docs: update default trigger mode

docs/en/12-taos-sql/14-stream.md

@@ -108,7 +108,7 @@ SHOW STREAMS;
 
 When you create a stream, you can use the TRIGGER parameter to specify triggering conditions for it.
 
-For non-windowed processing, triggering occurs in real time. For windowed processing, there are three methods of triggering:
+For non-windowed processing, triggering occurs in real time. For windowed processing, there are three methods of triggering，the default value is AT_ONCE:
 
 1. AT_ONCE: triggers on write
 

docs/zh/12-taos-sql/14-stream.md

@@ -114,7 +114,7 @@ SELECT * from information_schema.`ins_streams`;
 
 在创建流时，可以通过 TRIGGER 指令指定流式计算的触发模式。
 
-对于非窗口计算，流式计算的触发是实时的；对于窗口计算，目前提供 3 种触发模式：
+对于非窗口计算，流式计算的触发是实时的；对于窗口计算，目前提供 3 种触发模式，默认为 AT_ONCE：
 
 1. AT_ONCE：写入立即触发