[GitHub] [beam] ibzib commented on pull request #15373: [BEAM-12790] Add projection pushdown to JDBC SchemaIO.

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ibzib commented on pull request #15373:
URL: https://github.com/apache/beam/pull/15373#issuecomment-912820487


   @apilloud Escaping strings is difficult, since JDBC has to work with various [incompatible SQL implementations](https://stackoverflow.com/a/10574031/4400443). The answers to [this Stack Overflow question](https://stackoverflow.com/questions/2038169/how-to-quote-escape-identifiers-such-as-column-names-with-jdbc/64863308) suggest that we can learn the database's quoting syntax via the JDBC Connection. The good news is that we can access the Connection through the PreparedStatement in JdbcIO's [StatementPreparator](https://github.com/apache/beam/blob/c4e0b4ac0777f37f5eb775a8a83c56f66b3baac3/sdks/java/io/jdbc/src/main/java/org/apache/beam/sdk/io/jdbc/JdbcIO.java#L545-L552). The bad news is there's no way to change the query, aside from setting parameters, which cannot be used for column and table names.
   
   https://github.com/apache/beam/blob/c4e0b4ac0777f37f5eb775a8a83c56f66b3baac3/sdks/java/io/jdbc/src/main/java/org/apache/beam/sdk/io/jdbc/JdbcIO.java#L1168-L1173
   
   So to get this to work I think we would have to add a method to JdbcIO that takes a functional interface that takes a Connection and returns a fresh PreparedStatement.


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