text: -- @testpoint: json操作符：->>获得 JSON 数组元素，下标不存在返回空。输入不合理时，合理报错
  
  --合理输入：左侧输入值为array-json类型，右侧为int类型
  select '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json ->> 0;
  select '["a","foo","b","bar","c","baz"]'::json ->> 2.1;
  select '["a","foo","b","bar","c","baz"]'::json ->> 2.7;
  select '[null,true,false,"null","true","false"]'::json ->> -5.5;
  select '[138,0.58,-369,1.25e+6]'::json ->> 1/3;
  
  --合理输入2.左侧输入键的值为空的array-json类型，右侧为int类型
  select '[]'::json ->> 0;
  select '[""]'::json ->> 1;
  select '[null]'::json ->> 2;
  
  --合理输入3.左侧输入值为array-json类型，右侧为可隐式转换为int类型的类型
  select '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json ->> true;
  select '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json ->> false;
  select '[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json ->> null;
  
  --不合理输入1.左侧输入值为array-json类型，右侧为非int类型
  select '["a","foo","b","bar","c","baz"]'::json ->> "b" ;
  select '[null,true,false,"null","true","false"]'::json ->> 2021-05-31 12:59:08;
  select '[138,0.58,-369,1.25e+6]'::json ->> 192.168.100.128/25;
  
  --不合理输入2.左侧输入值为非array-json类型，右侧为int类型
  select '138'::json ->> 1;
  select '"ALL"'::json ->> 0;
  select '+100'::json ->> -2;
  select 'null'::json ->>2;
  select 'true'::json ->8;
  
  --不合理输入3.左侧输入值为非array-json类型，右侧为非int类型
  select 'abcdefg'::json ->> 'ab';
  select '''abcdefg'''::json ->> 2021-05-31;
  select '\"$$\"'::json ->>192.168.100.128/25;
  select '"["www@13^", 1, {"name": "john"}, "2"]"'::json ->> 1/2;