问题
I have a table, Table1 that contains a XML data type column, ColumnA and another JSONB column ColumnB
How do I convert the data from ColumnA into ColumnB, presumably using an SQL UPDATE statement. Is there a built-in function in Postgres that does this?
回答1:
There is no out-of-box functions as I know.
Try:
create or replace function xml_to_json(p_xml xml) returns jsonb as $$
declare
result json;
root text;
childs jsonb;
attr jsonb;
txt text;
begin
-- Get root element name
select (xpath('name(/*)', p_xml))[1]::text into root;
-- Process child nodes
select json_agg(xml_to_json(z))
from unnest(xpath('/'||root||'/*', p_xml)) with ordinality as c(z,i)
into childs;
-- Read attributes
select jsonb_agg(jsonb_build_object((xpath('name(/'||root||'/@*['||i||'])', p_xml))[1]::text, v))
from unnest(xpath('/'||root||'/@*', p_xml)::text[]) with ordinality as a(v,i)
into attr;
-- Read text
select (xpath('/'||root||'/text()', p_xml))[1]::text into txt;
-- Build object
result := jsonb_build_object(root, jsonb_build_object('attr', attr, 'text', txt, 'childs', childs));
return result;
end $$ language plpgsql immutable;
Test:
with t(x) as (values
('<root bar="foo" name="test" foo="bar">
<aaa bbb="111">
foo
bar
</aaa>
<bbb>
<ccc>222</ccc>
</bbb>
</root>'::xml),
('<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
<book>
<title lang="en">Harry Potter</title>
<price>29.99</price>
</book>
<book>
<title lang="en">Learning XML</title>
<price>39.95</price>
</book>
</bookstore>'))
select jsonb_pretty(xml_to_json(x)) from t;
And output:
jsonb_pretty
---------------------------------------------------------
{ +
"root": { +
"attr": [ +
{ +
"bar": "foo" +
}, +
{ +
"name": "test" +
}, +
{ +
"foo": "bar" +
} +
], +
"text": "\n ", +
"childs": [ +
{ +
"aaa": { +
"attr": [ +
{ +
"bbb": "111" +
} +
], +
"text": "\n foo\n bar\n ", +
"childs": null +
} +
}, +
{ +
"bbb": { +
"attr": null, +
"text": "\n ", +
"childs": [ +
{ +
"ccc": { +
"attr": null, +
"text": "222", +
"childs": null +
} +
} +
] +
} +
} +
] +
} +
}
{ +
"bookstore": { +
"attr": null, +
"text": "\n ", +
"childs": [ +
{ +
"book": { +
"attr": null, +
"text": "\n ", +
"childs": [ +
{ +
"title": { +
"attr": [ +
{ +
"lang": "en" +
} +
], +
"text": "Harry Potter",+
"childs": null +
} +
}, +
{ +
"price": { +
"attr": null, +
"text": "29.99", +
"childs": null +
} +
} +
] +
} +
}, +
{ +
"book": { +
"attr": null, +
"text": "\n ", +
"childs": [ +
{ +
"title": { +
"attr": [ +
{ +
"lang": "en" +
} +
], +
"text": "Learning XML",+
"childs": null +
} +
}, +
{ +
"price": { +
"attr": null, +
"text": "39.95", +
"childs": null +
} +
} +
] +
} +
} +
] +
} +
}
(2 rows)
来源：https://stackoverflow.com/questions/38142623/how-to-convert-a-xml-into-jsonb-within-postgres