Question

这是我们可以检查MSSQL中表是否存在的方式：

IF OBJECT_ID(N'public."TABLE_NAME"', N'U') IS NOT NULL
select 1 as 'column'
else 
select 0 as 'column';

将结果存储在变量“ column”中

我如何在PostgreSQL中做同样的事情？我想分别返回1或0。

Answer 1

将SELECT与EXISTS运算符一起使用，例如检查information_schema.tables：

select exists (select *
               from information_schema.tables
               where table_name = 'table_name' 
                 and table_schema = 'public') as table_exists;

如果您不能（或不会）处理正确的布尔值，只需将结果转换为数字即可（但我不知道为什么这样做会更好）：

select exists (select *
               from information_schema.tables
               where table_name = 'table_name' 
                 and table_schema = 'public')::int as "column";

请注意，column是保留关键字，因此您需要使用双引号将其引起来。

Answer 2

检查表是否存在使用视图pg_tables的列

$ClientID       = "a6ec906d-xxxxx00dd3" #ApplicationID
$ClientSecret   = "XwaNxxxxx/44"  #key from Application
$tennantid      = "bb58xxxxxxd6c65"
$objectid       = "ca8xxxef66db07c0" #object id of the application

$TokenEndpoint = {https://login.windows.net/{0}/oauth2/token} -f $tennantid 
$ARMResource = "https://graph.windows.net/";

$Body = @{
        'resource'= $ARMResource
        'client_id' = $ClientID
        'grant_type' = 'client_credentials'
        'client_secret' = $ClientSecret
}

$params = @{
    ContentType = 'application/x-www-form-urlencoded'
    Headers = @{'accept'='application/json'}
    Body = $Body
    Method = 'Post'
    URI = $TokenEndpoint
}

$token = Invoke-RestMethod @params

$accesstoken = $token.access_token

$url = {https://graph.windows.net/{0}/applications/{1}?api-version=1.6} -f $tennantid,$objectid

$header = @{
    'Authorization' = 'Bearer ' + $accesstoken
    'Content-Type' = 'application/json'
}

$json = @{
    oauth2AllowIdTokenImplicitFlow = 'false' #or true
}

$body = $json | ConvertTo-Json

Invoke-RestMethod –Uri $url –Headers $header -Body $body –Method PATCH

对于我的SQL，使用INFORMATION_SCHEMA.COLUMNS

IF EXISTS ( SELECT attname 
    FROM pg_attribute 
    WHERE attrelid = (SELECT oid FROM pg_class WHERE relname = 'YOURTABLENAME') 
    AND attname = 'YOURCOLUMNNAME')
THEN
-- do something
END IF;

PostgreSQL如何检查表是否存在？

2 个答案: