SQL Example 9--group, having

<title>SQL Example 9–group, having</title> SQL Example 9–group, having

• Group
  
  • SQL Create
    
  • SQL Delete
    
  • SQL Select
    

  TruncateTableUser1;Insert  intoUser1 (ID, username)Values(1,' test1 ');Insert  intoUser1 (ID, username)Values(2,' test1 ');Insert  intoUser1 (ID, username)Values(3,' test1 ');Insert  intoUser1 (ID, username)Values(4,' test1 ');Insert  intoUser1 (ID, username)Values(5,' test1 ');Insert  intoUser1 (ID, username)Values(1,' Test2 ');Insert  intoUser1 (ID, username)Values(2,' Test2 ');Insert  intoUser1 (ID, username)Values(3,' Test2 ');Insert  intoUser1 (ID, username)Values(4,' Test2 ');Insert  intoUser1 (ID, username)Values(5,' Test2 ');Insert  intoUser1 (ID, username)Values(1,' Test3 ');Insert  intoUser1 (ID, username)Values(2,' Test3 ');Insert  intoUser1 (ID, username)Values(3,' Test3 ');Insert  intoUser1 (ID, username)Values(4,' Test3 ');Insert  intoUser1 (ID, username)Values(5,' Test3 ');

  Select  from Group  by username;

  | ID | Username |+----+----------+|  1 | Test1    | |  1 | Test2    | |  1 | Test3    |

Select  from Group  by ID;

| ID | Username |+----+----------+|  1 | Test1    | |  2 | Test1    | |  3 | Test1    | |  4 | Test1    | |  5 | Test1    |

Grouping is actually asking for a collection?

Select  from Group  by 1;

1 refers to the username, group by 2 refers to the ID (generally not used, good ugly usage)

• Having
  Equivalent to where
  

  Select  from Group  by ID;

  | Username | ID |+----------+----+| Test1    |  1 | | Test1    |  2 | | Test1    |  3 | | Test1    |  4 | | Test1    |  5 |

  Select  from Group  by  having inch (1, 2, 3);

  | Username | ID |+----------+----+| Test1    |  1 | | Test1    |  2 | | Test1    |  3 |

  Select  from Group  by  having inch (1, 2, 3);

  Select  from Group  by  having inch (1, 2, 3);   # error, no ID this field

SQL Example 9--group, having