sql null value

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

The environment of the program is VB6 + ADO + Access, when you query with SQL statements, you want to combine two fields into one field, but one of the null values in one field directly causes two fields to merge and become null values. Before can

The introduction of 1null value NULL is a unique data type in the database. When 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

Detailed description of the null value in the database language, detailed description of the null value in the database Although those who are familiar with SQL do not have any questions about Null, it is still difficult to find a well-summarized

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

Transferred from: http://www.maomao365.com/?p=6965Summary:Here are two ways to share a null value in a field with a specified value, as follows:Lab environment: SQL Server R2 Cases:Create TableTest (keyIdint Identity, infovarchar( -))GoInsert

1.NULL meaning is the missing value (missing value).2. Three value logic (Three-valued-logic:true,false,unknown). There are three logical predicates in SQL: Ture,false,unknown. In most programming language only True and false in SQL , and all of the

Original: null value problem in SQL ServerSQL uses three-valued predicate logic, so the result returned by a logical expression can be true, false, or unknown, and returning true in the three-value logic is not exactly the same as not returning

In the previous article, we had a glimpse of NULL, the incredible little thing. Today, I introduce it as much as I can. By convention, this is a discussion that is as simple as possible but not rigorous, and may even be less serious. My goal is to

Null and SQLnull in SQL A summary of null in Oracle SQL is as follows:1.1 null The null value is still null. Null is an unallocated, unknown, or not applicable value. Ø null is neither 0 nor a space.  1.1.1 null Value Calculation The result of the