Top "Exists" questions

Check if record exists from controller in Rails

In my app a User can create a Business. When they trigger the index action in my BusinessesController I want …

ruby-on-rails ruby-on-rails-3 activerecord exists

MongoDB: How to query for records where field is null or not set?

I have an Email document which has a sent_at date field: { 'sent_at': Date( 1336776254000 ) } If this Email has not …

mongodb null mongodb-query exists

SQL: Return "true" if list of records exists?

An alternative title might be: Check for existence of multiple rows? Using a combination of SQL and C# I want …

c# sql conditional boolean exists

how to prevent "directory already exists error" in a makefile when using mkdir

I need to generate a directory in my makefile and I would like to not get the "directory already exists …

makefile directory exists

How to fix "Only one expression can be specified in the select list when the subquery is not introduced with EXISTS" error?

I'm trying to run the following query on MS SQL 2012 Express: Select ( Select Id, Salt, Password, BannedEndDate from Users where …

sql sql-server tsql exists

PL/pgSQL checking if a row exists

I'm writing a function in PL/pgSQL, and I'm looking for the simplest way to check if a row exists. …

sql postgresql plpgsql postgresql-9.1 exists

Oracle sql return true if exists question

How do I check if a particular element exists in a table - how can I return true or false? …

sql oracle if-statement exists

Set Variable value in exists condition sql server

Declare @CategoryID as int BEGIN SELECT (CASE WHEN EXISTS( SELECT t0.Categoryid AS [EMPTY] FROM Categories AS [t0] WHERE [t0].…

sql sql-server sql-server-2008 exists

Checking whether an item does not exist in another table

My tables are set up something like this: table name: process fields: name, id_string table name: value_seach fields: …

sql oracle exists anti-join

How to check if a file exists and is readable in C++?

I've got a fstream my_file("test.txt"), but I don't know if test.txt exists. In case it exists, …

c++ linux file fstream exists