SQL SERVER - How to deal with the database Null (z)database

How to deal with the database Null (z)

How to deal with the database Null
Author: Oriental spider (to)

For beginners, in dealing with the Null database data types is a bit troublesome thing, in this article we will talk about the article Null, you will know how that is a Null value, which may or may not function handling Null

First, we must know that in VBScript, is the only one Variant data types, those who are already familiar with the development of programs in other languages, may feel a bit unaccustomed. Variant use of the benefits of their considerable flexibility because Variant can store any data type, for example, integer, string, date, time, including arrays and objects. However, flexibility is a price to pay, because the designated Variant than might be designated by the special data types to use much more memory

In the Variant data types there are two very special sub-type (Subtype): Empty and Null, in fact that may not be appropriate sub-type, because they do not store some value, when a variable is the type of information Empty or Null, and their value is Empty or Null

Empty

In a variable is declared, but its been designated a value before the variables in the types of information is Empty, in other words, the equivalent Empty "has not initialize", we take a look at the following example

Dim varTest
Response.Write TypeName (varTest)

Results for its implementation should be Empty, Empty can be said to be a variable of the initial data types and the initial value of a variable Empty only on behalf of the state, try the following example

Dim varTest
Response.Write CLng (varTest)
Response.Write CStr (varTest)

The first line program will show 0 as Empty been said that when the time for the integer 0, the second line will be the implementation of what is not, because that was when the string is Empty Empty, or can be said that the length is zero string

When a variable was designated a value, it will cease to be a Empty, it will be other sub-types, according to the types of data vary, of course, you can still use this keyword Empty these variables change to Empty - type

VarTest = Empty

There are two ways you can judge whether a variable Empty

If varTest = Empty Then
Response.Write "The variable is empty."
End If

If IsEmpty (varTest) Then
Response.Write "The variable is empty."
End If

Null

Null information of this type and Empty very similar, but the difference is Empty behalf of a variable has not been initialized, that is, has not been given any value, and a variable for you Null only after its designation as Null. The most commonly encountered Null opportunities should be in dealing with the database, when a column no information is Null

Null designation and the judge very similar methods and Empty

VarTest = Null

However, you can only use IsNull () function to determine Null, it is because Null is not represented by legal information, you can try the following examples

Dim varTest
VarTest = Null
If varTest = Null Then
Response.Write "The variable has a Null value."
End If

Implementation of the results will not show The variable has a Null value. A variable to determine whether you should use Null IsNull () function

Dim varTest
VarTest = Null
If IsNull (varTest) Then
Response.Write "The variable has a Null value."
End If

When you deal with the database in the Null removed the information, you have to be pretty attention because Null is not represented by legal information, when some function in dealing with math, Null may create some trouble, For example,

Dim varTest
VarTest = Null
VarTest = CLng (varTest)

You will see the results "Invalid Use of Null" error message, then look at the following example

Dim varTest
Dim lngTest
VarTest = Null
LngTest = 2 + varTest
Response.Write TypeName (lngTest)

You will find that, with two or Null Null Therefore, when you get the information from the database, you should first use IsNull () to determine whether the column Null, anything properly dealt with, for example,

LngQty = oRs ( "Quantuty")
If IsNull (lngQty) Then
LngQty = 0
End If

Hope this article will help you!

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