diff --git a/docs/documentation/cn/sql-reference/sql-functions/string-functions/regexp_extract.md b/docs/documentation/cn/sql-reference/sql-functions/string-functions/regexp_extract.md
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+# regexp_extract
+
+## Syntax
+
+`VARCHAR regexp_extract(VARCHAR str, VARCHAR pattern, int pos)`
+
+## Description
+
+对字符串 str 进行正则匹配，抽取符合 pattern 的第 pos 个匹配部分。需要 pattern 完全匹配 str 中的某部分，这样才能返回 pattern 部分中需匹配部分。如果没有匹配，返回空字符串。
+
+## Examples
+
+```
+mysql> SELECT regexp_extract('AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 1);
++-------------------------------------------------------------+
+| regexp_extract('AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 1) |
++-------------------------------------------------------------+
+| b                                                           |
++-------------------------------------------------------------+
+
+mysql> SELECT regexp_extract('AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 2);
++-------------------------------------------------------------+
+| regexp_extract('AbCdE', '([[:lower:]]+)C([[:lower:]]+)', 2) |
++-------------------------------------------------------------+
+| d                                                           |
++-------------------------------------------------------------+
+```
diff --git a/docs/documentation/cn/sql-reference/sql-functions/string-functions/regexp_replace.md b/docs/documentation/cn/sql-reference/sql-functions/string-functions/regexp_replace.md
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+# regexp_replace
+
+## Syntax
+
+`VARCHAR regexp_replace(VARCHAR str, VARCHAR pattern, VARCHAR repl)
+
+## Description
+
+对字符串 str 进行正则匹配, 将命中 pattern 的部分使用 repl 来进行替换
+
+## Examples
+
+```
+mysql> SELECT regexp_replace('a b c', " ", "-");
++-----------------------------------+
+| regexp_replace('a b c', ' ', '-') |
++-----------------------------------+
+| a-b-c                             |
++-----------------------------------+
+
+mysql> SELECT regexp_replace('a b c','(b)','<\\1>');
++----------------------------------------+
+| regexp_replace('a b c', '(b)', '<\1>') |
++----------------------------------------+
+| a <b> c                                |
++----------------------------------------+
+```
diff --git a/docs/documentation/cn/sql-reference/sql-functions/string-functions/repeat.md b/docs/documentation/cn/sql-reference/sql-functions/string-functions/repeat.md
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+# repeat
+
+## Syntax
+
+`VARCHAR repeat(VARCHAR str, INT count)
+
+## Description
+
+将字符串 str 重复 count 次输出，count 小于1时返回空串，str，count 任一为NULL时，返回 NULL
+
+## Examples
+
+```
+mysql> SELECT repeat("a", 3);
++----------------+
+| repeat('a', 3) |
++----------------+
+| aaa            |
++----------------+
+
+mysql> SELECT repeat("a", -1);
++-----------------+
+| repeat('a', -1) |
++-----------------+
+|                 |
++-----------------+
+```