UNION和UNION ALL的用法与区别

前言

在MySQL中，可以使用UNION和UNION ALL查询多多条结果，并且它们的结果组合成单个结果集。合并时，两个表对应的列数和数据类型必须相同

使用

1、建立light_devcice表

sql 复制代码

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for light_device
-- ----------------------------
DROP TABLE IF EXISTS `light_device`;
CREATE TABLE `light_device`  (
  `id` bigint NOT NULL AUTO_INCREMENT,
  `tenant_id` bigint NULL DEFAULT NULL COMMENT '租户ID',
  `org_id` bigint NOT NULL COMMENT '机构ID',
  `host_id` bigint NOT NULL COMMENT '网关设备ID',
  `device_id` bigint NOT NULL COMMENT '设备ID',
  `parent_device_id` bigint NULL DEFAULT NULL COMMENT '父设备ID',
  `device_name` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '设备名称',
  `device_remark` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '设备备注',
  `device_sn` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '设备唯一标识',
  `device_type` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '设备类型',
  `device_category` int NULL DEFAULT NULL COMMENT '设备分类',
  `region_id` bigint NULL DEFAULT NULL COMMENT '区域ID',
  `display_flag` tinyint NULL DEFAULT 1 COMMENT '是否显示(网关):1>显示;0>不显示',
  `terminal_flag` tinyint NULL DEFAULT 0 COMMENT '带终端设备能力:1>是;0>否',
  `control_flag` tinyint NULL DEFAULT 0 COMMENT '控制能力:1>是;0>否',
  `delete_flag` tinyint NULL DEFAULT 0 COMMENT '是否删除:1：是；0否',
  `create_by` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '创建人',
  `update_by` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '更新人',
  `create_time` datetime NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
  `update_time` datetime NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  `saas_device_id` bigint NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE,
  UNIQUE INDEX `device_id_UNIQUE`(`device_id` ASC) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1899370485329244162 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_bin ROW_FORMAT = DYNAMIC;

SET FOREIGN_KEY_CHECKS = 1;

2、建立light_device_property表

sql 复制代码

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for light_device_property
-- ----------------------------
DROP TABLE IF EXISTS `light_device_property`;
CREATE TABLE `light_device_property`  (
  `id` bigint NOT NULL AUTO_INCREMENT,
  `tenant_id` bigint NULL DEFAULT NULL COMMENT '租户ID',
  `org_id` bigint NOT NULL COMMENT '机构ID',
  `host_id` bigint NULL DEFAULT NULL COMMENT '网关ID',
  `device_sn` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '设备唯一标识',
  `device_id` bigint NOT NULL COMMENT '设备ID',
  `device_key` int NOT NULL COMMENT '设备属性ID',
  `property_name` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '属性名称',
  `property_remark` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '设备备注',
  `display_flag` tinyint NULL DEFAULT 1 COMMENT '是否显示(网关):1>显示;0>不显示',
  `delete_flag` tinyint NULL DEFAULT 0 COMMENT '是否删除:1：是；0否',
  `region_id` bigint NOT NULL COMMENT '区域ID',
  `create_by` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '创建人',
  `update_by` varchar(45) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '更新人',
  `create_time` datetime NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
  `update_time` datetime NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '更新时间',
  `load_dev_type` int NULL DEFAULT NULL COMMENT '终端设备类型：开关量输入设备、继电器输出设备类型、无线终端设备类型。',
  `saas_device_id` bigint NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1897904309122183171 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_bin ROW_FORMAT = DYNAMIC;

SET FOREIGN_KEY_CHECKS = 1;

使用union查询

css 复制代码

  select p.id              as propertyId,
        p.device_id       as deviceId,
        p.property_name   as deviceName,
        p.device_key      as deviceKey,
        p.property_remark as deviceRemark,
        p.host_id as hostId,
        p.load_dev_type as deviceType,
        p.display_flag as display,
        p.saas_device_id as saasDeviceId
        from light_device_property p
        where p.org_id = 1853960415193595905
        
         union
        select p.id              as propertyId,
        p.device_id       as deviceId,
        p.device_name   as deviceName,
        null as deviceKey,
        p.device_remark as deviceRemark,
        p.host_id as hostId,
        p.device_type as deviceType,
        p.display_flag as display,
        p.saas_device_id as saasDeviceId
        from light_device p
        where p.org_id = 1853960415193595905

返回值为

如果使用该sql

csharp 复制代码

  select p.id              as propertyId
        from light_device_property p
        where p.org_id = 1853960415193595905
        
         union
        select p.id              as propertyId
        from light_device p
        where p.org_id = 1853960415193595905

会发现如果两个表有重复id，不会出现重复记录

css 复制代码

 select p.id              as propertyId
        from light_device_property p
        where p.org_id = 1853960415193595905
        
         union all
        select p.id              as propertyId
        from light_device p
        where p.org_id = 1853960415193595905

会发现如果两个表有重复id，会出现重复记录

总结

UNION 从查询结果集中自动去除了重复的行，如果要返回所有匹配行，而不进行删除，可以使用 UNION ALL。