Yes, we should be returning “” rather than null. (Not an excuse, but that method is so old that I suspect that the authors of JDBC were still thinking in terms of ODBC. In C it’s difficult to return a null, it’s easier to return an empty string.)
Julian > On Jan 6, 2020, at 7:03 PM, Juan Pan <[email protected]> wrote: > > FYI. > > > The following information comes from `java.sql.ResultSetMetaData`. > > > /** > * Gets the designated column's table name. > * > * @param column the first column is 1, the second is 2, ... > * @return table name or "" if not applicable > * @exception SQLException if a database access error occurs > */ > String getTableName(int column) throws SQLException; > > > Juan Pan (Trista) > > Senior DBA & PPMC of Apache ShardingSphere(Incubating) > E-mail: [email protected] > > > > > On 01/7/2020 10:56，Juan Pan<[email protected]> wrote： > Hi Julian, > > > You’re right. From my tests, since “a” is not from table test, > getTableName(columnIndex) returns `empty string` from MySQL and H2 databases, > and `null` from calcite. It makes sense. > The scenario happened to me is that some of third-part applications or > open-source projects would call some jdbc interfaces, like > getTableName(columnIndex). > As a result, when they call getTableName(columnIndex), the null result from > calcite makes them throw NPE, but empty string from DBs avoid this case. > > > Julian, very appreciated your help. :-) > > > Best wishes, > Trista > > > Juan Pan (Trista) > > Senior DBA & PPMC of Apache ShardingSphere(Incubating) > E-mail: [email protected] > > > > > On 01/7/2020 04:12，Julian Hyde<[email protected]> wrote： > JDBC table names and column names are of limited use. They tell you where a > particular column comes from, and your “a” column does not come (directly) > from a table. I think you’ll find that Calcite is implementing the JDBC > standard correctly, and is consistent with other databases. > > What do you need the table name for? > > If you want to understand the structure of the query - e.g. the fact that the > query is sourced from the “test” table - then your might be better working > with the SqlNode or RelNode representations. The RelNode representation of > your query is > > > Aggregate(count(*) as a) > ^ > | > TableScan(“test”) > > and that probably tells you what you need to know. > > Julian > > > On Jan 5, 2020, at 11:42 PM, Juan Pan <[email protected]> wrote: > > > > Hi Calcite Community, > > > Thanks for your attention. After failing self-helping by debug source code, i > sent this email for your help. :) > > > My query SQL is `SELECT count(*) a FROM test`, and i called JDBC interface, > i.e, `ResultSet.getMetaData().getTableName(1)` to get table name, i.e, test, > however the result of which is null. > I traced the process and found that if !(selectItem instanceof SqlIdentifier) > then return null in `SqlValidatorImpl.java`. Is there any way to get the real > table name, i.e, test? > > > Thanks in advance, > > > Trista > > > > > > > Juan Pan (Trista) > > Senior DBA & PPMC of Apache ShardingSphere(Incubating) > E-mail: [email protected] > > >
