add new doc of locate(matrixorigin#874)

docs/MatrixOne/Reference/Functions-and-Operators/String/locate.md

@@ -0,0 +1,73 @@
+# **LOCATE()**
+
+## **函数说明**
+
+`LOCATE()` 函数是用于在字符串中查找子字符串所在位置的函数。它返回子字符串在字符串中的位置，如果未找到，则返回 0。
+
+由于 `LOCATE()` 函数返回的是一个整数值，所以它可以嵌套在其他函数里面使用，比如可以用 substring 函数截取字符串。
+
+关于大小写，`LOCATE()` 函数不区分大小写。
+
+## **函数语法**
+
+```
+> LOCATE(subtr,str,pos)
+```
+
+## **参数释义**
+
+|  参数   | 说明  |
+|  ----  | ----  |
+| substr | 必要参数。`substring` 是你正在查找的字符串。|
+| str | 必要参数。`string` 是要在其中搜索的字符串。|
+| pos | 非必要参数。`position` 是表示开始查询的位置。|
+
+## **示例**
+
+- 示例 1
+
+```sql
+mysql> SELECT LOCATE('bar', 'footbarbar');
++-------------------------+
+| locate(bar, footbarbar) |
++-------------------------+
+|                       5 |
++-------------------------+
+1 row in set (0.00 sec)
+```
+
+- 示例 2
+
+```sql
+mysql>SELECT LOCATE('bar', 'footbarbar',6);
++----------------------------+
+| locate(bar, footbarbar, 6) |
++----------------------------+
+|                          8 |
++----------------------------+
+1 row in set (0.00 sec)
+```
+
+- 示例 3
+
+```sql
+mysql>SELECT SUBSTRING('hello world',LOCATE('o','hello world'),5);
++---------------------------------------------------+
+| substring(hello world, locate(o, hello world), 5) |
++---------------------------------------------------+
+| o wor                                             |
++---------------------------------------------------+
+1 row in set (0.00 sec)
+```
+
+- 示例 4
+
+```sql
+mysql>select locate('a','ABC');
++----------------+
+| locate(a, ABC) |
++----------------+
+|              1 |
++----------------+
+1 row in set (0.00 sec)
+```

mkdocs.yml

@@ -502,6 +502,7 @@ nav:
             - INSTR():  MatrixOne/Reference/Functions-and-Operators/String/instr.md
             - LEFT(): MatrixOne/Reference/Functions-and-Operators/String/left.md
             - LENGTH(): MatrixOne/Reference/Functions-and-Operators/String/length.md
+            - LOCATE(): MatrixOne/Reference/Functions-and-Operators/String/locate.md
             - LOWER(): MatrixOne/Reference/Functions-and-Operators/String/lower.md
             - LPAD(): MatrixOne/Reference/Functions-and-Operators/String/lpad.md
             - LTRIM(): MatrixOne/Reference/Functions-and-Operators/String/ltrim.md