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From Yuzhao Chen <yuzhao....@gmail.com>
Subject Reorginize the SqlDialects ? Maybe just a discussion
Date Wed, 08 May 2019 02:52:36 GMT
Hi guys, recently there is a issue that want to integrate SqlDialect and SqlParser.Config
The background is that there are cases that we both use the SqlDialect and SqlParser.config,
but these config items are really a mess and come confused me a lot, so i list them there
and to see if we can make some progress.

### SqlDialect config items
- nullCollation: null values collation
- dataTypeSystem: type system to implement specific data types
- identifierQuoteString: starting quoting charactor
- identifierEndQuoteString: end quoting charactor
- DatabaseProduct: The name really confuse me ? Insn't it just a SqlDialect ?
- identifierEscapedQuote: escape quote for identifierQuoteString

### SqlParser.Config config items
- identifierMaxLength: max length of an identifier
- quotedCasing: casing of quoted identifier
- unquotedCasing: casing of unquoted identifier
- quoting: quoting charactor
- caseSensitive: if to parse the sql case sensitively
- parserFactory: a parser factory to profuce the parser
- SqlConformance: The name really confuse me ? Insn't it just a SqlDialect ?

### SqlConformance config items
- isLiberal: Whether this dialect supports features from a wide variety of dialects
- isGroupByAlias: group by column alias
- isGroupByOrdinal: group by column ordinal
- isHavingAlias: is having by column alias
- isSortByOrdinal: sort by column ordinal
- isSortByAlias: sort by column alias
- isSortByAliasObscures: Whether "empno" is invalid in "select empno as x from emp order by
empno"
- isFromRequired: Whether FROM clause is required in a SELECT statement
- isBangEqualAllowed: Whether the bang-equal token != is allowed as an alternative to <>
in the parser
- isPercentRemainderAllowed: Whether the "%" operator is allowed by the parser as an alternative
to the mod function
- isMinusAllowed: Whether MINUS is allowed as an alternative to EXCEPT in the parser
- isApplyAllowed()
- ...omitted

We can almost see the the SqlDialect mainly controls how we access other datasources(the runtime
config), the SqlParser.Config mainly controls the behavior of sql parsing(so we can mostly
see the keywords xxxAllowed).

Altough the 2 config class aims to different use cases, the both belong to the concept of
"SqlDialect", so i want to see if we can unify them, a SqlDialect config controls everything.
In CALCITE-3016 [2], we are planning to introduce SqlFlavor which still represent a "SqlDialect",
now we have SqlDialect/SqlConformance/DatabaseProduct/SqlFlavor, these classes really confused
me a lot.

So let's just have a discussion about how to re-orginize them or how we can do them berrer
:)

[1] https://issues.apache.org/jira/browse/CALCITE-3050
[2] https://issues.apache.org/jira/browse/CALCITE-3016


Best,
Danny Chan

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