what empty or null set

When a database field is set to NULL, the phone side will return null by default, and if I want to make the phone return empty, I have to make a judgment. 1, if I want to let the mobile phone end is empty, do not judge, table field default should be

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

In web development, there is often a need to determine whether a variable is empty (null) or an empty string (""), which affects the presentation logic of the page, and there is a corresponding method in velocity that can be judged. Of course, you

When a field in the database is set to Null, the mobile phone will return Null by default. if I want the mobile phone to return Null, I have to make a judgment. 1. if I want to leave the returned result blank on the mobile phone, I will not make any

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

In a project encountered a strange problem, it cost me a lot of time is not resolved, the final debugging found is the question of judgment-about 0 and "(empty single quotation marks, for good see I added a space), I found 0==" incredibly set up,

Encountered a strange problem in a project that cost me a lot of time without solving final debugging discovery is the question of judgment--about 0 and ' (empty single quotes, for good see I add a space) judgment, I found 0== "incredibly set up,

For beginners of SQL, the concept of null values often creates confusion, and they often assume that null is the same thing as a MySQL empty string. This is not the case. For example, the following statement is completely different:mysql> INSERT

What is an empty string and a null value:Microsoft Access can differentiate between two types of null values. Because in some cases the field is empty, it may be because the information is currently unavailable, or the field is not available for a

First, the difference between null and undefined:Executes typeof on declared but uninitialized and undeclared variables, returning "undefined".Null represents an empty object pointer, and the typeof operation returns "Object".Generally do not