mysql根据传递的参数判断是否对语句进行UNION ALL

没有办法在语句中直接使用if条件（存储过程可以），所以可以利用下面方法实现

方法1：

SELECT *
FROM (
SELECT *, 1 as source_table
FROM hljtxeip_workday_holiday
WHERE
`year` = YEAR (
NOW())
AND `month` = MONTH (
NOW())
AND `type` = '工作日'

UNION ALL

SELECT *, 2 as source_table
FROM hljtxeip_workday_holiday
WHERE
`year` = YEAR (
NOW())
AND `month` = MONTH(DATE_SUB(NOW(), INTERVAL 1 MONTH))
AND `type` = '工作日' and 1 = 1
) AS combined_tables;

 

方法2：

SELECT *
FROM (
SELECT *, 1 as source_table
FROM hljtxeip_workday_holiday
WHERE
`year` = YEAR (
NOW())
AND `month` = MONTH (
NOW())
AND `type` = '工作日'

UNION ALL

SELECT *, 2 as source_table
FROM hljtxeip_workday_holiday
WHERE
`year` = YEAR (
NOW())
AND `month` = MONTH(DATE_SUB(NOW(), INTERVAL 1 MONTH))
AND `type` = '工作日'
) as combined_tables
WHERE (CASE WHEN 1 = 2 THEN (source_table = 1) ELSE (1 = 1) END)