How to use mysql5.6 to parse JSON strings
mysql5.6 解析JSON字符串
支持复杂的嵌套格式
废话不多说，先上代码。
CREATE FUNCTION `json_parse`(`jsondata` longtext,`keyname` text) RETURNS text CHARSET utf8
BEGIN
DECLARE delim VARCHAR(128);
DECLARE result longtext;
DECLARE startpos INTEGER;
DECLARE endpos INTEGER;
DECLARE endpos1 INTEGER;
DECLARE findpos INTEGER;
DECLARE leftbrace INTEGER;
DECLARE tmp longtext;
DECLARE tmp2 longtext;
DECLARE Flag INTEGER;
SET delim = CONCAT('"', keyname, '": "');
SET startpos = locate(delim,jsondata);
IF startpos > 0 THEN
SET findpos = startpos+length(delim);
SET leftbrace = 1;
SET endpos = 0;
SET Flag =1;
get_token_loop: repeat
IF substr(jsondata,findpos,2)='\\"' THEN
SET findpos = findpos + 2;
iterate get_token_loop;
ELSEIF substr(jsondata,findpos,2)='\\\\' THEN
SET findpos = findpos + 2;
iterate get_token_loop;
ELSEIF substr(jsondata,findpos,1)='"' AND Flag = 1 THEN
SET endpos = findpos;
SET findpos = LENGTH(jsondata)+1;
leave get_token_loop;
END IF;
SET findpos = findpos + 1;
UNTIL findpos > LENGTH(jsondata) END repeat;
IF endpos > 0 THEN
SELECT
substr(
jsondata
,startpos
+length(delim)#取出value值的起始位置
,endpos#取出value值的结束位置
-(
startpos
+length(delim)
)#减去value值的起始位置，得到value值字符长度
) INTO result
FROM DUAL;
SET result= replace(result,'\\"','"');
SET result= replace(result,'\\\\','\\');
ELSE
SET result=null;
END IF;
/*
SELECT
substr(
jsondata
,locate(delim,jsondata)
+length(delim)#取出value值的起始位置
,locate(
'"'
,jsondata
,locate(delim,jsondata)
+length(delim)
)#取出value值的结束位置
-(
locate(delim,jsondata)
+length(delim)
)#减去value值的起始位置，得到value值字符长度
) INTO result
FROM DUAL; */
ELSE
SET delim = CONCAT('"', keyname, '": {');
SET startpos = locate(delim,jsondata);
IF startpos > 0 THEN
SET findpos = startpos+length(delim);
SET leftbrace = 0;
SET endpos = 0;
SET Flag =0;
get_token_loop: repeat
IF substr(jsondata,findpos,2)='{"' THEN
SET leftbrace = leftbrace + 1;
SET findpos = findpos + 2;
iterate get_token_loop;
ELSEIF substr(jsondata,findpos,2)='\\"' THEN
SET findpos = findpos + 2;
iterate get_token_loop;
ELSEIF substr(jsondata,findpos,3)=': "' THEN
SET Flag = 1;
SET findpos = findpos + 3;
iterate get_token_loop;
ELSEIF substr(jsondata,findpos,1)='"' THEN
SET Flag = 0;
ELSEIF substr(jsondata,findpos,1)='}' AND Flag = 0 THEN
IF leftbrace > 0 THEN
SET leftbrace = leftbrace - 1;
ELSE
SET endpos = findpos;
SET findpos = LENGTH(jsondata)+1;
END IF;
END IF;
SET findpos = findpos + 1;
UNTIL findpos > LENGTH(jsondata) END repeat;
IF endpos > 0 THEN
SELECT
substr(
jsondata
,startpos
+length(delim)#取出value值的起始位置
,endpos#取出value值的结束位置
-(
startpos
+length(delim)
)#减去value值的起始位置，得到value值字符长度
) INTO result
FROM DUAL;
SET result=CONCAT("{",result, '}');
ELSE
SET result=null;
END IF;
ELSE
SET delim = CONCAT('"', keyname, '": [');
SET startpos = locate(delim,jsondata);
IF startpos > 0 THEN
SET findpos = startpos+length(delim);
SET leftbrace = 0;
SET endpos = 0;
SET tmp = substring_index(jsondata,delim,-1);
SET tmp2 = substring_index(tmp,']',1);
IF locate('[',tmp2) =0 THEN
SET endpos = locate(']',tmp);
SET endpos = endpos+findpos-1;
ELSE
get_token_loop: repeat
IF substr(jsondata,findpos,2)='\\"' THEN
SET findpos = findpos + 2;
iterate get_token_loop;
ELSEIF substr(jsondata,findpos,3)=': "' THEN
SET Flag = 1;
SET findpos = findpos + 3;
iterate get_token_loop;
ELSEIF substr(jsondata,findpos,1)='[' AND Flag = 0 THEN
SET leftbrace = leftbrace + 1;
SET findpos = findpos + 1;
iterate get_token_loop;
ELSEIF substr(jsondata,findpos,1)='"' THEN
SET Flag = 0;
ELSEIF substr(jsondata,findpos,1)=']' AND Flag = 0 THEN
IF leftbrace > 0 THEN
SET leftbrace = leftbrace - 1;
ELSE
SET endpos = findpos;
SET findpos = LENGTH(jsondata)+1;
END IF;
END IF;
SET findpos = findpos + 1;
UNTIL findpos > LENGTH(jsondata) END repeat;
END IF;
IF endpos > 0 THEN
SELECT
substr(
jsondata
,startpos
+length(delim)#取出value值的起始位置
,endpos#取出value值的结束位置
-(
locate(delim,jsondata)
+length(delim)
)#减去value值的起始位置，得到value值字符长度
) INTO result
FROM DUAL;
SET result=CONCAT("[",result, ']');
ELSE
SET result=null;
END IF;
ELSE
SET delim = CONCAT('"', keyname, '": ');
SET startpos = locate(delim,jsondata);
IF startpos > 0 THEN
SET endpos = locate(',',jsondata,startpos+length(delim));
SET endpos1 = locate('}',jsondata,startpos+length(delim));
IF endpos>0 OR endpos1>0 THEN
IF endpos1>0 AND endpos1 < endpos OR endpos =0 THEN
SET endpos = endpos1;
END IF;
SELECT
substr(
jsondata
,startpos
+length(delim)#取出value值的起始位置
,endpos#取出value值的结束位置
-(
locate(delim,jsondata)
+length(delim)
)#减去value值的起始位置，得到value值字符长度
) INTO result
FROM DUAL;
IF STRCMP(result,'null')=0 THEN
SET result=null;
END IF;
ELSE
SET result=null;
END IF;
ELSE
SET result=null;
END IF;
END IF;
END IF;
END IF;
if result='' and RIGHT(keyname,2)='Id' then
SET result=null;
end if;
RETURN result;
ENDjsondata需要严格的json格式（注意逗号和分号以及双引号之间的空格）
SET jsondata='{"CurrentPage": 1, "data": [{"config": "123"}, {"config": "456"}], "PageSize": 10}'
SELECT json_parse(jsondata, 'CurrentPage') INTO CurrentPage;
SELECT json_parse(jsondata, 'data') INTO data;这边如果想获取config的内容，可以这样处理
SET count = (LENGTH(data)-LENGTH(REPLACE(data,'},','')))/2+1;
SET i = 0;
WHILE i < count DO
SET SetObject = SUBSTRING_INDEX(SUBSTRING_INDEX(data,'},',i+1),'},',-1);
IF LENGTH(SetObject)>0 THEN
SELECT json_parse(SetObject, 'config') INTO config;
END IF;
SET i = i + 1;
END WHILE;不足之处，jsondata数据多的情况下，会有效率问题。
mysql5.6及以下解析json方法
之前在公司发现在线的查询平台是MySQL5.6，不能用JSON_EXTRACT，也不能用存储过程，所以只能自己编了一个简单的小查询，几条数据还是能查的，如果数据量大的话，估计耗的资源就会比较多。
先说一下问题的背景
是想在'{"platform":"Android","source":"tt","details":null}'这一串东西里面找到source这个key对应的value值。
这个方法是先找到source":"这个字符串的起始位置和长度，这样就能够找到value值的起始位置；再找到这个字符串以后第一个"出现的位置，就能得到value值的结束位置。
再利用substr函数，就可以取出对应的位置。
下面是对应的代码
SELECT
'{"platform":"Android","source":"tt","details":null}' as 'sample'
,substr(
'{"platform":"Android","source":"tt","details":null}'
,locate('source":"','{"platform":"Android","source":"tt","details":null}')
+length('source":"')#取出value值的起始位置
,locate(
'"'
,'{"platform":"Android","source":"tt","details":null}'
,locate('source":"','{"platform":"Android","source":"tt","details":null}')
+length('source":"')
)#取出value值的结束位置
-(
locate('source":"','{"platform":"Android","source":"tt","details":null}')
+length('source":"')
)#减去value值的起始位置，得到value值字符长度
) as result
FROM DUAL运行以后，就得到result的结果，就是tt。如果需要其他元素，就替换一下对应的key值和字段，就好了。
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