NULL,
t_s_id number
PRIMARY KEY (sid)
insert into teacher(id,name) values(111,'zhangsan');
insert into teacher(id,name) values(222,'lisi');
insert into student(sid,sname,t_s_id) values(1,'xs1',111);
insert into student(sid,sname,t_s_id) values(2,'xs2',111);
insert into student(sid,sname,t_s_id) values(3,'xs3',222);
insert into student(sid,sname,t_s_id) values(4,'xs4',111);
select t.id,t.name,s.t_s_id,s.sid,s.sname
from teacher t
left join student s
on t.id = s.t_s_id where t.id = 111
create table goodItem(
gid number not null,
goodName varchar(10),
price float,
good_sid number
insert into goodItem(gid,Goodname,Price,Good_Sid)
values(1,'iphone6','6000',2);
insert into goodItem(gid,Goodname,Price,Good_Sid)
values(2,'iphone5','5000',2);
insert into goodItem(gid,Goodname,Price,Good_Sid)
values(3,'iphone4','4000',2);
insert into goodItem(gid,Goodname,Price,Good_Sid)
values(4,'iphone3','3000',1);
package com.cn.
public class Student {
public int getSid() {
public void setSid(int sid) {
this.sid =
public String getSname() {
public void setSname(String sname) {
this.sname =
package com.cn.
import java.util.L
public class Teacher {
private List&Student&
private List&GoodItem&
public List&GoodItem& getGoods() {
public void setGoods(List&GoodItem& goods) {
this.goods =
public int getId() {
public void setId(int id) {
public String getName() {
public void setName(String name) {
this.name =
public List&Student& getStudents() {
public void setStudents(List&Student& students) {
this.students =
package com.cn.
public class Item {
private String goodN
private Integer good_
public Integer getGid() {
public void setGid(Integer gid) {
this.gid =
public String getGoodName() {
return goodN
public void setGoodName(String goodName) {
this.goodName = goodN
public float getPrice() {
public void setPrice(float price) {
this.price =
public Integer getGood_sid() {
return good_
public void setGood_sid(Integer good_sid) {
this.good_sid = good_
package com.cn.
import java.util.L
public class GoodItem extends Item{
/* private List&Student&
private List&Teacher&
public List&Student& getStudents() {
public void setStudents(List&Student& students) {
this.students =
public List&Teacher& getTeachers() {
public void setTeachers(List&Teacher& teachers) {
this.teachers =
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