时间戳..只需要第一个和最后一个

Question

我有一个查询返回估计的日期和时间戳。每个估算可以有多个时间戳。我只需要第一张和最后一张邮票。我怎样才能做到这一点？我的查询是这样的：

SELECT LogDateTime, Operator, Program, Explanation, TransactionCode 
FROM SystemLog 
WHERE Program = 'Estimating' 
ORDER BY TransactionCode 

Answer 1

使用min()和max()聚合函数：

SELECT 
    min(LogDateTime) as first_LogDateTime, 
    max(LogDateTime) as last_LogDateTime, 
    Operator, Program, Explanation, TransactionCode 
FROM SystemLog 
WHERE Program = 'Estimating' 
GROUP BY Operator, Program, Explanation, TransactionCode 
ORDER BY TransactionCode