executor: support the remained types for max/min

[XuHuaiyu]

What have you changed? (mandatory)

support String/ Time/ Duration/ JSON for max/min

What is the type of the changes? (mandatory)

• Improvement

How has this PR been tested? (mandatory)

The existing test cases.
randgen-test

Does this PR affect documentation (docs/docs-cn) update? (mandatory)

no

Does this PR affect tidb-ansible update? (mandatory)

no

Does this PR need to be added to the release notes? (mandatory)

no

Refer to a related PR or issue link (optional)

#6952

Benchmark result if necessary (optional)

Add a few positive/negative examples (optional)

[zz-jason]

LGTM

[zz-jason]

/run-all-tests

[zz-jason]

@XuHuaiyu please add some labels

[crazycs520]

LGTM

[XuHuaiyu]

/run-common-test tidb-test=pr/578
/run-integration-common-test tidb-test=pr/578

[XuHuaiyu]

/run-common-test tidb-test=pr/578
/run-integration-common-test tidb-test=pr/578

[XuHuaiyu]

I tried these ways @zz-jason

func BenchmarkCopyString(b *testing.B) {
	a := "123"
	for i := 0; i < b.N; i ++{
		a = fmt.Sprintf("%s", a)
	}
}

func BenchmarkCopyString2(b *testing.B) {
	a := "123"
	for i := 0; i < b.N; i ++{
		a = a + ""
	}
}

func BenchmarkCopyString3(b *testing.B) {
	a := "123"
	for i := 0; i < b.N; i ++{
		bytes := []byte(a)
		b := make([]byte, len(bytes))
		copy(b,bytes )
		a = string(b)
	}
}

func BenchmarkCopyString4(b *testing.B) {
	a := "123"
	for i := 0; i < b.N; i ++{
		pbytes := (*reflect.SliceHeader)(unsafe.Pointer(&b))
		b := make([]byte, pbytes.Len)
		copy(b, a)
		a = string(b)
	}
}

BenchmarkCopyString-4 10000000 132 ns/op 19 B/op 2 allocs/op
BenchmarkCopyString2-4 100000000 11.4 ns/op 0 B/op 0 allocs/op
BenchmarkCopyString3-4 30000000 45.6 ns/op 6 B/op 2 allocs/op
BenchmarkCopyString4-4 200 10791498 ns/op 52690966 B/op 2 allocs/op

[zz-jason]

@XuHuaiyu BenchmarkCopyString4 is not correct, should not use b directly

[zz-jason]

/run-all-tests tidb-test=pr/578

[crazycs520]

@XuHuaiyu BenchmarkCopyString2 is not correct, it have not copy

import . "github.com/pingcap/tidb/util/hack"
func TestStringcs(t *testing.T) {
	a := "abc"
	b := a + ""
	bufA := Slice(a)
	bufB := Slice(b)
	fmt.Println(&bufA[0], &bufB[0]) // the adress is same
}

Another question: Why we need to copy string? string cannot be modified after create.

Still need discussing

[crazycs520]

Why only change this line? line#363,411?

[XuHuaiyu]

caused by the implementation of different compare function.

[winoros]

Better wrap it as a method in util package.

CI failed

[zz-jason]

How about s/CopyString/Copy/? We usually call the function with the package name, "stringutil.Copy()" would be simpler.

[crazycs520]

add comment why we need to copy a string. because the string is hack from byte(chunk)

[zz-jason]

no need to add it here, should add the comments in the caller side.

[zz-jason]

/run-all-tests tidb-test=pr/578