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Posted to notifications@shardingsphere.apache.org by GitBox <gi...@apache.org> on 2021/08/12 10:33:23 UTC
[GitHub] [shardingsphere] RaigorJiang opened a new issue #11784: [DISCUSS] design a grammar for `Preview SQL`
RaigorJiang opened a new issue #11784:
URL: https://github.com/apache/shardingsphere/issues/11784
Hi community,
I am designing `Preview SQL` syntax for DistSQL, which has the following characteristics:
1. `Preview` is a keyword, `SQL` can be any statement, such as SELECT, CREATE, DROP, etc.;
2. There is at least one blank character between the `Preview` keyword and the `SQL` statement;
3. It is expected that after ANTLR parses the input text, it will recognize `SQL` as a `String object`;
### Here is an example:
input text:
```sql
preview select * from t_order;
```
parse result:
### There are some difficulties:
1. We need a lexer grammar that can match any input sentence after the keyword, which did not exist before;
2. In the existing ANTLR grammar file, we define the following lexer grammar to ignore whitespace characters
```antlr
WS
: [ \t\r\n] + ->skip
;
```
But the `Preview` statement needs to recognize blank characters to distinguish between the keyword and the statement after it;
3. If the lexer grammar not ignoring spaces is declared in the existing grammar, it will cause the original grammar parsing to be abnormal;
### Current solution:
Add `xxxKeyword.g4` and `xxxStatement.g4` to match the special syntax of `Preview SQL` without affecting the original syntax;
The content of `xxxKeyword.g4` is :
```g4
import Alphabet;
WS
: [ \t\r\n] + -> skip
;
PREVIEW
: P R E V I E W
;
SQLString
: WS.*
;
```
and the content of `xxxStatement.g4` is :
```g4
previewSQL
: PREVIEW sql
;
sql
: SQLString
;
```
But there are some effects:
1. `Preview SQL` cannot be included in CommonDistSQLStatement, a separate file is required;
2. An additional try catch is required in `DistSQLStatementParserEngine` (because the `preview` grammar cannot be combined with other rules), it may be changed from:
```java
public SQLStatement parse(final String sql) {
try {
return new CommonDistSQLStatementParserEngine().parse(sql);
} catch (final ParseCancellationException | SQLParsingException ignored) {
return new FeaturedDistSQLStatementParserEngine().parse(sql);
}
}
```
to
```java
public SQLStatement parse(final String sql) {
try {
return new CommonDistSQLStatementParserEngine().parse(sql);
} catch (final ParseCancellationException | SQLParsingException ignored) {
try {
return new FeaturedDistSQLStatementParserEngine().parse(sql);
} catch (final SQLParsingException ignoredToo) {
return new XXXDistSQLStatementParserEngine().parse(sql);
}
}
}
```
3. At the same time, `xxx` now only has `preview grammar`, and will include `parse` and `optimize` in the future.
So we need to think of a good name. What about `Special` or `CommonDistSQL2`?
The above are the problems encountered in the design of `Preview SQL` grammar and the solution at present. I hope to get good suggestions, thank you!
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[GitHub] [shardingsphere] terrymanu commented on issue #11784: [DISCUSS] design a grammar for `Preview SQL`
Posted by GitBox <gi...@apache.org>.
terrymanu commented on issue #11784:
URL: https://github.com/apache/shardingsphere/issues/11784#issuecomment-897546052
CommonDistSQL2 is fine, I prefer it.
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[GitHub] [shardingsphere] RaigorJiang commented on issue #11784: [DISCUSS] design a grammar for `Preview SQL`
Posted by GitBox <gi...@apache.org>.
RaigorJiang commented on issue #11784:
URL: https://github.com/apache/shardingsphere/issues/11784#issuecomment-898100565
Let's call it `AdvancedDistSQL` first, and replace it with a better name in the future.
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[GitHub] [shardingsphere] RaigorJiang commented on issue #11784: [DISCUSS] design a grammar for `Preview SQL`
Posted by GitBox <gi...@apache.org>.
RaigorJiang commented on issue #11784:
URL: https://github.com/apache/shardingsphere/issues/11784#issuecomment-897548326
> CommonDistSQL2 is fine, I prefer it.
Thanks for your advice.
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[GitHub] [shardingsphere] RaigorJiang commented on issue #11784: [DISCUSS] design a grammar for `Preview SQL`
Posted by GitBox <gi...@apache.org>.
RaigorJiang commented on issue #11784:
URL: https://github.com/apache/shardingsphere/issues/11784#issuecomment-897532727
Suddenly I have a new idea, wait for me to try again. 😀
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[GitHub] [shardingsphere] RaigorJiang closed issue #11784: [DISCUSS] design a grammar for `Preview SQL`
Posted by GitBox <gi...@apache.org>.
RaigorJiang closed issue #11784:
URL: https://github.com/apache/shardingsphere/issues/11784
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