comparing null values in sql

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 (

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) VALUES (

operation:SELECT * from emp order by comm DESC;4) ORACLE's NULL and any value arithmetic operations result in NULL# Addition, subtraction, multiplication, division:SELECT 1 + null from dual;SELECT 1-null from dual;SELECT 1 * null from dual;SELECT 1/

VARCHAR2 (20): = 'a ';BEGINIF n1 Dbms_output.put_line ('ELSEDbms_output.put_line ('= ');End if;END; Output: = 6) work, especially in report development. In SQL statements involving quantity and amount statistics, the NVL function is used to ignore NULL values. 4. Usage of related NULL functions:1) NVL (p1, p2) functio

The impact of indexes and Null values on Hints and execution plans because B * Tree indexes do not store Null values, some Oracle queries are allowed when the index field is Null.If you do not use Index. www.2cto.com many times, it seems that you can use Full Index Scan.The index is dropped because the

the clustered index table USE Test; GO DROPTABLE TEST; GO CREATETABLE TEST (OBJECT_ID INT, NAME VARCHAR(12), AGE INT); CREATECLUSTEREDINDEX PK_TEST ON TEST(OBJECT_ID) DECLARE @IndexINT =0; WHILE @Index BEGIN INSERT INTO TEST SELECT @Index, 'kerry'+ CAST(@IndexASVARCHAR), floor(rand()*100) ; SET @Index = @Index +1; END INSERT INTO TEST SELECT 10001, 'NULL', 12 UNIONALL SELECT 10002, '

Tags: implement server return prompt control configuration apply value spaceThese two types of notation are often encountered: is not NULL and!=null. It is also often encountered that the database has data that meets the criteria!=null, but is returned as an empty collection. In fact, the difference between the two uses is not understood. By default, it is recomm

Today, I used Entity Framework to rewrite an earlier project. When it involved processing null values, I encountered a problem: how to query records with a null field in the database, I wrote several examples for testing and then used SQL Server Profiler to capture SQL. T

';BEGINIF n1 Dbms_output.put_line ('ELSEDbms_output.put_line ('= ');End if;END;Output: =6) work, especially in report development. In SQL statements involving quantity and amount statistics, the NVL function is used to ignore NULL values.4. Usage of related NULL functions:1) NVL (p1, p2) function. If p1 is

operator such as =, DECLAREN1 VARCHAR2 (20);N2 VARCHAR2 (): = ' a ';BEGINIF N1 Dbms_output.put_line (' ELSEDbms_output.put_line (' = ');END IF;END; Output: = 6) in the work. Especially in report development. In SQL statements involving quantity, amount statistics, and so on, the NVL function is used to ignore null values. 4, the related

Is not null and! in SQL! = NULL difference, sqlnull These two methods are often used: is not null and! = NULL. We often encounter database conditions! = NULL, but the returned result is a NULL