select if not null

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

One thousand reasons for not using Null, Null Hong Kong, Null seems to be a headache everywhere. For example, NullPointerException, which is a headache in Java, in order to avoid the unexpected Null pointer exception, for thousands of years,

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

In fact, there is nothing to say about this problem, today's optimization encountered an SQL statement, because it is more interesting, so I intercepted, simplified the SQL statement, to show you, as shown belowDECLARE @bamboo_Code varchar (3);Set

Http://boylook.itpub.net/post/43144/520538 The ocp SQL section has the following question: You need to add a not null constraint to the QUANTITY column in the PO_DETAIL table. Which statement shocould you use to complete this task? Correct A. alter

Believe that a lot of people who have been using MySQL for a long time, the concept of these two field properties is not very clear, the general will have the following questions: My field type is not NULL, why can I insert a null value

Is null and is not null in SQL SERVER cause index failure ?, Sqlnull In fact, there is nothing to say about this problem. I encountered an SQL statement during optimization today. Because it is interesting, I have cut and simplified the SQL

Differences between null and not null in mysql and efficiency issues Mysql users may encounter the following situations: 1. My field type is not null. Why can I insert null values? 2. Why is not null more efficient than null? 3. When determining

In mysql, null, not null, default, and auto_increment are common content. Here I will detail the usage of null, not null, default, and auto_increment in msyql. NULL and not null modifiers: You can add the NULL or not null modifier after each field