if null then

Example code:/** * If the barcode field value is NULL then do not process * If the barcode field value is not null before the original value of the Mosaic del:@param dealer @return * /@Modifying @Transactional @Query

If the value of an object is null, does it give an error when calling an extension method?Person p = null;p. Extendmethod ();The above code will not be an error, the beginning of this situation is very puzzled, asked Daniel. Daniel explains the

In the database, a null value is used to indicate that the actual value is unknown or meaningless. In a table, if a column in a row has no value, it is called NULL ). A null value can be returned for any data type column as long as the non-NULL or

1 Introduction to null valuesNULL is a unique data type in the database. If a column in a record is NULL, the value of this column is unknown and uncertain. Since it is unknown, there are several possibilities. Therefore, NULL is not a definite

 First look at the following section of code output what:#include int main () { int *p=null; printf ("%s", p); }Output , single-step debugging you can see that the value of executing int *p=null,p is 0x00000000, as you can see, NULL is 0 in

For Java programmers, NULL is a headache. is often harassed by null-pointer anomalies (NPE). Even the inventor of Java admits it was a huge mistake. Why should Java keep null? Null has been around for some time, and I think the Java inventor knows

MySQL Trigger if then ElseIf else's useCREATE PROCEDURE DBName.Proc_getgrade(Stu_no varchar(20),Cour_no varchar(10)) BEGINDECLARE Stu_gradeFloat; SelectGradeIntoStu_gradeFromGradewhereStudent_no=Stu_noandCourse_no=Cour_no; IfStu_grade>=90 Then

Oracle in the database, null values are used to indicate a situation where the actual value is unknown or meaningless. In a table, if a column in a row has no value, it is called a null value (NULL). Columns of any data type can have null values if

Let's take a look at the following code to check if such an object is empty:If (someobject! = Null ){Someobject. doCalc ();}To avoid null pointer exceptions, nothing seems inappropriate. However, it is really difficult to judge whether an object in

What is a null pointer constant (null pointer constant)? [6.3.2.3-3] An integer constant expression with the value 0, or such a expression cast to type void *, is called a null p OINTER constant. This tells us: 0, 0L, ' yes ', 3-3, 0 * 17 (They are