【练习】简单函数2

 nvl（A，B）当A为空时就返回B；
nvl2(A,B,C)当A不为空返回B，A为空时返回C
nullif（A,B）当A和B相等时返回空，不等时返回A                                          
coalese（A,B,C,D）返回参数中第一个非空的 

1.使用nvl函数

SQL> SELECT last_name, salary, NVL(commission_pct, 0),
   (salary*12) + (salary*12*NV  2  L(commission_pct, 0)) AN_SAL
FROM employees;
  3  
LAST_NAME                     SALARY NVL(COMMISSION_PCT,0)     AN_SAL
------------------------- ---------- --------------------- ----------
OConnell                        2600                     0      31200
Grant                           2600                     0      31200
Whalen                          4400                     0      52800
Hartstein                      13000                     0     156000
Fay                             6000                     0      72000
Mavris                          6500                     0      78000
Baer                           10000                     0     120000
Higgins                        12008                     0     144096
Gietz                           8300                     0      99600
King                           24000                     0     288000
Kochhar                        17000                     0     204000

2.使用nvl2函数

SQL> SELECT last_name,  salary, commission_pct,
       NVL2(commission_pct, 
          2    3      'SAL+COMM', 'SAL') income
FROM   employees WHERE department_id IN (50, 80);
  4  
LAST_NAME                     SALARY COMMISSION_PCT INCOME
------------------------- ---------- -------------- --------
OConnell                        2600                SAL
Grant                           2600                SAL
Weiss                           8000                SAL
Fripp                           8200                SAL
Kaufling                        7900                SAL
Vollman                         6500                SAL
Mourgos                         5800                SAL
Nayer                           3200                SAL
Mikkilineni                     2700                SAL
Landry                          2400                SAL
Markle                          2200                SAL

3.使用nullif函数

SQL> SELECT first_name, LENGTH(first_name) "expr1",              
       last_name,  LENGTH(last_n  2  ame)  "expr2",
       NULLIF(LENGTH(first_name), LENGTH(last_name)) result
FROM   employees;
  3    4  
FIRST_NAME                expr1 LAST_NAME                      expr2     RESULT
-------------------- ---------- ------------------------- ---------- ----------
Ellen                         5 Abel                               4          5
Sundar                        6 Ande                               4          6
Mozhe                         5 Atkinson                           8          5
David                         5 Austin                             6          5
Hermann                       7 Baer                               4          7
Shelli                        6 Baida                              5          6
Amit                          4 Banda                              5          4
Elizabeth                     9 Bates                              5          9
Sarah                         5 Bell                               4          5
David                         5 Bernstein                          9          5
Laura                         5 Bissot                             6          5

4.使用 COALESCE 函数

SQL> SELECT last_name, employee_id,
COALESCE(TO_CHAR(commission_pct),TO_CHAR(manager_  2  id),
        'No commission and no manager') 
FROM employees;
  3    4  
LAST_NAME                 EMPLOYEE_ID COALESCE(TO_CHAR(COMMISSION_PCT),TO_CHAR
------------------------- ----------- ----------------------------------------
OConnell                          198 124
Grant                             199 124
Whalen                            200 101
Hartstein                         201 100
Fay                               202 201
Mavris                            203 101
Baer                              204 101
Higgins                           205 101
Gietz                             206 205
King                              100 No commission and no manager
Kochhar                           101 100