Java实现数据库表中的七种连接【Mysql】
- 前言
- 版权
- 推荐
- Java实现数据库表中的七种连接
- 左外连接
- 右外连接
- 其他连接
- 附录
- 七种连接
- SQL测试
- Java测试
- 转换方法
- 类 Cla1
- 类 Cla2
- 类Cla3
- 最后
前言
2023-8-4 16:51:42
以下内容源自《【Mysql】》
仅供学习交流使用
版权
禁止其他平台发布时删除以下此话
本文首次发布于CSDN平台
作者是CSDN@日星月云
博客主页是https://blog.csdn.net/qq_51625007
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推荐
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Java实现数据库表中的七种连接
左外连接
/**
* 左外连接
* 计算
* SELECT cla1.`id`,cla1.`type`,cla2.`name`
* FROM cla1
* LEFT JOIN cla2
* ON cla1.`id`=cla2.`id`
* (Where cla2.id IS NULL);
*
* @param list1
* @param list2
* @param isNull 有没有括号中的IS NULL这条语句
* @param out 输出吗？
* @return
*/
public static List<Cla3> leftJoin(List<Cla3> list1, List<Cla3> list2,boolean isNull,boolean out) {
List<Cla3> leftJoin=new ArrayList<>();
//左表遍历
list1.forEach(c1->{
//在右表中有没有找到
AtomicBoolean flag= new AtomicBoolean(false);
list2.forEach(c2->{
//找到了
if(c1.id.equals(c2.id)){
//如果cla2.id is null,就不需要添加
if (!isNull) {
leftJoin.add(new Cla3(c1.id, c1.type, c2.name));
}
flag.set(true);
}
});
//没有找到添加 右表属性 NULL
if(!flag.get()){
leftJoin.add(new Cla3(c1.id,c1.type,"null"));
}
});
return leftJoin;
}
右外连接
/**
* 右外连接
* 计算
* SELECT cla2.`id`,cla1.`type`,cla2.`name`
* FROM cla1
* RIGHT JOIN cla2
* ON cla1.`id`=cla2.`id`
* (WHERE cla1.`id` IS NULL);
*
* @param list1
* @param list2
* @param isNull 有没有括号中的IS NULL这条语句
* @return
*/
public static List<Cla3> rightJoin(List<Cla3> list1, List<Cla3> list2,boolean isNull,boolean out) {
List<Cla3> rightJoin=new ArrayList<>();
//右表遍历
list2.forEach(c2->{
//在左表中有没有找到
AtomicBoolean flag= new AtomicBoolean(false);
list1.forEach(c1->{
//找到了
if(c1.id.equals(c2.id)){
//如果cla1.id is null,就不需要添加
if (!isNull){
rightJoin.add(new Cla3(c2.id, c1.type,c2.name));
}
flag.set(true);
}
});
//没有找到添加 左表属性 NULL
if(!flag.get()){
rightJoin.add(new Cla3(c2.id,"null",c2.name));
}
});
return rightJoin;
}
其他连接
外连接
* 左外+右外
* 右外+左外
内连接
* 左外-左外ISNULL
* 右外-右外ISNULL
外连接-内连接
附录
七种连接
MySQL笔记：第06章_多表查询
SQL测试
CREATE DATABASE cla;
USE cla;
CREATE TABLE cla1(
`id` VARCHAR(10),
`type` VARCHAR(10)
);
CREATE TABLE cla2(
`id` VARCHAR(10),
`name` VARCHAR(10)
);
INSERT INTO cla1 VALUES('22','cde');
INSERT INTO cla1 VALUES('11','abc');
INSERT INTO cla1 VALUES('44','cdef');
INSERT INTO cla1 VALUES('55','cdefg');
INSERT INTO cla2
VALUES
('11','name1'),
('22','name2'),
('33','name3'),
('44','name4'),
('aa','nameaa');
#leftJoin
SELECT cla1.`id`,cla1.`type`,cla2.`name`
FROM cla1
LEFT JOIN cla2
ON cla1.`id`=cla2.`id`
/*
id type name
22 cde name2
11 abc name1
44 cdef name4
55 cdefg \N
*/
#leftJoin isnull
SELECT cla1.`id`,cla1.`type`,cla2.`name`
FROM cla1
LEFT JOIN cla2
ON cla1.`id`=cla2.`id`
WHERE cla2.`id` IS NULL;
/*
id type name
55 cdefg \N
*/
#rightJoin
SELECT cla2.`id`,cla1.`type`,cla2.`name`
FROM cla1
RIGHT JOIN cla2
ON cla1.`id`=cla2.`id`
/*
id type name
11 abc name1
22 cde name2
33 \N name3
44 cdef name4
aa \N nameaa
*/
#rightJoin ISNULL
SELECT cla2.`id`,cla1.`type`,cla2.`name`
FROM cla1
RIGHT JOIN cla2
ON cla1.`id`=cla2.`id`
WHERE cla1.`id` IS NULL;
/*
id type name
33 \N name3
aa \N nameaa
*/
#innerJoin leftBefore
SELECT cla1.`id`,cla1.`type`,cla2.`name`
FROM cla1
INNER JOIN cla2
ON cla1.`id`=cla2.`id`
/*
id type name
11 abc name1
22 cde name2
44 cdef name4
*/
#innerJoin rightBefore
SELECT cla2.`id`,cla1.`type`,cla2.`name`
FROM cla2
INNER JOIN cla1
ON cla2.`id`=cla1.`id`
/*
id type name
11 abc name1
22 cde name2
44 cdef name4
*/
#outJoin leftBefore
#左1+右2
SELECT cla1.`id`,cla1.`type`,cla2.`name`
FROM cla1
LEFT JOIN cla2
ON cla1.`id`=cla2.`id`
UNION ALL
SELECT cla2.`id`,cla1.`type`,cla2.`name`
FROM cla1
RIGHT JOIN cla2
ON cla1.`id`=cla2.`id`
WHERE cla1.`id` IS NULL;
/*
id type name
22 cde name2
11 abc name1
44 cdef name4
55 cdefg \N
33 \N name3
aa \N nameaa
*/
#outJoin rightBefore
#右1+左2
SELECT cla2.`id`,cla1.`type`,cla2.`name`
FROM cla1
RIGHT JOIN cla2
ON cla1.`id`=cla2.`id`
UNION ALL
SELECT cla1.`id`,cla1.`type`,cla2.`name`
FROM cla1
LEFT JOIN cla2
ON cla1.`id`=cla2.`id`
WHERE cla2.`id` IS NULL;
/*
id type name
11 abc name1
22 cde name2
33 \N name3
44 cdef name4
aa \N nameaa
55 cdefg \N
*/
Java测试
转换方法
package test.algo;
import test.algo.main2.Cla1;
import test.algo.main2.Cla2;
import test.algo.main2.Cla3;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicBoolean;
public class testJoin {
static List<Cla1> claList1 = new ArrayList<>();
static List<Cla2> claList2 = new ArrayList<>();
static List<Cla3> list1 = new ArrayList<>();
static List<Cla3> list2 = new ArrayList<>();
public static void main(String[] args) {
test();
init(claList1,claList2);
leftJoin(list1, list2,false,true);
/*
{id: 22, type: cde, name: name2}
{id: 11, type: abc, name: name1}
{id: 44, type: cdef, name: name4}
{id: 55, type: cdefg, name: null}
*/
leftJoin(list1, list2,true,true);;
/*
{id: 55, type: cdefg, name: null}
*/
rightJoin(list1, list2,false,true);
/*
{id: 11, type: abc, name: name1}
{id: 22, type: cde, name: name2}
{id: 33, type: null, name: name3}
{id: 44, type: cdef, name: name4}
{id: aa, type: null, name: nameaa}
*/
rightJoin(list1, list2,true,true);
/*
{id: 33, type: null, name: name3}
{id: aa, type: null, name: nameaa}
*/
outJoin(list1, list2,true,true);
/*
{id: 22, type: cde, name: name2}
{id: 11, type: abc, name: name1}
{id: 44, type: cdef, name: name4}
{id: 55, type: cdefg, name: null}
{id: 33, type: null, name: name3}
{id: aa, type: null, name: nameaa}
*/
outJoin(list1, list2,false,true);
/*
{id: 11, type: abc, name: name1}
{id: 22, type: cde, name: name2}
{id: 33, type: null, name: name3}
{id: 44, type: cdef, name: name4}
{id: aa, type: null, name: nameaa}
{id: 55, type: cdefg, name: null}
*/
innerJoin(list1,list2,true,true);
/*
{id: 22, type: cde, name: name2}
{id: 11, type: abc, name: name1}
{id: 44, type: cdef, name: name4}
*/
innerJoin(list1,list2,false,true);
/*
{id: 11, type: abc, name: name1}
{id: 22, type: cde, name: name2}
{id: 44, type: cdef, name: name4}
*/
outJoin_InnerJoin(list1,list2,true,true);
/*
{id: 55, type: cdefg, name: null}
{id: 33, type: null, name: name3}
{id: aa, type: null, name: nameaa}
*/
outJoin_InnerJoin(list1,list2,false,true);
/*
{id: 33, type: null, name: name3}
{id: aa, type: null, name: nameaa}
{id: 55, type: cdefg, name: null}
*/
}
/**
* 初始两个表中的数据
*/
public static void test(){
claList1.add(new Cla1("22", "cde"));
claList1.add(new Cla1("11", "abc"));
claList1.add(new Cla1("44", "cdef"));
claList1.add(new Cla1("55", "cdefg"));
claList2.add(new Cla2("11", "name1"));
claList2.add(new Cla2("22", "name2"));
claList2.add(new Cla2("33", "name3"));
claList2.add(new Cla2("44", "name4"));
claList2.add(new Cla2("aa", "nameaa"));
}
/**
* 初始结果表中的数据
*/
public static void init(List<Cla1> claList1, List<Cla2> claList2){
claList1.forEach(cla1 -> list1.add(new Cla3(cla1.getId(), cla1.getType(), "null")));
claList2.forEach(cla2 -> list2.add(new Cla3(cla2.getId(), "null", cla2.getName())));
}
/**
*外连接-内连接
* @param list1
* @param list2
* @param leftBefore 左边在前
* @param out 是否输出
* @return
*/
public static List<Cla3> outJoin_InnerJoin(List<Cla3> list1, List<Cla3> list2,boolean leftBefore,boolean out){
List<Cla3> outJoin_InnerJoin=new ArrayList<>();
outJoin_InnerJoin.addAll(outJoin(list1, list2, leftBefore, false));
outJoin_InnerJoin.removeAll(innerJoin(list1, list2, leftBefore, false));
if(out){
System.out.println("--------------------outJoin_InnerJoin"+((leftBefore)?"leftBefore":"rightBefore")+"-------------------------------");
outJoin_InnerJoin.forEach(System.out::println);
System.out.println("--------------------outJoin_InnerJoin"+((leftBefore)?"leftBefore":"rightBefore")+"-------------------------------");
}
return outJoin_InnerJoin;
}
/**
* 内连接
* 左外-左外ISNULL
* 右外-右外ISNULL
* @param list1
* @param list2
* @param leftBefore 左边在前
* @param out 是否输出
* @return
*/
public static List<Cla3> innerJoin(List<Cla3> list1, List<Cla3> list2,boolean leftBefore,boolean out){
List<Cla3> innerJoin=new ArrayList<>();
if(leftBefore){
innerJoin.addAll(leftJoin(list1, list2, false, false));
innerJoin.removeAll(leftJoin(list1, list2, true, false));
}else {
innerJoin.addAll(rightJoin(list1, list2, false, false));
innerJoin.removeAll(rightJoin(list1, list2, true, false));
}
if(out){
System.out.println("--------------------innerJoin"+((leftBefore)?"leftBefore":"rightBefore")+"-------------------------------");
innerJoin.forEach(System.out::println);
System.out.println("--------------------innerJoin"+((leftBefore)?"leftBefore":"rightBefore")+"-------------------------------");
}
return innerJoin;
}
/**
* 左外连接
* 计算
* SELECT cla1.`id`,cla1.`type`,cla2.`name`
* FROM cla1
* LEFT JOIN cla2
* ON cla1.`id`=cla2.`id`
* (Where cla2.id IS NULL);
*
* @param list1
* @param list2
* @param isNull 有没有括号中的IS NULL这条语句
* @param out 输出吗？
* @return
*/
public static List<Cla3> leftJoin(List<Cla3> list1, List<Cla3> list2,boolean isNull,boolean out) {
List<Cla3> leftJoin=new ArrayList<>();
list1.forEach(c1->{
AtomicBoolean flag= new AtomicBoolean(false);
list2.forEach(c2->{
if(c1.id.equals(c2.id)){
if (!isNull) {
leftJoin.add(new Cla3(c1.id, c1.type, c2.name));
}
flag.set(true);
}
});
if(!flag.get()){
leftJoin.add(new Cla3(c1.id,c1.type,"null"));
}
});
if(out){
System.out.println("--------------------leftJoin---"+((isNull)?"isNull":"----")+"-------------------------------");
leftJoin.forEach(System.out::println);
System.out.println("--------------------leftJoin---"+((isNull)?"isNull":"----")+"-------------------------------");
System.out.println();
}
return leftJoin;
}
/**
* 右外连接
* 计算
* SELECT cla2.`id`,cla1.`type`,cla2.`name`
* FROM cla1
* RIGHT JOIN cla2
* ON cla1.`id`=cla2.`id`
* (WHERE cla1.`id` IS NULL);
*
* @param list1
* @param list2
* @param isNull 有没有括号中的IS NULL这条语句
* @return
*/
public static List<Cla3> rightJoin(List<Cla3> list1, List<Cla3> list2,boolean isNull,boolean out) {
List<Cla3> rightJoin=new ArrayList<>();
list2.forEach(c2->{
AtomicBoolean flag= new AtomicBoolean(false);
list1.forEach(c1->{
if(c1.id.equals(c2.id)){
if (!isNull){
rightJoin.add(new Cla3(c2.id, c1.type,c2.name));
}
flag.set(true);
}
});
if(!flag.get()){
rightJoin.add(new Cla3(c2.id,"null",c2.name));
}
});
if (out){
System.out.println("--------------------rightJoin---"+((isNull)?"isNull":"----")+"-------------------------------");
rightJoin.forEach(System.out::println);
System.out.println("--------------------rightJoin---"+((isNull)?"isNull":"----")+"-------------------------------");
System.out.println();
}
return rightJoin;
}
/**
* 外连接
* 左外+右外
* 右外+左外
* SELECT *
* FROM tableA A
* FULL OUTER JOIN TableB B
* ON A.key=B.key
*
* @param leftBefore 结果集左表在前还是右边在前
* @param out 输出吗
* @return
*/
public static List<Cla3> outJoin(List<Cla3> list1, List<Cla3> list2,boolean leftBefore,boolean out) {
List<Cla3> outJoin=new ArrayList<>();
List<Cla3> leftJoin = leftJoin(list1, list2,!leftBefore,false);
List<Cla3> rightJoin = rightJoin(list1, list2,leftBefore,false);
if (leftBefore){
outJoin.addAll(leftJoin);
outJoin.addAll(rightJoin);
}else {
outJoin.addAll(rightJoin);
outJoin.addAll(leftJoin);
}
if(out){
System.out.println("--------------------outJoin"+((leftBefore)?"leftBefore":"rightBefore")+"-------------------------------");
outJoin.forEach(System.out::println);
System.out.println("--------------------outJoin"+((leftBefore)?"leftBefore":"rightBefore")+"-------------------------------");
}
return outJoin;
}
}
类 Cla1
package test.algo.main2;
public class Cla1 {
public String id;
public String type;
public Cla1(String id, String type) {
this.id = id;
this.type = type;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
@Override
public String toString() {
return "{id: " + id + ", type: " + type + "}";
}
}
类 Cla2
package test.algo.main2;
public class Cla2 {
public String id;
public String name;
public Cla2(String id, String name) {
this.id = id;
this.name = name;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "{id: " + id + ", name: " + name + "}";
}
}
类Cla3
需要重写equals()
id==id
package test.algo.main2;
import java.util.Objects;
public class Cla3 {
public String id;
public String name;
public String type;
public Cla3(String id, String type, String name) {
this.id = id;
this.type = type;
this.name = name;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Cla3 cla3 = (Cla3) o;
return Objects.equals(id, cla3.id);
}
@Override
public int hashCode() {
return Objects.hash(id);
}
@Override
public String toString() {
return "{id: " + id + ", type: " + type + ", name: " + name + "}";
}
}
最后
2023-8-4 17:04:28
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