substring_index
Name
SUBSTRING_INDEX
description
Syntax
VARCHAR substring_index(VARCHAR content, VARCHAR delimiter, INT field)
返回 content 的子字符串，在 delimiter 出现 field 次的位置按如下规则截取：
如果 field > 0，则从左边算起，返回截取位置前的子串；
如果 field < 0，则从右边算起，返回截取位置后的子串；
如果 field = 0，返回一个空串（content 不为 null）, 或者 Null（content = null）。
- delimiter 大小写敏感，且是多字节安全的。
delimiter和field参数需要是常量，不支持变量。
example
mysql> select substring_index("hello world", " ", 1);
+----------------------------------------+
| substring_index("hello world", " ", 1) |
+----------------------------------------+
| hello |
+----------------------------------------+
mysql> select substring_index("hello world", " ", 2);
+----------------------------------------+
| substring_index("hello world", " ", 2) |
+----------------------------------------+
| hello world |
+----------------------------------------+
mysql> select substring_index("hello world", " ", -1);
+-----------------------------------------+
| substring_index("hello world", " ", -1) |
+-----------------------------------------+
| world |
+-----------------------------------------+
mysql> select substring_index("hello world", " ", -2);
+-----------------------------------------+
| substring_index("hello world", " ", -2) |
+-----------------------------------------+
| hello world |
+-----------------------------------------+
mysql> select substring_index("hello world", " ", -3);
+-----------------------------------------+
| substring_index("hello world", " ", -3) |
+-----------------------------------------+
| hello world |
+-----------------------------------------+
mysql> select substring_index("hello world", " ", 0);
+----------------------------------------+
| substring_index("hello world", " ", 0) |
+----------------------------------------+
| |
+----------------------------------------+keywords
SUBSTRING_INDEX, SUBSTRING