what null

Author: JW. Zhou Date: 2014/7/2 1. NULL pointer (0/null) Returning null is equivalent to returning 0, because both null and 0 indicate null pointers. In other words, what is a null pointer is a pointer assigned 0, before initialization, the value is

Statement On the surface, the SQL statements in and exits are interchangeable and equivalent. However, they can make a big difference in processing uull data and lead to different results. The root of the problem is that in an Oracle database, a

Body: For null or empty references, most programming languages have only one value. For example, null is used in Java. However, Javascript has two special values: undefined and null. They are basically the same, but their usage is slightly different.

String.valueof the default methodargument can be null. Boolean b = null; char c = null; char[] data = null; Double d = null; float f = null; int i = NULL; Long L = null; Object obj = null; String.valueof

What are the values of null and non-null when creating a table in mysql? What are the values of null and non-null when creating a table in mysql? Mysql, I usually try not to use null. if your 0 and n mysql create a table with null values and

Now let's set the birth field of one record in the test table to null. mysql> Update test set t_birth=null where t_id=1;Query OK, 1 row affected (0.02 sec)Rows matched:1 changed:1 warnings:0 OK, execution is successful!The syntax for setting a field

1. isset function: determines whether a variable is initialized. Note: It does not determine whether the variable is null and can be used to determine whether the elements in the array have been defined.Note: When isset is used to determine whether

Several issues related to NULL values in MySQL Databases For SQL beginners, the concept of NULL value is often confusing. They often think that NULL is the same as the NULL String. This is not the case. For example, the following statements are

There is a problem at work today:In the code:1//name can be "", that is: name = = "" 2//But name is not NULL, that is: name! = NULLThe following are the differences between null and "" in Java: 1 The difference between null and "" 2 Problem One: 3

Some children who are new to MySQL often mistakenly think that NULL is the same as a NULL string. This seems unimportant, but in MySQL, the two are completely different. NULL indicates that there is no value, but it indicates that the value exists,

For SQL beginners, the concept of NULL is often confused. They often think that NULL is the same as the NULL string. This is not the case. For example, the following statements are completely different: Mysql> insert into my_table (phone) VALUES

NULL is a unique data type in the database description of NULL in Oracle NULLAbsence of a value in a column of a row. Nulls indicate missing, unknown, or inapplicable data. When a column of a record is NULL, it indicates that the value

For SQL beginners, the concept of NULL value is often confusing. They often think that NULL is the same as the NULL String. This is not the case. For example, the following statements are completely different: Mysql> insert into my_table (phone)

Author: builder.com Thursday, October 14 2004 pm On the surface, SQL statements of in and exits are interchangeable and equivalent. However, they are very different in processing uull data and lead to different results. The root cause of

PHP$test=0;if($test= = "'){ Echo' In php, 0 is empty ';//is output}if($test= = = ""){ Echo' In php, 0 is empty ';//not be output}if($test==NULL){ Echo' In php, 0 is empty ';//is output}if($test===NULL){ Echo' In php, 0 is empty ';//not be output}

 Today, when you assign the datetime type data in the database to the datetime type variable in C #, a problem occurs, that is, the datetime data in the database has a null value. C # by default, null cannot be assigned to the datetime variable,

Although the person who is proficient in SQL will not have any questions about NULL, but the whole article is still very difficult to find, see an English version, feel good. Tony Hoare invented the null reference in 1965 and considered it a

Explanation of the differences between null and "" in JavaThe difference between null and ""Question one:The difference between null and ""String S=null;String.Trim () will throw an empty exceptionString s= "";String.Trim () will not throw,

PHP tutorial PHP 0 with NULL null false difference650) this.width=650; "src=" Http://www.cdtedu.com/uploads/allimg/161017/1-16101G0595G46.png "alt=" Training "style=" border:0px; "/>The reason is that in PHP the variables are stored in the C

Today, when you assign the datetime type data in the database to the DateTime type variable in C #, a problem occurs, that is, the datetime data in the database has a null value. C # by default, null cannot be assigned to the DateTime variable, but