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MDEV-38873 json_extract returns NULL through derived table #4680

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MDEV-38873 json_extract returns NULL through derived table #4680

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12 changes: 12 additions & 0 deletions mysql-test/main/func_json.result
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Original file line number Diff line number Diff line change
Expand Up @@ -5764,4 +5764,16 @@ NULL NULL NULL NULL NULL NULL NULL NULL
{"key": "value", "key2": "value2"} 1 0 0 1 0 1 1
{"key": "value", "key": "value2"} 1 0 0 1 0 0 1
DROP TABLE test_default_json;
SELECT json_extract(t.j, '$')
FROM (SELECT json_extract('["a",1]', '$') AS j) AS t;
json_extract(t.j, '$')
["a", 1]
SELECT json_extract(t.j, '$[0]')
FROM (SELECT json_extract('["a",1]', '$') AS j) AS t;
json_extract(t.j, '$[0]')
"a"
SELECT json_extract(t.j, '$')
FROM (SELECT json_extract('{"key":"value"}', '$') AS j) AS t;
json_extract(t.j, '$')
{"key": "value"}
# End of 12.3
9 changes: 9 additions & 0 deletions mysql-test/main/func_json.test
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Expand Up @@ -4489,4 +4489,13 @@ FROM test_default_json;

DROP TABLE test_default_json;

SELECT json_extract(t.j, '$')
FROM (SELECT json_extract('["a",1]', '$') AS j) AS t;

SELECT json_extract(t.j, '$[0]')
FROM (SELECT json_extract('["a",1]', '$') AS j) AS t;

SELECT json_extract(t.j, '$')
FROM (SELECT json_extract('{"key":"value"}', '$') AS j) AS t;

--echo # End of 12.3
7 changes: 6 additions & 1 deletion sql/item_jsonfunc.cc
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Expand Up @@ -1139,7 +1139,12 @@ bool Item_json_str_multipath::fix_length_and_dec(THD *thd)
bool Item_func_json_extract::fix_length_and_dec(THD *thd)
{
collation.set(args[0]->collation);
max_length= args[0]->max_length * (arg_count - 1);
/*
json_extract() passes its result through json_nice() with LOOSE format,
which can expand the output (e.g. adding spaces after commas and colons).
Multiply by 2 to account for this, matching JSON_FORMAT(LOOSE) behavior.
*/
max_length= args[0]->max_length * (arg_count - 1) * 2;

mark_constant_paths(paths, args+1, arg_count-1);
set_maybe_null();
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