docs: add interp_clause to select syntax

docs/en/12-taos-sql/06-select.md

@@ -12,6 +12,7 @@ SELECT {DATABASE() | CLIENT_VERSION() | SERVER_VERSION() | SERVER_STATUS() | NOW
 SELECT [DISTINCT] select_list
     from_clause
     [WHERE condition]
+    [interp_clause]
     [partition_by_clause]
     [window_clause]
     [group_by_clause]
@@ -53,8 +54,11 @@ window_clause: {
   | STATE_WINDOW(col)
   | INTERVAL(interval_val [, interval_offset]) [SLIDING (sliding_val)] [WATERMARK(watermark_val)] [FILL(fill_mod_and_val)]
 
+interp_clause:
+    RANGE(ts_val, ts_val), EVERY(every_val), FILL(fill_mod_and_val)
+
 partition_by_clause:
-    PARTITION BY expr [, expr] ... 
+    PARTITION BY expr [, expr] ...
 
 group_by_clause:
     GROUP BY expr [, expr] ... HAVING condition

docs/en/12-taos-sql/10-function.md

@@ -873,9 +873,9 @@ INTERP(expr)
 - `INTERP` is used to get the value that matches the specified time slice from a column. If no such value exists an interpolation value will be returned based on `FILL` parameter.
 - The input data of `INTERP` is the value of the specified column and a `where` clause can be used to filter the original data. If no `where` condition is specified then all original data is the input.
 - `INTERP` must be used along with `RANGE`, `EVERY`, `FILL` keywords.
-- The output time range of `INTERP` is specified by `RANGE(timestamp1,timestamp2)` parameter, with timestamp1 < timestamp2. timestamp1 is the starting point of the output time range and must be specified. timestamp2 is the ending point of the output time range and must be specified.
+- The output time range of `INTERP` is specified by `RANGE(timestamp1,timestamp2)` parameter, with timestamp1 <= timestamp2. timestamp1 is the starting point of the output time range and must be specified. timestamp2 is the ending point of the output time range and must be specified.
 - The number of rows in the result set of `INTERP` is determined by the parameter `EVERY(time_unit)`. Starting from timestamp1, one interpolation is performed for every time interval specified `time_unit` parameter. The parameter `time_unit` must be an integer, with no quotes, with a time unit of: a(millisecond)), s(second), m(minute), h(hour), d(day), or w(week). For example, `EVERY(500a)` will interpolate every 500 milliseconds.
-- Interpolation is performed based on `FILL` parameter. For more information about FILL clause, see [FILL Clause](./distinguished/#fill-clause).
+- Interpolation is performed based on `FILL` parameter. For more information about FILL clause, see [FILL Clause](../distinguished/#fill-clause).
 - `INTERP` can only be used to interpolate in single timeline. So it must be used with `partition by tbname` when it's used on a STable.
 - Pseudocolumn `_irowts` can be used along with `INTERP` to return the timestamps associated with interpolation points(support after version 3.0.1.4).
 - Pseudocolumn `_isfilled` can be used along with `INTERP` to indicate whether the results are original records or data points generated by interpolation algorithm(support after version 3.0.2.3).