Merge pull request #1246 from taosdata/feature/lihui

[add describe for the timestamp of insert the oldest and earliest rec…

documentation/webdocs/markdowndocs/TAOS SQL-ch.md

@@ -191,9 +191,10 @@ TDengine缺省的时间戳是毫秒精度，但通过修改配置参数enableMic
     ```
     同时向表tb1_name和tb2_name中按列分别插入多条记录 
 
-注意：对同一张表，插入的新记录的时间戳必须递增，否则会跳过插入该条记录。如果时间戳为0，系统将自动使用服务器当前时间作为该记录的时间戳。
+注意：1、对同一张表，插入的新记录的时间戳必须递增，否则会跳过插入该条记录。如果时间戳为0，系统将自动使用服务器当前时间作为该记录的时间戳。
+      2、允许插入的最老记录的时间戳，是相对于当前服务器时间，减去配置的keep值（数据保留的天数），允许插入的最早记录的时间戳，是相对于当前服务器时间，加上配置的days值（数据文件存储数据的时间跨度，单位为天）。keep和days都是可以在创建数据库时指定的，缺省值分别是3650天和10天。
 
-**IMPORT**：如果需要将时间戳小于最后一条记录时间的记录写入到数据库中，可使用IMPORT替代INSERT命令，IMPORT的语法与INSERT完全一样。如果同时IMPORT多条记录，需要保证一批记录是按时间戳排序好的。
+**IMPORT**：如果需要将时间戳小于最后一条记录时间的记录写入到数据库中，可使用IMPORT替代INSERT命令，IMPORT的语法与INSERT完全一样。
 
 ## 数据查询
 

documentation/webdocs/markdowndocs/TAOS SQL.md

@@ -181,9 +181,10 @@ All the keywords in a SQL statement are case-insensitive, but strings values are
                 tb2_name (tb2_field1_name, ...) VALUES(field1_value1, ...) (field1_value2, ...)
     ```
 
-Note: For a table, the new record must have a timestamp bigger than the last data record, otherwise, it will be discarded and not inserted. If the timestamp is 0, the time stamp will be set to the system time on the server.
-
-**IMPORT**: If you do want to insert a historical data record into a table, use IMPORT command instead of INSERT. IMPORT has the same syntax as INSERT. If you want to import a batch of historical records, the records must be ordered by the timestamp, otherwise, TDengine won't handle it in the right way.
+Note: 1. For a table, the new record must have a timestamp bigger than the last data record, otherwise, it will be discarded and not inserted. If the timestamp is 0, the time stamp will be set to the system time on the server.
+      2.The timestamp of the oldest record allowed to be inserted is relative to the current server time, minus the configured keep value (the number of days the data is retained), and the timestamp of the earliest record allowed to be inserted is relative to the current server time, plus the configured days value (the time span in which the data file stores data, in days). Both keep and days can be specified when creating the database. The default values are 3650 days and 10 days, respectively.
+ 
+**IMPORT**: If you do want to insert a historical data record into a table, use IMPORT command instead of INSERT. IMPORT has the same syntax as INSERT. 
 
 ## Data Query