Question

我想使用oracle查询从订单表中获取唯一的日期值。我正在

ORA-01791：不是SELECTed表达式

错误，当我尝试以下查询

时

SELECT DISTINCT (TO_DATE(LAST_INSERT_TIMESTAMP, 'YYYY-MM-DD HH24:MI'))
    FROM ORDER
   WHERE LAST_INSERT_TIMESTAMP IS NOT NULL
ORDER BY LAST_INSERT_TIMESTAMP DESC;

Answer 1

LAST_INSERT_TIMESTAMP不在您的结果列表中，因为您已使用DISTINCT将行汇总到截断的时间戳。你只能按此订购。

SELECT DISTINCT TRUNC(LAST_INSERT_TIMESTAMP, 'MI')
    FROM ORDER
   WHERE LAST_INSERT_TIMESTAMP IS NOT NULL
ORDER BY TRUNC(LAST_INSERT_TIMESTAMP, 'MI') DESC;

如果您不想重复表达，请使用位置排序：

ORDER BY 1 DESC;

或者为表达式使用别名：

SELECT DISTINCT TRUNC(LAST_INSERT_TIMESTAMP, 'MI') AS LAST_INSERT
    FROM ORDER
   WHERE LAST_INSERT_TIMESTAMP IS NOT NULL
ORDER BY LAST_INSERT DESC;

请注意，我已将TO_DATE替换为相应的TRUNC，因为您要做的只是截断时间戳，而不是转换为字符串和从字符串转换。

ORA-01791中的DISTINCT日期值：不是SELECTed表达式

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