sql - 如何修复重复键值违反 Postges 9+ 中的唯一约束错误

Question

有时奇怪的重复键错误

duplicate key value violates unique constraint "session_pkey"
Key (workplace)=(WIN-N9BSKUNKBC8 ) already exists.

出现在脚本中：

delete from session where workplace='WIN-N9BSKUNKBC8' ;
INSERT INTO session (workplace,ipaddress,logintime,loggeduser)
SELECT 'WIN-N9BSKUNKBC8' , inet_client_addr()::CHAR(14),current_timestamp::CHAR(28),CURRENT_USER WHERE NOT EXISTS (SELECT 1 FROM session WHERE workplace='WIN-N9BSKUNKBC8' )

Sript 每 10 分钟运行一次窗体 Windows 任务调度程序。错误只是偶尔发生。

如何解决这个问题？表定义为

CREATE TABLE public.session
(
    loggeduser character(10) ,
    workplace character(16) NOT NULL,
    ipaddress character(20) ,
    logintime character(28) ,
    activity timestamp with time zone,
    CONSTRAINT session_pkey PRIMARY KEY (workplace)
)

环境：

PostgreSQL 13.1, compiled by Visual C++ build 1914, 64-bit
Windows server 2019
psqlODBC driver 13.00.0000

Answer 1

您可以使用on conflict：

INSERT INTO session (workplace,ipaddress,logintime,loggeduser)
    SELECT 'WIN-N9BSKUNKBC8',     
          inet_client_addr()::CHAR(14),current_timestamp::CHAR(28),
CURRENT_USER 
    ON CONFLICT DO NOTHING;

鉴于您只有一行进入，我的猜测是问题出在并发问题上。