Sleepy0521 commented on PR #160:
URL:
https://github.com/apache/flink-connector-jdbc/pull/160#issuecomment-2817430890
> I agree with @davidradl — `JdbcDynamicTableSource` should not have any
direct reference to a specific dialect, and we need to add a unit test for
this..
>
> Since we're assuming that getLimitClause will always append the clause at
the end of the query, I suggest introducing a new method in `JdbcDialect`:
>
> ```
> String addLimitClause(String query, long limit);
> ```
>
> We can then provide a default implementation in `AbstractDialect`:
>
> ```
> @Override
> public String addLimitClause(String query, long limit) {
> return String.format("%s %s", query, dialect.getLimitClause(limit));
> }
> ```
>
> Changing in `JdbcDynamicTableSource`
>
> ```
> if (limit >= 0) {
> query = dialect.addLimitClause(query, limit);
> }
> ```
>
> For dialects like SQL Server, this method can be overridden to inject the
limit clause appropriately. For example:
>
> ```
> // SqlServerDialect
> @Override
> public String addLimitClause(String query, long limit) {
> return query.replace("SELECT", String.format("SELECT TOP %s", limit));
> }
> ```
>
> Optionally, the `if (limit >= 0)` check in `JdbcDynamicTableSource` could
be moved into this new method for better encapsulation, but I’ve left it out
here for simplicity.
Good idea I commit again. please check it
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