2.5. �ơ��֥�ؤ��䤤��碌

�ơ��֥뤫��ǡ�������Ф�����ˡ��ơ��֥���䤤��碌�򤷤ޤ��� ���Τ����SQL��SELECTʸ�����Ѥ���ޤ��� ����ʸ������ꥹ�ȡ��֤������Υꥹ����ʬ�ˤȥơ��֥�ꥹ�ȡʥǡ�������Ф��ơ��֥�Υꥹ����ʬ�ˡ�����ӡ���ά��ǽ�ʾ������¤���ꤹ����ʬ�ˤ�ʬ���뤳�Ȥ��Ǥ��ޤ��� �㤨�С�weather�����ƤιԤ���Ф��ˤϡ��ʲ������Ϥ��ޤ���

SELECT * FROM weather;

������*��"���Ƥ���"�ξ�ά���Ǥ��� [1] �������äơ��ʲ��Τ褦�ˤ��Ƥ�Ʊ����̤ˤʤ�ޤ���

SELECT city, temp_lo, temp_hi, prcp, date FROM weather;

���Ϥϡ��ʲ��Τ褦�ˤʤ�ޤ���

     city      | temp_lo | temp_hi | prcp |    date
---------------+---------+---------+------+------------
 San Francisco |      46 |      50 | 0.25 | 1994-11-27
 San Francisco |      43 |      57 |    0 | 1994-11-29
 Hayward       |      37 |      54 |      | 1994-11-29
(3 rows)

����ꥹ�Ȥˤϡ�ñ�ʤ��󻲾Ȥ����ǤϤʤ�Ǥ�դμ�����ꤹ�뤳�Ȥ��Ǥ��ޤ��� �㤨�С��ʲ���Ԥ����Ȥ��Ǥ��ޤ���

SELECT city, (temp_hi+temp_lo)/2 AS temp_avg, date FROM weather;

���η�̤ϼ��Τ褦�ˤʤ�ޤ���

     city      | temp_avg |    date
---------------+----------+------------
 San Francisco |       48 | 1994-11-27
 San Francisco |       50 | 1994-11-29
 Hayward       |       45 | 1994-11-29
(3 rows)

AS�����Ѥ���������κƥ�٥��դ�����ʬ�����դ��Ƥ������� ��AS��Ͼ�ά���뤳�Ȥ��Ǥ��ޤ��ˡ�

ɬ�פʹԤ���������ꤹ��WHERE����ɲä����䤤��碌��"����դ�"���뤳�Ȥ��Ǥ��ޤ��� WHERE��������ʿ��͡˼�����������������������Ȥʤ�ԤΤߤ��֤��ޤ��� �褯�Ȥ��������黻�ҡ�AND��OR��NOT�ˤ����դ��˻��Ѥ��뤳�Ȥ��Ǥ��ޤ��� �㤨�аʲ��ϡ�San Francisco�α�ŷ���ε��ݥǡ�������Ф��ޤ���

SELECT * FROM weather
    WHERE city = 'San Francisco' AND prcp > 0.0;

��̤ϼ��Τ褦�ˤʤ�ޤ���

     city      | temp_lo | temp_hi | prcp |    date
---------------+---------+---------+------+------------
 San Francisco |      46 |      50 | 0.25 | 1994-11-27
(1 row)

�䤤��碌�η�̤򥽡��Ȥ����֤��褦�˻��ꤹ�뤳�Ȥ��Ǥ��ޤ���

SELECT * FROM weather
    ORDER BY city;

     city      | temp_lo | temp_hi | prcp |    date
---------------+---------+---------+------+------------
 Hayward       |      37 |      54 |      | 1994-11-29
 San Francisco |      43 |      57 |    0 | 1994-11-29
 San Francisco |      46 |      50 | 0.25 | 1994-11-27

������Ǥϡ������Ƚ�Ͻ�ʬ�˻��ꤵ��Ƥ��ޤ��� �Ǥ��Τǡ�San Francisco�ιԤϽ�����ۤʤ뤫���Τ�ޤ��� �����������Τ褦�ˤ���о�˾嵭�η�̤ˤʤ�ޤ���

SELECT * FROM weather
    ORDER BY city, temp_lo;

�䤤��碌�η�̤����ʣ�Ԥ�����褦�˻��ꤹ�뤳�Ȥ��Ǥ��ޤ���

SELECT DISTINCT city
    FROM weather;

     city
---------------
 Hayward
 San Francisco
(2 rows)

�����֤��ޤ�������̹Ԥν������ư���뤫�⤷��ޤ��� DISTINCT��ORDER BY����˻��Ѥ��뤳�Ȥdzμ¤˰�Ӥ�����̤����뤳�Ȥ��Ǥ��ޤ��� [2]

SELECT DISTINCT city
    FROM weather
    ORDER BY city;

�������DISTINCT�����ORDER BY��ñ�ΤǤ���Ѥ��뤳�Ȥ��Ǥ��ޤ���