difference between null set and empty set

Method of NULL value processing for ORDER by orderingwhen the business data is sorted, it is found that some fields have a null value, then the order of the data is inconsistent with our usage. In Oracle, it is assumed that NULL is the maximum value

Meaning explanation:Q: What is NULL?A: When we do not know what the specific data, it is unknown, you can use NULL, we call it empty, Oracle, contains null values of the table column length is zero.Oracle allows fields of any one data type to be

The empty keyword is used to indicate the value of an uninitialized variable, unlike null Null keyword is used to indicate that the variable contains data that is not valid, unlike empty Instance: Dim p Now IsEmpty (p) is true IsNull (p) is null For

This article mainly introduces about a picture to clarify the difference between isset and empty function, has a certain reference value, now share to everyone, the need for friends can refer to A brief talk about the difference between isset and

Let's look at an effect chart first. When you define only one str instead of allocating memory for it, use string str=null, but you must assign a value to it before you use it, such as str= "XXXX", which is initialized for it.and string str=

Original: PHP isset () and empty () the use of a different explanationPHP's Isset () function is commonly used to detect whether a variable is setFormat: bool Isset (mixed var [, mixed Var [, ...])Function: Detect whether the variable is setreturn

First, let's take a look at the following:CodeWhat do you think are the results? StringSTR =String. Empty;StringStr1 ="";StringStr2 =Null;BoolT =String. Isnullorempty (STR );BoolT1 =String. Isnullorempty (str1 );BoolT2 =String. Isnullorempty (str2

By learning the language of PHP, you should know that it is a function-based HTML scripting language. The large library of functions supports the implementation of PHP language functions. Let's introduce the relevant usage of PHP function isset ()

PHP's Isset () function is commonly used to detect whether a variable is setFormat: bool Isset (mixed var [, mixed Var [, ...])Function: Detect whether the variable is setreturn value:Returns FALSE if the variable does not existReturns FALSE if the

Difference between PHP isset () and empty (), issetemptyThe isset () function of PHP is generally used to check whether the variable is set.Format: bool isset (mixed var [, mixed var [,...])Function: checks whether variables are set.Return Value:If