postgres 中的条件 INSERT INTO 语句 [英] Conditional INSERT INTO statement in postgres
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问题描述
我正在为模拟航空公司预订数据库编写预订程序，我真正想做的是这样的:
I'm writing a booking procedure for a mock airline booking database and what I really want to do is something like this:
IF EXISTS (SELECT * FROM LeadCustomer
WHERE FirstName = 'John' AND Surname = 'Smith')
THEN
INSERT INTO LeadCustomer (Firstname, Surname, BillingAddress, email)
VALUES ('John', 'Smith', '6 Brewery close,
Buxton, Norfolk', 'cmp.testing@example.com');
但是 Postgres 不支持 IF 语句而不加载 PL/pgSQL 扩展.我想知道是否有办法做到这一点，或者在这一步中是否需要进行一些用户交互?
But Postgres doesn't support IF statements without loading the PL/pgSQL extension. I was wondering if there was a way to do some equivalent of this or if there's just going to have to be some user interaction in this step?
推荐答案
具体的命令可以这样写:
That specific command can be done like this:
insert into LeadCustomer (Firstname, Surname, BillingAddress, email)
select
'John', 'Smith',
'6 Brewery close, Buxton, Norfolk', 'cmp.testing@example.com'
where not exists (
select 1 from leadcustomer where firstname = 'John' and surname = 'Smith'
);
它会插入select语句的结果，select只会在该客户不存在时返回一行.
It will insert the result of the select statement, and the select will only return a row if that customer does not exist.
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