需要帮助使用 WHERE 编写查询

Question

编写查询以显示所有男性员工的员工编号、员工全名、专业 id。

SELECT staffid, firstname, lastname, specid, specname 
  FROM staff, staffspeciality, speciality     
 WHERE speciality.specid = staff_speciality.specid     
 WHERE staff.staffid = staff_speciality.staffid     
 WHERE gender = ‘M’;

SQL> 描述员工

Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 STAFFID                                   NOT NULL CHAR(2)
 FIRSTNAME                                          VARCHAR2(20)
 LASTNAME                                           VARCHAR2(20)
 ROLE                                               VARCHAR2(15)
 GENDER                                             CHAR(1)
 DATEJOINED                                         DATE
 DATELEFT                                           DATE

SQL> 描述专业；

 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 SPECIALID                                 NOT NULL CHAR(4)
 SPECNAME                                           VARCHAR2(20)
 SPECNOTES                                          VARCHAR2(100)

SQL> 描述员工专业；

 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 STAFFID                                   NOT NULL CHAR(2)
 SPECID                                    NOT NULL CHAR(4)
 DATEQUALIFIED                             NOT NULL DATE
 VALIDTILLDATE                                      DATE
 DETAILS                                            VARCHAR2(100)

Answer 1

像这样：

SELECT staff.staffid, staff.firstname, staff.lastname, staff_speciality.specid, speciality.specname 
  FROM staff 
  JOIN staff_speciality
    ON staff.staffid = staff_speciality.staffid   
  JOIN speciality     
    ON speciality.specid = staff_speciality.specid         
 WHERE gender = ‘M’;