GET_PATH

按 path_name 从 VARIANT 中提取值。如果任一参数为 NULL，则返回值为 Variant 或 NULL。

GET_PATH 等价于一系列 GET 函数的链式调用。path_name 由字段名的串联组成，字段名前可以带句点 (.)、冒号 (:) 或索引运算符（[index]）。第一个字段名不需要指定前导标识符。

语法

GET_PATH( <variant>, <path_name> )

参数

返回类型

VARIANT

示例

SELECT get_path(parse_json('{"k1":[0,1,2], "k2":{"k3":3,"k4":4}}'), 'k1[0]');
+-----------------------------------------------------------------------+
| get_path(parse_json('{"k1":[0,1,2], "k2":{"k3":3,"k4":4}}'), 'k1[0]') |
+-----------------------------------------------------------------------+
| 0                                                                     |
+-----------------------------------------------------------------------+

SELECT get_path(parse_json('{"k1":[0,1,2], "k2":{"k3":3,"k4":4}}'), 'k2:k3');
+-----------------------------------------------------------------------+
| get_path(parse_json('{"k1":[0,1,2], "k2":{"k3":3,"k4":4}}'), 'k2:k3') |
+-----------------------------------------------------------------------+
| 3                                                                     |
+-----------------------------------------------------------------------+

SELECT get_path(parse_json('{"k1":[0,1,2], "k2":{"k3":3,"k4":4}}'), 'k2.k4');
+-----------------------------------------------------------------------+
| get_path(parse_json('{"k1":[0,1,2], "k2":{"k3":3,"k4":4}}'), 'k2.k4') |
+-----------------------------------------------------------------------+
| 4                                                                     |
+-----------------------------------------------------------------------+

SELECT get_path(parse_json('{"k1":[0,1,2], "k2":{"k3":3,"k4":4}}'), 'k2.k5');
+-----------------------------------------------------------------------+
| get_path(parse_json('{"k1":[0,1,2], "k2":{"k3":3,"k4":4}}'), 'k2.k5') |
+-----------------------------------------------------------------------+
| NULL                                                                  |
+-----------------------------------------------------------------------+