Oracle_NVL函数

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NVL

Syntax

Description of the illustration nvl.gif

Purpose

NVL lets you replace null (returned as a blank) with a string in the results of a query. Ifexpr1 is null, thenNVL returnsexpr2. Ifexpr1 is not null, thenNVL returnsexpr1.

The arguments expr1 and expr2 can have any data type. If their data types are different, then Oracle Database implicitly converts one to the other. If they cannot be converted implicitly, then the database returns an error. The implicit conversion is implemented as follows:

• If expr1 is character data, then Oracle Database convertsexpr2 to the data type ofexpr1 before comparing them and returnsVARCHAR2 in the character set ofexpr1.

• If expr1 is numeric, then Oracle Database determines which argument has the highest numeric precedence, implicitly converts the other argument to that data type, and returns that data type.

  See Also:

  • Table 3-10, "Implicit Type Conversion Matrix" for more information on implicit conversion and"Numeric Precedence" for information on numeric precedence

  • "COALESCE" and"CASE Expressions", which provide functionality similar to that of NVL

Examples

The following example returns a list of employee names and commissions, substituting "Not Applicable" if the employee receives no commission:

SELECT last_name, NVL(TO_CHAR(commission_pct), 'Not Applicable') commission
  FROM employees
  WHERE last_name LIKE 'B%'
  ORDER BY last_name;
 
LAST_NAME                 COMMISSION
------------------------- ----------------------------------------
Baer                      Not Applicable
Baida                     Not Applicable
Banda                     .1
Bates                     .15
Bell                      Not Applicable
Bernstein                 .25
Bissot                    Not Applicable
Bloom                     .2
Bull                      Not Applicable

 

SQL> create table testNVL(          
  2   id number,
  3   tName varchar2(20) 
  4  );

Table created.

 

SQL> insert into testnvl(id,tname) values(1,'1');

1 row created.

SQL> insert into testnvl(id) values(2);

1 row created.

SQL> insert into testnvl(tname) values('3');

1 row created.

SQL> insert into testnvl(id,tname) values('4','4');

1 row created.

SQL> select id,tname from testnvl;

        ID TNAME
---------- --------------------
         1 1
         2
           3
         4 4

 

 

SQL> select id,tname from testnvl;

        ID TNAME
---------- --------------------
         1 1
         2
           3
         4 4

SQL> select id,nvl(id,10*id),tname from testnvl;

        ID NVL(ID,10*ID) TNAME
---------- ------------- --------------------
         1             1 1
         2             2
                         3
         4             4 4

SQL> select id,tname,nvl(tname,10*tname) from testnvl;

        ID TNAME                NVL(TNAME,10*TNAME)
---------- -------------------- ----------------------------------------
         1 1                    1
         2
           3                    3
         4 4                    4

SQL> select id,nvl(id,'is null'),tname from testnvl;
select id,nvl(id,'is null'),tname from testnvl
                 *
ERROR at line 1:
ORA-01722: invalid number


SQL> select id,tname,nvl(tname,'is null') from testnvl;

        ID TNAME                NVL(TNAME,'ISNULL')
---------- -------------------- --------------------
         1 1                    1
         2                      is null
           3                    3
         4 4                    4

SQL> select id,nvl(to_char(id),'is null'),tname from testnvl;

        ID NVL(TO_CHAR(ID),'ISNULL')                TNAME
---------- ---------------------------------------- --------------------
         1 1                                        1
         2 2
           is null                                  3
         4 4                                        4