Add a SELECT field to the sum Operation--nullif, IsNull, NVL function of the use of the ___ function

In the spelling of the SQL statement to do a select out of the field to sum the query, search the Internet, get some inspiration, here to write. Let's begin by introducing the function you use:

1, Nullif (ORACLE and SQL Server use the same):

Usage:

Nullif (expression1 , expression2),

Description:

If two expressions are not equal, NULLIF returns the value of the first expression1.

If two expressions are equal, NULLIF returns a null value of--null.

2, ISUNLL (only for SQL server,oracle without this function)

Usage:

ISNULL (Check_expression,replacement_value)

Description:

Check_expression: An expression that will be checked for null. Check_expression can be of any type.

Replacement_value: An expression to be returned when check_expression is null.

Note:Replacement_value must have the same type as check_expresssion.

3, NVL (only applicable to Oracle,sql server does not have this function)

Usage:

NVL (Check_expression,replacement_value)

Description:

If check_expression is null, the NVL function returns the Replacement_value value, otherwise the Check_expression value is returned, or null if two arguments are null.

Note: Check_expression and Replacement_value must be of the same data type unless you explicitly use the To_char function for type conversion.

Example:

Sum the values of the Grade1_ and grade2_ two fields in the student table:

SQL Server statement:

Select IsNull (IsNull (s.grade1_,0) +isnull (R. grade2_,0), 0) fromstudent s

Oracle Statements:

Select NVL (NVL (s.grade1_,0) +NVL (R. grade2_,0), 0) from student s

Reference URL: http://blog.sina.com.cn/s/blog_622c401d0100tz29.html