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How can I determine if a variable is ‘undefined’ or ‘null’?

Why does Oracle 9i treat an empty string as NULL?

I believe the answer is that Oracle is very, very old. Back in the olden days before there was a SQL standard, Oracle made the design decision that empty strings in VARCHAR/VARCHAR2 columns were NULL and that there was only one sense of NULL (there are relational theorists that would differentiate between data that has … Read more

Origin null is not allowed by Access-Control-Allow-Origin

Origin null is the local file system, so that suggests that you’re loading the HTML page that does the load call via a file:/// URL (e.g., just double-clicking it in a local file browser or similar). Most browsers apply the Same Origin Policy to local files by disallowing even loading files from the same directory … Read more

return, return None, and no return at all?

On the actual behavior, there is no difference. They all return None and that’s it. However, there is a time and place for all of these. The following instructions are basically how the different methods should be used (or at least how I was taught they should be used), but they are not absolute rules … Read more

Sort by column ASC, but NULL values first?

Postgres has the NULLS FIRST | LAST modifiers for ORDER BY expression: … ORDER BY last_updated NULLS FIRST The typical use case is with descending sort order (DESC), which produces the complete inversion of the default ascending order (ASC) with null values first – which is often not desirable. To sort NULL values last: … … Read more

What is null in Java?

Is null an instance of anything? No, there is no type which null is an instanceof. 15.20.2 Type Comparison Operator instanceof RelationalExpression: RelationalExpression instanceof ReferenceType At run time, the result of the instanceof operator is true if the value of the RelationalExpression is not null and the reference could be cast to the ReferenceType without … Read more

What is the difference between null and undefined in JavaScript?

Method Overloading for null argument

Java will always try to use the most specific applicable version of a method that’s available (see JLS §15.12.2). Object, char[] and Integer can all take null as a valid value. Therefore all 3 version are applicable, so Java will have to find the most specific one. Since Object is the super-type of char[], the … Read more

What is the difference between NULL, ‘\0’ and 0?

Note: This answer applies to the C language, not C++. Null Pointers The integer constant literal 0 has different meanings depending upon the context in which it’s used. In all cases, it is still an integer constant with the value 0, it is just described in different ways. If a pointer is being compared to … Read more

NULL values inside NOT IN clause

Query A is the same as: select ‘true’ where 3 = 1 or 3 = 2 or 3 = 3 or 3 = null Since 3 = 3 is true, you get a result. Query B is the same as: select ‘true’ where 3 <> 1 and 3 <> 2 and 3 <> null When … Read more