Thanks your explanation, Julian. Does it mean the optimization of this JDBC
interface may be included in next release of Calcite?
Juan Pan (Trista)
Senior DBA & PPMC of Apache ShardingSphere(Incubating)
E-mail: [email protected]
On 01/7/2020 11:17，Julian Hyde<[email protected]> wrote：
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]
