Question

我有假日表，其中包含以下字段

COLUMN_NAME         DATA_TYPE
-------------------------------
HOLIDAY_ID          NUMBER(10,0)
HOLIDAY_NAME        VARCHAR2(150 BYTE)
HOLIDAY_DATE        TIMESTAMP(6)
DAY_OF_WEEK         VARCHAR2(20 BYTE)
HOLIDAY_TYPE_ID     NUMBER

，样本数据为

HOLIDAY_ID   HOLIDAY_NAME     HOLIDAY_DATE                      DAY_OF_WEEK     HOLIDAY_TYPE_ID
-------------------------------------------------------------------------------
305         Republic Day      26-01-17 12:00:00.000000000 AM    Thursday         1

306         Maha Shivratri    24-02-17 12:00:00.000000000 AM     Friday          1

我使用以下查询来获取特定月/年的holiday_date：的 （QUERY）

select nvl((select to_char(holiday_date,'DD/MM/YY') holiday 
from admin_holiday where to_char(holiday_date,'DD-MON-YYYY') like '%-JUN-2016%' 
and holiday_type_id=1 and to_char(holiday_date,'Day') not like 'Sun%' 
and to_char(holiday_date,'Day') not like 'Sat%'),'0') holiday from dual

如果结果为null（即月份/年= JUN / 2016），则此工作正常但当月份包含多个假期（即月份/年份）时，“单行子查询返回多行”错误= 2016年10月）

如何编写查询，如果查询返回多行，则显示那些结果，否则显示“0”表示NULL结果？

[注意：假期符合印度日历]

Answer 1

您应该考虑将查询更改为：

SELECT NVL(TO_CHAR(holiday_date,'DD/MM/YY'), '0') holiday
FROM admin_holiday 
WHERE TO_CHAR(holiday_date,'MON-YYYY') = 'JUN-2016' 
--WHERE TO_CHAR(holiday_date,'yyyymm') = '201606'
    AND holiday_type_id = 1 
    AND TO_CHAR(holiday_date,'Day') NOT IN ('Sun', 'Sat');

Answer 2

您需要将nvl函数应用于列，结果如下：

select nvl(to_char(holiday_date,'DD/MM/YY'),'0') holiday 
from (select 1 as dummy from dual) d left join admin_holiday 
on to_char(holiday_date,'DD-MON-YYYY') like '%-JUN-2016%' 
and holiday_type_id=1 and to_char(holiday_date,'Day') not like 'Sun%' 
and to_char(holiday_date,'Day') not like 'Sat%'

旁注：了解如何撰写sargable queries

Answer 3

SELECT NVL(TO_CHAR(holiday_date,'DD/MM/YY'), '0') holiday
FROM admin_holiday 
WHERE TO_CHAR(holiday_date,'MON-YYYY') = 'JUN-2016' 
--WHERE TO_CHAR(holiday_date,'yyyymm') = '201606'
    AND holiday_type_id = 1 
    AND TO_CHAR(holiday_date,'Day') NOT IN ('Sun', 'Sat')
union all
select '0' from dual where not exists(SELECT NVL(TO_CHAR(holiday_date,'DD/MM/YY'), '0') holiday
FROM admin_holiday 
WHERE TO_CHAR(holiday_date,'MON-YYYY') = 'JUN-2016' 
--WHERE TO_CHAR(holiday_date,'yyyymm') = '201606'
    AND holiday_type_id = 1 
    AND TO_CHAR(holiday_date,'Day') NOT IN ('Sun', 'Sat'))

查询从单个查询中获取多个结果或返回null

3 个答案: