DAY 和 CURRENT 函数

下列查询在两个 expression 列中对 call_dtime 和 res_dtime 列返回日期（一个月中的某一天）。

图: 查询

SELECT customer_num, DAY (call_dtime), DAY (res_dtime)
          FROM cust_calls;

图: 查询结果

customer_num  (expression) (expression)
          
          106            12          12
          110             7           7
          119             1           2
          121            10          10
          127            31
          116            28          28
          116            21          27

下列查询使用 DAY 和 CURRENT 函数来将列值与当前日期（月中某日）进行比较。它只选择值比当前日期早的那些行。在此示例中，CURRENT 日是 15。

图: 查询

SELECT customer_num, DAY (call_dtime), DAY (res_dtime)
          FROM cust_calls
          WHERE DAY (call_dtime) < DAY (CURRENT);

图: 查询结果

customer_num  (expression) (expression)
            106           12           12
            110            7            7
            119            1            2
            121           10           10

下列查询使用 CURRENT 函数来选择除今天打的电话之外的所有来电。

图: 查询

SELECT customer_num, call_code, call_descr
          FROM cust_calls
          WHERE call_dtime < CURRENT YEAR TO DAY;

图: 查询结果

customer_num  106
            call_code     D
            call_descr    Order was received, but two of the cans of ANZ tennis balls
            within the case were empty
            
            customer_num  110
            call_code     L
            call_descr     Order placed one month ago (6/7) not received.
            ⋮
            customer_num  116
            call_code     I
            call_descr    Second complaint from this customer! Received two cases
            right-handed outfielder gloves (1 HRO) instead of one case
            lefties.

SYSDATE 函数与 CURRENT 函数及其类似，但当未指定 DATETIME 限定符时，其返回值的缺省精度是 DATETIME YEAR TO FRACTION(5)，而不是 CURRENT 的缺省精度 DATETIME YEAR TO FRACTION(3)。