Add FORMAT_BYTES and FORMAT_NANO_TIME functions (pingcap#20518) (pingcap#20519)

Author: ti-chi-bot

TOC.md

@@ -950,12 +950,13 @@
       - [GROUP BY 聚合函数](/functions-and-operators/aggregate-group-by-functions.md)
       - [GROUP BY 修饰符](/functions-and-operators/group-by-modifier.md)
       - [窗口函数](/functions-and-operators/window-functions.md)
+      - [序列函数](/functions-and-operators/sequence-functions.md)
+      - [效用函数](/functions-and-operators/utility-functions.md)
       - [其它函数](/functions-and-operators/miscellaneous-functions.md)
+      - [TiDB 特有的函数](/functions-and-operators/tidb-functions.md)
       - [精度数学](/functions-and-operators/precision-math.md)
       - [集合运算](/functions-and-operators/set-operators.md)
-      - [序列函数](/functions-and-operators/sequence-functions.md)
-      - [下推到 TiKV 的表达式列表](/functions-and-operators/expressions-pushed-down.md)
-      - [TiDB 特有的函数](/functions-and-operators/tidb-functions.md)
+      - [下推到 TiKV 的表达式列表](/functions-and-operators/expressions-pushed-down.md)          
       - [Oracle 与 TiDB 函数和语法差异对照](/oracle-functions-to-tidb.md)
     - [聚簇索引](/clustered-indexes.md)
     - [约束](/constraints.md)

functions-and-operators/utility-functions.md

@@ -0,0 +1,42 @@
+---
+title: 效用函数
+summary: 了解 TiDB 中的效用函数。
+---
+
+# 效用函数
+
+本文介绍了 TiDB 支持的效用函数，这些函数旨在简化常见数据转换，使结果更易于阅读和理解。
+
+## `FORMAT_BYTES()`
+
+`FORMAT_BYTES()` 函数用于将字节数格式化为易于阅读的形式。
+
+```sql
+SELECT FORMAT_BYTES(10*1024*1024);
+```
+
+```
++----------------------------+
+| FORMAT_BYTES(10*1024*1024) |
++----------------------------+
+| 10.00 MiB                  |
++----------------------------+
+1 row in set (0.001 sec)
+```
+
+## `FORMAT_NANO_TIME()`
+
+`FORMAT_NANO_TIME()` 函数用于将纳秒数格式化为易于阅读的时间形式。
+
+```sql
+SELECT FORMAT_NANO_TIME(1000000);
+```
+
+```
++---------------------------+
+| FORMAT_NANO_TIME(1000000) |
++---------------------------+
+| 1.00 ms                   |
++---------------------------+
+1 row in set (0.001 sec)
+```