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12 Ιουν 2018 · What is the meaning of null? How is null implemented? When should you use null in your source code, and when should you not use it? Introduction. null is a fundamental concept in many programming languages. It is ubiquitous in all kinds of source code written in these languages. So it is essential to fully grasp the idea of null.
What is a NULL Value? A field with a NULL value is a field with no value. If a field in a table is optional, it is possible to insert a new record or update a record without adding a value to this field. Then, the field will be saved with a NULL value.
The NULL value means "no data." NULL can be written in any lettercase. A synonym is \N (case sensitive). NOT NULL would mean the opposite of NULL, or not no data. Since some columns can be NULL, you use WHERE col IS NOT NULL to find values that are not "empty."
2 Ιουν 2016 · For the rest of this article, I will use the convention that "NULL" (all uppercase letters) means "database null" and "null" (all lowercase letters) means "programming language null". One consequence of defining NULL differently from null is that one cannot use ordinary Boolean logic.
24 Απρ 2023 · A NULL value is not equivalent to a value of ZERO if the data type is a number and is not equivalent to spaces if the data type is a character. A NULL value can be inserted into columns of any data type. A NULL value will evaluate NULL in any expression.
5 Σεπ 2014 · A null value is used in databases to signify a missing or unknown value. A NULL can be tricky. NULL = NULL is false!
Let us talk about the concept of NULL values in a database for a little: NULL means something is unknown. It does NOT mean null (the digit 0). Null (or zero, the digit) is a known value: You can include 0 in calculations, whilst NULL stands for "value is unknown".
