ES 官网说，

• 超过纪元（ 1970 ）以前的日期无法使用整型表示，要用日期格式的字符串
• 可又说，内部日期都会转为整型，表示 milliseconds-since-the-epoch ==》 那这种情况，若 1970 之前的日期呢？难道是区别对待吗？分两种情况存储吗？（ 1 ） 1970 后的日期，不管啥格式都内部转整型存储 （ 2 ） 1970 前的时间，就用字符串存储

若有大佬知晓，还请不吝解释。

以下为官网原话：

• Values for milliseconds-since-the-epoch must be non-negative. Use a formatted date to represent dates before 1970.
• Internally, dates are converted to UTC (if the time-zone is specified) and stored as a long number representing milliseconds-since-the-epoch.
• Queries on dates are internally converted to range queries on this long representation, and the result of aggregations and stored fields is converted back to a string depending on the date format that is associated with the field.
• Dates will always be rendered as strings, even if they were initially supplied as a long in the JSON document.