add zh/en docs

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

@@ -867,10 +867,16 @@ FIRST(expr)
 ### INTERP
 
 ```sql
-INTERP(expr)
+INTERP(expr [, ignore_null_values])
+
+ignore_null_values: {
+    0
+  | 1
+}
 ```
 
-**Description**: The value that matches the specified timestamp range is returned, if existing; or an interpolation value is returned.
+**Description**: The value that matches the specified timestamp range is returned, if existing; or an interpolation value is returned. The value of `ignore_null_values` can be 0 or 1, 1 means null values are ignored. The default value of this parameter is 0.
+
 
 **Return value type**: Same as the column being operated upon
 

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

@@ -869,10 +869,15 @@ FIRST(expr)
 ### INTERP
 
 ```sql
-INTERP(expr)
+INTERP(expr [, ignore_null_values])
+
+ignore_null_values: {
+    0
+  | 1
+}
 ```
 
-**功能说明**：返回指定时间截面指定列的记录值或插值。
+**功能说明**：返回指定时间截面指定列的记录值或插值。ignore_null_values 参数的值可以是 0 或 1，为 1 时表示忽略 NULL 值, 缺省值为0。
 
 **返回数据类型**：同字段类型。