expression, planner: fix decimal results for aggregate functions (#20017)

[ti-srebot]

cherry-pick #20017 to release-4.0

---

What problem does this PR solve?

Issue Number: close #19426, fix PR #19592

Problem Summary:

Execute

create table t(a int primary key, b int);
insert into t values (1, 11), (4, 44), (2, 22), (3, 33);

Obtained

mysql> select sum(case when a <= 0 or a > 1000 then 0.0 else b end) from t;
+-------------------------------------------------------+
| sum(case when a <= 0 or a > 1000 then 0.0 else b end) |
+-------------------------------------------------------+
|                                                   110 |
+-------------------------------------------------------+
1 row in set (0.01 sec)

mysql> select group_concat(case when a <= 0 or a > 1000 then 0.0 else b end) from t;
+----------------------------------------------------------------+
| group_concat(case when a <= 0 or a > 1000 then 0.0 else b end) |
+----------------------------------------------------------------+
| 11,22,33,44                                                    |
+----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select distinct case when a <= 0 or a > 1000 then 0.0 else b end from t;
+--------------------------------------------------+
| case when a <= 0 or a > 1000 then 0.0 else b end |
+--------------------------------------------------+
|                                               11 |
|                                               22 |
|                                               33 |
|                                               44 |
+--------------------------------------------------+
4 rows in set (0.00 sec)

Expect

mysql> select sum(case when a <= 0 or a > 1000 then 0.0 else b end) from t;
+-------------------------------------------------------+
| sum(case when a <= 0 or a > 1000 then 0.0 else b end) |
+-------------------------------------------------------+
|                                                 110.0 |
+-------------------------------------------------------+
1 row in set (0.00 sec)

mysql>  select group_concat(case when a <= 0 or a > 1000 then 0.0 else b end) from t;
+----------------------------------------------------------------+
| group_concat(case when a <= 0 or a > 1000 then 0.0 else b end) |
+----------------------------------------------------------------+
| 11.0,22.0,33.0,44.0                                            |
+----------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select distinct case when a <= 0 or a > 1000 then 0.0 else b end from t;
+--------------------------------------------------+
| case when a <= 0 or a > 1000 then 0.0 else b end |
+--------------------------------------------------+
|                                             11.0 |
|                                             22.0 |
|                                             33.0 |
|                                             44.0 |
+--------------------------------------------------+
4 rows in set (0.00 sec)

What is changed and how it works?

• wrap cast as decimal for arguments of group_concat to preserve fraction part digits of the results.
• round the decimal final result in AppendFinalResult2Chunk to the argument's precision.

Related changes

• Need to cherry-pick to the release branch 3.0, 4.0

Check List

Tests

• Unit test
• Integration test

Side effects

• Performance regression
  • Consumes more CPU
  • Consumes more MEM

Release note

• fix the fraction part of decimal results for aggregate functions

[ti-srebot]

/run-all-tests

[winoros]

lgtm

[qw4990]

LGTM

[qw4990]

/merge

[ti-srebot]

/run-all-tests

[ti-srebot]

@ti-srebot merge failed.

[dyzsr]

/run-common-test tidb-test=pr/1100
/run-integration-common-test tidb-test=pr/1100

[dyzsr]

/run-common-test
/run-integration-common-test

[dyzsr]

/run-common-test tidb-test=pr/1104
/run-integration-common-test tidb-test=pr/1104

[dyzsr]

Need to merge https://github.com/pingcap/tidb-test/pull/1104 first.

[lzmhhh123]

/merge

[ti-srebot]

Sorry @lzmhhh123, you don't have permission to trigger auto merge event on this branch.

[qw4990]

/merge

[ti-srebot]

Sorry @qw4990, you don't have permission to trigger auto merge event on this branch.

[qw4990]

/run-all-tests

[dyzsr]

/run-common-test tidb-test=pr/1104
/run-integration-common-test tidb-test=pr/1104

[dyzsr]

/run-common-test tidb-test=pr/1104
/run-integration-common-test tidb-test=pr/1104

[dyzsr]

/run-integration-common-test tidb-test=pr/1104

[jebter]

/merge

[ti-srebot]

/run-all-tests

[ti-srebot]

@ti-srebot merge failed.

[jebter]

/run-common-test

[jebter]

/run-integration-common-test

[jebter]

/merge

[ti-srebot]

/run-all-tests

[ti-srebot]

@ti-srebot merge failed.

[jebter]

/merge

[ti-srebot]

Your auto merge job has been accepted, waiting for:

• 21336

[ti-srebot]

/run-all-tests

[ti-srebot]

@ti-srebot merge failed.

[jebter]

/run-unit-test