在 postgresql 查询中检查布尔值真/假结果
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/17812253/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
checking for boolean true / false result in postgresql query
提问by mark li
I am running the following sql query in my web app:
我在我的 Web 应用程序中运行以下 sql 查询：
SELECT EXISTS (
SELECT id
FROM user
WHERE membership=1244)
i was expecting true(boolean data) as the result but I'm getting 't' or 'f' for false. How do I get it to return to my lua code a standard boolean?
我期待结果为真（布尔数据），但我得到 't' 或 'f' 为假。如何让它返回到我的 lua 代码标准布尔值？
I found the following post:
我找到了以下帖子：
Reading boolean correctly from Postgres by PHP
And so I tried to change my code to something like this:
所以我试着把我的代码改成这样：
SELECT EXISTS ::int (
SELECT id
FROM user
WHERE membership=1244)
or
或者
SELECT ::INT (SELECT EXISTS (
SELECT id
FROM user
WHERE membership=1244))
But I'm getting a syntax error.
Can you tell the best way to handle this? Should I be casting the resulting 't' to a boolean somehow? or is there a way to tell postgresql to return true / false instead of 't'/'f'?
但我收到语法错误。
你能说出处理这个问题的最佳方法吗？我应该以某种方式将结果“t”转换为布尔值吗？或者有没有办法告诉postgresql返回真/假而不是't'/'f'？
Thanks.
谢谢。
回答by Barbara Laird
You are so close
你是如此接近
SELECT EXISTS (SELECT id FROM user WHERE membership=1244)::int
回答by slavoo
Try it with CASE
试试看 CASE
select
(case when exists (SELECT id FROM user WHERE membership = 1244)
then 1
else 0
end) as column;
回答by Clodoaldo Neto
Your first query do indeed return a boolean. A tis shown as the returned value of the query
您的第一个查询确实返回一个布尔值。At显示为查询的返回值
select exists (select 1);
exists
--------
t
But if you check its type it is a boolean:
但是如果你检查它的类型，它是一个布尔值：
select pg_typeof(exists (select 1));
pg_typeof
-----------
boolean
You will have to check with the lua's postgresql driver manual how to properly handle it.
您必须查看 lua 的 postgresql 驱动程序手册如何正确处理它。
回答by Milen A. Radev
Your initial query is fine by itself:
您的初始查询本身很好：
SELECT id FROM user WHERE membership=1244
You just need to check if it returns a row or not.
您只需要检查它是否返回一行。
