JDBC ResultSet get columns with table alias

Question

Imagine I have a query like

SELECT * from table1 a, table2 b where (WHATEVER)

Maybe both tables have the same column name. So I though it

Answer 1

One idea I had is to use the getTableName(iCol) to grab the table names for the duplicately-named columns, then wrap a hash of your own keys (with the table name prefix) that would point you to the correct column index, and reference your column-values that way. This would require an initial loop through the meta data at the beginning to set up. The only issue I see with this is that you are aliasing the table names as well. I've yet to find a way of getting those table name aliases from jdbc without managing it yourself when you build the sql statement. This solution would depend on what the syntactical pay-off would be to you.

Answer 2

If you are using MySQL just add

&useOldAliasMetadataBehavior=true

to your connectionString.

Afterwards you can use this little Helper:

import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.HashMap;
import java.util.Map;

public class ResultSetHelper {

    private final Map<String, Integer> columnMap;

    public ResultSetHelper(ResultSet rs) throws SQLException {
        this.columnMap = new HashMap<>();
        ResultSetMetaData md = rs.getMetaData();
        int columnCount = md.getColumnCount();
        for (int index = 1; index <= columnCount; index++) {
            String columnName = md.getColumnLabel(index);
            if (!columnMap.containsKey(columnName)) {
                columnMap.put(columnName, index);
            }

            String tableAlias = md.getTableName(index);
            if (tableAlias != null && !tableAlias.trim().isEmpty()) {
                columnMap.put(tableAlias + "." + columnName, index);
            }
        }
    }

    public Integer getColumnIndex(String columnName) {
        return columnMap.get(columnName);
    }

    public Integer getColumnIndex(String tableAlias, String columnName) {
        return columnMap.get(tableAlias + "." + columnName);
    }

}

Answer 3

Use column aliases like:

SELECT A.ID 'A_ID', B.ID 'B_ID' FROM TABLE1 AS A, TABLE2 AS B...

And specify all the columns you are retrieving (is a good practice).

Answer 4

ResultSetMetadata.getColumnLabel() is what you need

(edit) sample example, as stated by bharal in comment

SELECT * from table1 a, table2 b where (WHATEVER)

ResultSetMetaData rsmd = rset.getMetaData();
rsmd.getColumnLabel(1);

Answer 5

You can use alias on SQL level. Then you retrieve data by indexes. (But this approach will make maintenance a real nightmare)

SELECT a.column, b.column FROM table1 a, table2 b

String value = rs.getString(1);

Answer 6

Ok, it seems there's no method like resultSet.getString("a.columnName"); and you have to alias your columns at sql level, but inasmuch as there's a getTableName(iCol) method I hope guys at java.sql.ResultSet add such a feature.