database - PostgreSQL 11.5 级联更新多列一行

Question

我有一个名为 device_statistics 的表，它存储一个应用程序的设备信息，表创建脚本是：

CREATE TABLE public.device_statistics
(
    id character varying(255) COLLATE pg_catalog."default" NOT NULL,
    abnormalcount integer,
    appid character varying(32) COLLATE pg_catalog."default" NOT NULL,
    inactivecount integer,
    offlinecount integer,
    onlinecount integer,
    statisticstime date,
    totalcount integer,
    CONSTRAINT ods_device_statistics_pkey PRIMARY KEY (id)
)

当设备离线时，我必须更新离线计数值，因为totalcount=abnormalcount + inactivecount + offlinecount + onlinecount这样我可以在异常计数、非活动计数、离线计数或在线计数更新时自动更新总计数值。

例如：

在设备离线之前，行如下（仅显示我们需要）：

appid  offlinecount totalcount

test        10            32

当设备离线并且我更新离线计数值时，我想要如下行：

appid  offlinecount totalcount
test       9           31

totalcout 的值是自动更新的，怎么办？

Answer 1

在 PostgreSQL 12 之前，您可以改为创建视图：

CREATE TABLE public.device_statistics
(
    id character varying(255) COLLATE pg_catalog."default" NOT NULL,
    abnormalcount integer,
    appid character varying(32) COLLATE pg_catalog."default" NOT NULL,
    inactivecount integer,
    offlinecount integer,
    onlinecount integer,
    statisticstime date,
    CONSTRAINT ods_device_statistics_pkey PRIMARY KEY (id)
)

CREATE OR REPLACE VIEW public.device_statistics_with_total AS
SELECT id,
       abnormalcount,
       appid,
       inactivecount,
       offlinecount,
       onlinecount,
       statisticstime,
       abnormalcount + inactivecount + offlinecount + onlinecount AS totalcount
FROM device_statistics;

如果您有能力升级到 PostgreSQL v. 12，您可以使用新的生成列功能：

CREATE TABLE public.device_statistics
(
    id character varying(255) COLLATE pg_catalog."default" NOT NULL,
    abnormalcount integer,
    appid character varying(32) COLLATE pg_catalog."default" NOT NULL,
    inactivecount integer,
    offlinecount integer,
    onlinecount integer,
    statisticstime date,
    totalcount integer GENERATED ALWAYS AS (abnormalcount + inactivecount + offlinecount + onlinecount) STORED,
    CONSTRAINT ods_device_statistics_pkey PRIMARY KEY (id)
)

披露：我为EnterpriseDB (EDB)工作