*: add builtin aggregate function VAR_POP

[githubFZX]

What problem does this PR solve?

#7623

What is changed and how it works?

Implement builtin aggregate function 'varpop' in tidb and use the algorithm described by Chan, Golub, and LeVeque in "Algorithms for computing the sample variance: analysis and recommendations" to calculate the variance.

Check List

Tests

• Unit test

---

mysql> create table numerical_t(
    -> a tinyint,
    -> b smallint,
    -> c mediumint,
    -> d int,
    -> e bigint,
    -> f float,
    -> g double,
    -> h decimal
    -> );
Query OK, 0 rows affected (0.10 sec)

---

mysql> insert into numerical_t 
    -> values
    -> (1, 2, 3, 4, 5, 6.1, 7.2, 8.3), 
    -> (2, 3, 4, 5, 6, 7.2, 8.3, 9.4),
    -> (1, 3, 4, 5, 6, 7.1, 8.2, 9.3);
Query OK, 3 rows affected, 3 warnings (0.01 sec)

---

mysql> select a, var_pop(b),var_pop(c),var_pop(d),var_pop(e),var_pop(f),var_pop(g),var_pop(h) from numerical_t group by a;
+------+------------+------------+------------+------------+------------+------------+------------+
| a    | var_pop(b) | var_pop(c) | var_pop(d) | var_pop(e) | var_pop(f) | var_pop(g) | var_pop(h) |
+------+------------+------------+------------+------------+------------+------------+------------+
|    2 |          0 |          0 |          0 |          0 |          0 |          0 |          0 |
|    1 |       0.25 |       0.25 |       0.25 |       0.25 |       0.25 |       0.25 |       0.25 |
+------+------------+------------+------------+------------+------------+------------+------------+
2 rows in set (0.01 sec)

[claassistantio]

All committers have signed the CLA.

[zz-jason]

Hi @githubFZX, gofmt check failed:

[2019-12-18T02:11:57.303Z] gofmt (simplify)
[2019-12-18T02:12:03.845Z] executor/aggfuncs/func_varpop.go
[2019-12-18T02:12:03.845Z] make: *** [fmt] Error 1

You can run make check on your local machine to fix this

[githubFZX]

Why does the above error occur in unit test？I just modify go.mod to update parser. I need help.

[wshwsh12]

LGTM. But I want to know why update tipb, atomic, zap, tools in go.mod ? Only parser is not enough?

[githubFZX]

LGTM. But I want to know why update tipb, atomic, zap, tools in go.mod ? Only parser is not enough?

I used command ”GO111MODULE=on go get -u github.com/pingcap/parser@master“ to update parser. But the others changed together.

[zz-jason]

LGTM. But I want to know why update tipb, atomic, zap, tools in go.mod ? Only parser is not enough?

I used command ”GO111MODULE=on go get -u github.com/pingcap/parser@master“ to update parser. But the others changed together.

@githubFZX @wshwsh12 you can run make tidy to clean the unnecessary modifications on go.mod and go.sum

[githubFZX]

LGTM. But I want to know why update tipb, atomic, zap, tools in go.mod ? Only parser is not enough?

I used command ”GO111MODULE=on go get -u github.com/pingcap/parser@master“ to update parser. But the others changed together.

@githubFZX @wshwsh12 you can run make tidy to clean the unnecessary modifications on go.mod and go.sum

Ok, thank you!

[zz-jason]

@githubFZX any update? BTW, this PR is conflicted with the master branch, please use make tidy to clean go.mod/go.sum and resolve the conflicts in your spare time.

[githubFZX]

@githubFZX any update? BTW, this PR is conflicted with the master branch, please use make tidy to clean go.mod/go.sum and resolve the conflicts in your spare time.

Ok, i will fix it later.

[wshwsh12]

@githubFZX It seems that someone has updated parser in other pr. Now we can reset the go.mod and go.sum to master and merge this pr .

[zz-jason]

LGTM

[sre-bot]

Your auto merge job has been accepted, waiting for 14361

[zz-jason]

/run-all-tests

[sre-bot]

/run-all-tests

[sre-bot]

@githubFZX merge failed.

[githubFZX]

There is no error when I use commands "make test" and "make dev" in my local machine. What should I do to resolve this problem that unit-test can not pass?