codec, json: fix type json hash group key

[zxh326]

What problem does this PR solve?

Issue Number: close #10467

What is changed and how it works?

What's Changed:
change hashgroupkey when col type is json

How it Works:
change int64 in json to float64

I write a samle code to test benchmark gist，will lose some performance in aggregate executor when col type is json

goos: darwin
goarch: amd64
pkg: leet-go/jsont
BenchmarkHashJsonValue-8        12260102                96.3 ns/op            80 B/op          2 allocs/op
BenchmarkBasic-8                32172847                36.5 ns/op            48 B/op          1 allocs/op
PASS
ok      leet-go/jsont   3.095s

Related changes

• Need to cherry-pick to the release branch

Check List

Tests

• Unit test
• Integration test

Side effects
N/A

Release note

[wshwsh12]

Sorry for the late reply, and thanks for your contribution.
I think converting int64 to float64 is not a good idea. It will convert different int64 to the same float64. For example, (run in this pr.)

tidb> create table tx2 (col json);
Query OK, 0 rows affected (0.00 sec)

tidb> insert into tx2 values (json_array(922337203685477580));
Query OK, 1 row affected (0.01 sec)

tidb> insert into tx2 values (json_array(922337203685477581));
Query OK, 1 row affected (0.00 sec)

tidb> select col, count(1) from tx2 group by col;
+----------------------+----------+
| col                  | count(1) |
+----------------------+----------+
| [922337203685477580] |        2 |
+----------------------+----------+
1 row in set (0.00 sec)

[zxh326]

Sorry for the late reply, and thanks for your contribution.
I think converting int64 to float64 is not a good idea. It will convert different int64 to the same float64. For example, (run in this pr.)

tidb> create table tx2 (col json);
Query OK, 0 rows affected (0.00 sec)

tidb> insert into tx2 values (json_array(922337203685477580));
Query OK, 1 row affected (0.01 sec)

tidb> insert into tx2 values (json_array(922337203685477581));
Query OK, 1 row affected (0.00 sec)

tidb> select col, count(1) from tx2 group by col;
+----------------------+----------+
| col                  | count(1) |
+----------------------+----------+
| [922337203685477580] |        2 |
+----------------------+----------+
1 row in set (0.00 sec)

I found a similar bug in #16267

[wjhuang2016]

Friendly ping @zxh326, could you update this PR?

[sre-bot]

No release note, Please follow https://github.com/pingcap/community/blob/master/contributors/release-note-checker.md

[zz-jason]

these are all the type codes:

 27 const (
 28     // TypeCodeObject indicates the JSON is an object.
 29     TypeCodeObject TypeCode = 0x01
 30     // TypeCodeArray indicates the JSON is an array.
 31     TypeCodeArray TypeCode = 0x03
 32     // TypeCodeLiteral indicates the JSON is a literal.
 33      const TypeCodeInt64 byte = 9
 34      TypeCodeInt64 indicates the JSON is a signed integer. .
 35     TypeCodeInt64 TypeCode = 0x09
 36     // TypeCodeUint64 indicates the JSON is a unsigned integer.
 37     TypeCodeUint64 TypeCode = 0x0a
 38     // TypeCodeFloat64 indicates the JSON is a double float number.
 39     TypeCodeFloat64 TypeCode = 0x0b
 40     // TypeCodeString indicates the JSON is a string.
 41     TypeCodeString TypeCode = 0x0c
 42 )

For simplicity, you can just append the value of int64 to buf instead of converting it to float64.

[zxh326]

ok, thx, I'll try that in the near future.

[ti-srebot]

@zxh326,Thanks for your review. The bot only counts LGTMs from Reviewers and higher roles, but you're still welcome to leave your comments.You are not a reviewer or committer or co-leader or leader.

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[ti-srebot]

@zxh326, please update your pull request.

[ti-srebot]

@zxh326, please update your pull request.

[ti-srebot]

@zxh326 PR closed due to no update for a long time. Feel free to reopen it anytime.