parser: implement Restore for SelectStmt

[AndrewDi]

implement Restore for SelectStmt
implement Restore for UnionSelectList
implement Restore for SubqueryExpr
implement Restore for CompareSubqueryExpr
implement Restore for TableOptimizerHint

Add SelectStmt test case, the rest would be add soon, too many test case.

Issue: pingcap/tidb#8532

[kennytm]

Thanks for the contribution! As TableOptimizerHint is already handled by @exialin in #151, could one of you back out the change?

[AndrewDi]

@kennytm You can free to choose one, I implement it only because SelectStmt contains it.

[exialin]

@AndrewDi Since you've resolved the problem, it is better to include TableOptimizerHint in this PR. #151 can be closed later.

[AndrewDi]

@kennytm @leoppro Almost all the SELECT statement test case I have found in Parser_test has been added, But it still have one restore problem here:

parser/parser_test.go

Lines 1430 to 1447 in d8e164f

	{`select .78+123`, true, ""},
	{`select .78+.21`, true, ""},
	{`select .78-123`, true, ""},
	{`select .78-.21`, true, ""},
	{`select .78--123`, true, ""},
	{`select .78*123`, true, ""},
	{`select .78*.21`, true, ""},
	{`select .78/123`, true, ""},
	{`select .78/.21`, true, ""},
	{`select .78,123`, true, ""},
	{`select .78,.21`, true, ""},
	{`select .78 , 123`, true, ""},
	{`select .78.123`, false, ""},
	{`select .78#123`, true, ""}, // select .78
	{`insert float_test values(.67, 'string');`, true, ""},
	{`select .78'123'`, true, ""}, // select .78 as '123'
	{"select .78`123`", true, ""}, // select .78 as `123`
	{`select .78"123"`, true, ""}, // select .78 as "123"

If we restore a statement like SELECT .78, output would become SELECT 0.78, so the MyDeciaml's digitsInt will change from 0 to 1, DeepEquals will fail.

Besides SELECT WITH Exists Clause test case should add after #126 merged.

[zier-one]

@kennytm @leoppro Almost all the SELECT statement test case I have found in Parser_test has been added, But it still have one restore problem here:
parser/parser_test.go

Lines 1430 to 1447 in d8e164f

{select .78+123, true, ""},
{select .78+.21, true, ""},
{select .78-123, true, ""},
{select .78-.21, true, ""},
{select .78--123, true, ""},
{select .78*123, true, ""},
{select .78*.21, true, ""},
{select .78/123, true, ""},
{select .78/.21, true, ""},
{select .78,123, true, ""},
{select .78,.21, true, ""},
{select .78 , 123, true, ""},
{select .78.123, false, ""},
{select .78#123, true, ""}, // select .78
{insert float_test values(.67, 'string');, true, ""},
{select .78'123', true, ""}, // select .78 as '123'
{"select .78123", true, ""}, // select .78 as 123
{select .78"123", true, ""}, // select .78 as "123"

If we restore a statement like SELECT .78, output would become SELECT 0.78, so the MyDeciaml's digitsInt will change from 0 to 1, DeepEquals will fail.
Besides SELECT WITH Exists Clause test case should add after #126 merged.

could you handle this by updating CleanNodeText

[AndrewDi]

this attr could not update now ...

[AndrewDi]

@leoppro PTAL, use another way to deal with Decimal type.

[zier-one]

LGTM

[zier-one]

@kennytm PTAL

[AndrewDi]

@kennytm Comment handled

[kennytm]

Lgtm