SQL 查询中的 if 条件

Question

我有以下SQL查询

SELECT l.LoginName ,p.name as project_name, p.start_date as 
project_start_date, p.end_date as project_end_date, 
pe.budget, pe.start_date, pe.end_date  
FROM project_expenses_new pe 
INNER JOIN projects p ON  pe.project_uuid=p.uuid 
INNER JOIN LoginUsers l ON pe.employee_uuid=l.uuid 
WHERE pe.employee_uuid='8a373382-c921-11ec-a7c7-005056020962' AND 
('2021-08-01' BETWEEN  p.start_date AND p.end_date);

基本上我使用了 3 个 table，但其中只有 2 个 table 与查询相关。这些 table 是项目，projects_expenses_new。两个 table 都有字段 start_date 和 end_date.

我想做的是检查 project_expenses_new table 中 start_date 和 end_date 的值是否具有非空值。在这种情况下，我将检查我要查找的日期是否在 project_expenses_new table 的 start_date 和 end_date 之间。因此，如果 pe.start_date 和 pe.end_date 的值不为空，则查询将为：

SELECT l.LoginName ,p.name as project_name, p.start_date as 
project_start_date, p.end_date as 
project_end_date, pe.budget, pe.start_date, pe.end_date  
FROM project_expenses_new pe 
INNER JOIN projects p ON  pe.project_uuid=p.uuid 
INNER JOIN LoginUsers l ON pe.employee_uuid=l.uuid 
WHERE pe.employee_uuid='8a373382-c921-11ec-a7c7-005056020962' AND 
('2021-08-01' BETWEEN  pe.start_date AND pe.end_date);

另一方面，如果project_expenses_new table上的start_date和end_date的值为null，我想查询条件获取记录在项目 table start_date 和 end_date 之间。这些值永远不会为 NULL。

我不确定如何在查询中加入 if 条件。

Answer 1

如果另一个日期是NULL，您可以使用IFNULL()来使用一个日期。

WHERE pe.employee_uuid = '8a373382-c921-11ec-a7c7-005056020962'
AND '2021-08-01' BETWEEN IFNULL(pe.start_date, p.start_date) AND 
                         IFNULL(pe.end_date, p.end_date)

Answer 2

如果您必须检查 start_date 和 end_date 是否都为空：

SELECT l.LoginName ,p.name as project_name, p.start_date as 
project_start_date, p.end_date as project_end_date, 
pe.budget, pe.start_date, pe.end_date  
FROM project_expenses_new pe 
INNER JOIN projects p ON  pe.project_uuid=p.uuid 
INNER JOIN LoginUsers l ON pe.employee_uuid=l.uuid 
WHERE pe.employee_uuid='8a373382-c921-11ec-a7c7-005056020962' AND 

'2021-08-01' BETWEEN (case when p.start_date is null or p.end_date is null then 
pe.p.start_date else p.start_date end) and (case when p.start_date is null or p.end_date is null then pe.p.end_date else p.end_dateend);

SQL 查询中的 if 条件

if conditions in an SQL query

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