evaluator,parser: support ASCII()

[zyguan]

Hi, I'm reading the source code and willing to help to implement some basic builtin functions. However, I'm not sure if I did things right. Please correct me if I made mistake.

[CLAassistant]

All committers have accepted the CLA.

[shenli]

@zyguan Thanks for your PR. Please sign the CLA.

[zyguan]

@shenli Sorry, I forgot it.

[shenli]

ASCII is not a reserved keyword. It should not be here. You can put it into UnReservedKeyword rule: https://github.com/pingcap/tidb/blob/master/parser/parser.y#L1819

See: https://dev.mysql.com/doc/refman/5.7/en/keywords.html

[zyguan]

Ok, I put it there because of sql_yacc.yy. I'll fix it later.

[zyguan]

@shenli I see COALESCE is a nonreserved keyword according to https://dev.mysql.com/doc/refman/5.7/en/keywords.html. However, it appears in NotKeywordToken in https://github.com/pingcap/tidb/blob/master/parser/parser.y. I'm a little confused.

[shenli]

@zyguan I think it is a mistake. Good catch!

[shenli]

LGTM
@coocood PTAL

[coocood]

LGTM
Thank you!

[shenli]

@zyguan Thanks for your contribution! May I have your email address?

[zyguan]

@shenli Sure! [email protected]

[ngaut]

Thank you, This branch is out-of-date, Could you merge or rebase master ? @zyguan

[zyguan]

@ngaut Yes, Of course! Wait a minute.

[ngaut]

Thanks @zyguan