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的预订数据库编写预订过程，而我真正想做的是这样的事情：
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。我想知道是否有某种方法可以做到这一点，或者在这一步中是否仅需要某些用户交互？
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
该特定命令可以这样完成：
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 * from leadcustomer where firstname = 'John' and surname = 'Smith'
);
它将插入select语句的结果和 select 仅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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