Mysql 如何实现多张无关联表查询数据并分页

Mysql 多张无关联表查询数据并分页

功能需求

在三张没有主外键关联的表中取出自己想要的数据，并且分页。

数据库表结构

水果表：

坚果表：

饮料表：

数据库随便建的，重在方法。

主要使用UNION ALL 操作符

UNION ALL 操作符用于合并两个或多个 SELECT 语句的结果集。

请注意，UNION ALL内部的 SELECT 语句必须拥有相同数量的列。列也必须拥有相似的数据类型。同时，每条 SELECT 语句中的列的顺序必须相同 ; 另外，UNION ALL结果集中的列名总是等于 UNION ALL中第一个 SELECT 语句中的列名。

// 详细sql语句
select * FROM
(
	(select fid,fname,price,type from fruits)
	UNION ALL
	(select nid,name,price,6 as type from nut)
	UNION ALL
	(select did,dname,price,7 as type from drinks)
	
) as fnd limit 0,10     -----fnd为表的别名

最终结果

mysql多表联合查询时出现的分页问题的解决

mysql一对多分页问题

部门表：tbl_dept

员工表：tbl_emp

数据库sql文件

 
CREATE DATABASE /*!32312 IF NOT EXISTS*/`ssm-crud` /*!40100 DEFAULT CHARACTER SET utf8 */;
 
USE `ssm-crud`;
 
/*Table structure for table `tbl_dept` */
 
DROP TABLE IF EXISTS `tbl_dept`;
 
CREATE TABLE `tbl_dept` (
  `dept_id` int(11) NOT NULL AUTO_INCREMENT,
  `dept_name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`dept_id`)
) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;
 
/*Data for the table `tbl_dept` */
 
insert  into `tbl_dept`(`dept_id`,`dept_name`) values 
(1,'技术部'),
(2,'业务部'),
(6,'销售部'),
(7,'人事部');
 
/*Table structure for table `tbl_emp` */
 
DROP TABLE IF EXISTS `tbl_emp`;
 
CREATE TABLE `tbl_emp` (
  `emp_id` int(11) NOT NULL AUTO_INCREMENT,
  `emp_name` varchar(255) DEFAULT NULL,
  `emp_gender` char(1) DEFAULT NULL,
  `emp_email` varchar(255) DEFAULT NULL,
  `d_id` int(11) DEFAULT NULL,
  PRIMARY KEY (`emp_id`),
  KEY `FK_tbl_emp` (`d_id`),
  CONSTRAINT `FK_tbl_emp` FOREIGN KEY (`d_id`) REFERENCES `tbl_dept` (`dept_id`)
) ENGINE=InnoDB AUTO_INCREMENT=14 DEFAULT CHARSET=utf8;
 
/*Data for the table `tbl_emp` */
 
insert  into `tbl_emp`(`emp_id`,`emp_name`,`emp_gender`,`emp_email`,`d_id`) values 
(1,'xiaoshen','2',NULL,6),
(4,'晓明','1',NULL,1),
(5,'xiaohong','2',NULL,2),
(6,'xiaohei','2',NULL,6),
(7,'xiaozhang','1',NULL,1),
(8,'xiaogao','1',NULL,1),
(9,'xiaohua','1',NULL,1),
(10,'xiaoyan','2',NULL,1),
(11,'xiaohai','2',NULL,2),
(12,'xiaoqiang','1',NULL,6),
(13,'xiaoqi','2',NULL,7);

分页错误写法(主查询员工表)

SELECT * FROM tbl_emp e
LEFT JOIN 
tbl_dept d
 
ON d.dept_id  = e.d_id
 
LIMIT 1,10

使用子查询方式解决问题

SELECT
        *
    FROM
     (
       SELECT
       *
        FROM
        tbl_emp e
        LEFT JOIN 
    tbl_dept d
        ON d.dept_id  = e.d_id
        
        GROUP BY e.d_id
        LIMIT 1,10
 
     ) e
 
      LEFT JOIN tbl_dept d
        ON d.dept_id  = e.d_id

下面代码与之无关 仅为备份

SELECT
        ft.id,
        ft.partner_id AS partnerId,
        ft.code ,
        ft.end_update_date AS  endUpdateDate,
        ft.name ,
        ft.type ,
        ft.area ,
        ft.is_default AS  isDefault,
        fp.id fpId,
        fp.shop_id AS fpShopId  ,
        fp.provice_id AS fpProviceId ,
        fp.provice_name AS fpProviceName ,
        fp.start_num  AS fpStartNum ,
        fp.start_fee  AS fpStartFee ,
        fp.increase_num AS fpIncreaseNum ,
        fp.increase_fee AS fpIncreaseFee ,
        fp.code AS fpCode ,
        fp.provice_text AS  fpProviceText ,
        fp.template_id AS fpTemplateId
    FROM
     (
       SELECT
        f.id,
        f.partner_id ,
        f.code ,
        f.end_update_date  ,
        f.name ,
        f.type ,
        f.area ,
        f.is_default ,
        f.is_del,
        f.create_date
        FROM
        bus_freight_template f
        LEFT JOIN bus_freight_provice p
        ON f.id = p.template_id
        WHERE f.code = p.code
        AND f.code = #[code]
        GROUP BY f.id
        LIMIT #{startPage},#{pageSize}
 
     ) ft
 
      LEFT JOIN bus_freight_provice fp
        ON ft.id = fp.template_id
    WHERE ft.code = fp.code
      AND fp.template_id IS NOT NULL
      AND ft.code =  #[code]
      AND fp.is_del = '0'
      AND ft.is_del = '0'
 
      order by ft.create_date desc

以上为个人经验，希望能给大家一个参考，也希望大家多多支持NICE源码。