comparing null values in sql

Label: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 only use VB in the Is

Label:There are three ways to replace null values in query results in SQL Server. If you have one of the following tables: We can use self-connect (self-join) as a table of employee name and its corresponding manager name: SELECT E. [name], M.[name]from [ Tblemployee] as E leftJOIN[ Tblemployee] as M on= M.employeeid We can see that Todd's corresponding Ma

SQL 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 false.SQL handling of query filtering conditions: Accept Ture deny false and unknownSQL handling of CHECK constraints: Accept FALSE deny TRUE and UNKnown the subtlety of unknown is when it is reversed results are still unknown ,

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 false.SQL handling of query filtering conditions: Accept Ture deny false and unknownSQL handling of CHECK constraints: Accept FALSE deny TRUE and UNKnown

The table structure is created like the following code Copy Code code as follows: CREATE TABLE TEST_TB ( TestID int NOT null identity (1,1) primary key, Caption nvarchar (MB) null ); Go Solution 1: The first idea for this question may be: Is it OK to add a unique key to the caption field? OK, let's follow this thread and create a unique index first. Copy Code code as

Solution 1: for this problem, the first thought may be: Can I add a unique key to the caption field? Well, let's proceed with this idea and create a unique index first. Nbsp; Code: createuniquenonclusteredindexun_test_tbontest_tb (caption) go index has been created. Let's test the effect nbsp; Code: I solution 1: For this question, the first thought may be: Can I add a unique key to the caption field? Well, let's proceed with this idea and create a unique index first. The Code is as follows: C

Sometimes the following error occurs when you create a SQL Server job with an SQL statement: MSG 515, Level 16, State 2, procedure sp_add_job, line 137th Cannot insert value NULL into column ' owner_sid ', table ' msdb.dbo.sysjobs '; column does not allow null values