SQL进阶:如何把字段中的键值对转为JSON格式?

一、问题描述

假如某张表的某列是键值对数据,如何把这个键值对转为json格式,数据如下所示

dynasty	value
唐朝	唐太宗:李世民;唐高宗:李治;唐玄宗:李隆基;…
汉朝	汉高祖:刘邦;汉文帝:刘恒;汉景帝:刘启;汉武帝:‘刘彻’;…

需要转成下面这种格式

dynasty	value
唐朝	[{“key”:“唐太宗”,“value”:“李世民”,“order”:“1”},{“key”:“唐高宗”,“value”:“李治”,“order”:“2”},{“key”:“唐玄宗”,“value”:“李隆基”,“order”:“3”}…]
汉朝	[{“key”:“汉高祖”,“value”:“刘邦”,“order”:“1”},{“key”:“汉文帝”,“value”:“刘恒”,“order”:“2”},{“key”:“汉景帝”,“value”:“刘启”,“order”:“3”},{“key”:“汉武帝”,“value”:“刘彻”,“order”:“2”}…]

二、ORACLE

<一>、键值对拆分(REGEXP_SUBSTR)

with split_data as (select dynasty,regexp_substr(value,'[^;]+',1,level) as part,level as part_numfrom tableconnect by regexp_substr(value,'[^;]+',1,level) is not null
)select dynasty,part_num,regexp_substr(part,'[^;]+',1,1) as key,regexp_substr(part,'[^;]+',1,2) as valuefrom split_data

执行完就是如下形式

dynasty	part_num	key	value
唐朝	1	唐太宗	李世民
唐朝	2	唐高宗	李治
唐朝	3	唐玄宗	李隆基
汉朝	1	汉高祖	刘邦
汉朝	2	汉文帝	刘恒
汉朝	3	汉景帝	刘启
汉朝	4	汉武帝	刘彻
…

<二>、转为JSON

转为JSON有现成的转JSON函数,完整代码如下

with split_data as (select dynasty,regexp_substr(value,'[^;]+',1,level) as part,level as part_numfrom tableconnect by regexp_substr(value,'[^;]+',1,level) is not null
),key_value_pairs as (select dynasty,part_num,regexp_substr(part,'[^;]+',1,1) as key,regexp_substr(part,'[^;]+',1,2) as valuefrom split_data
)select dynasty,json_arrayagg(josn_object('key' VALUE key,'value' VALUE value,'order' value split_num))from key_value_pairsgroup by dynasty

<三>、不足

• 有的键值对比较大,在ORACLE是CLOB类型,不支持字符串拆分,只能用如下MYSQL方法,再进行数据同步

三、MYSQL

<一>、键值对拆分(RECURSIVE)

• MYSQL中没有正则字符串拆分函数,只能用递归进行拆分

with recursive kv_split as (select dynasty,trim(substring_index(value,';',1)) as kv_pairs,trim(substring(value,char_length(substring_index(value,';',1)) + 2)) as remaining,1 as splt_numfrom tableunion allselect dynasty,trim(substring_index(remaining,';',1)) as kv_pairs,trim(substring(remaining,char_length(substring_index(value,';',1)) + 2)) as remaining,split_num + 1 as splt_numfrom kv_splitwhere remaining != ''
)select dynasty,kv_pairs,splt_num from kv_split

执行完为如下形式,跟ORACLE大同小异

dynasty	part_num	kv_pairs
唐朝	1	唐太宗:李世民
唐朝	2	唐高宗:李治
唐朝	3	唐玄宗:李隆基
汉朝	1	汉高祖:刘邦
汉朝	2	汉文帝:刘恒
汉朝	3	汉景帝:刘启
汉朝	4	汉武帝:刘彻
…

<二>、转为JSON

转成JSON跟ORACLE一样,有现成的转JSON函数,完整代码如下所示

with recursive kv_split as (select dynasty,trim(substring_index(value,';',1)) as kv_pairs,trim(substring(value,char_length(substring_index(value,';',1)) + 2)) as remaining,1 as splt_numfrom tableunion allselect dynasty,trim(substring_index(remaining,';',1)) as kv_pairs,trim(substring(remaining,char_length(substring_index(value,';',1)) + 2)) as remaining,split_num + 1 as splt_numfrom kv_splitwhere remaining != ''
)select dynasty,json_arrayagg(json_object('key',cast(substring_index(kv_pairs,':',1) as unsigned),'value',substring_index(kv_pairs,':',-1),'order',split_num)) as json_resultfrom kv_splitgroup by dynasty