Reestablish warning on duplicate column in query.

Closes #1680
Original pull request #1825

Author: schauder

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/core/convert/RowDocumentResultSetExtractor.java

@@ -22,6 +22,8 @@
 import java.util.Iterator;
 import java.util.Map;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.dao.DataRetrievalFailureException;
 import org.springframework.data.jdbc.core.convert.RowDocumentExtractorSupport.AggregateContext;
 import org.springframework.data.jdbc.core.convert.RowDocumentExtractorSupport.RowDocumentSink;
@@ -43,6 +45,9 @@
  */
 class RowDocumentResultSetExtractor {
 
+	private static final Logger log = LoggerFactory.getLogger(RowDocumentResultSetExtractor.class);
+	public static final String DUPLICATE_COLUMN_WARNING = "ResultSet contains column \"{}\" multiple times. Later column index is {}";
+
 	private final RelationalMappingContext context;
 	private final PathToColumnMapping propertyToColumn;
 
@@ -66,9 +71,13 @@ static RowDocument toRowDocument(ResultSet resultSet) throws SQLException {
 		RowDocument document = new RowDocument(columnCount);
 
 		for (int i = 0; i < columnCount; i++) {
+
 			Object rsv = JdbcUtils.getResultSetValue(resultSet, i + 1);
 			String columnName = md.getColumnLabel(i + 1);
-			document.put(columnName, rsv instanceof Array a ? a.getArray() : rsv);
+			Object old = document.put(columnName, rsv instanceof Array a ? a.getArray() : rsv);
+			if (old != null) {
+				log.warn(DUPLICATE_COLUMN_WARNING, columnName, i);
+			}
 		}
 
 		return document;
@@ -107,7 +116,12 @@ public Map<String, Integer> getColumnMap(ResultSet result) {
 				Map<String, Integer> columns = new LinkedCaseInsensitiveMap<>(metaData.getColumnCount());
 
 				for (int i = 0; i < metaData.getColumnCount(); i++) {
-					columns.put(metaData.getColumnLabel(i + 1), i + 1);
+
+					String columnLabel = metaData.getColumnLabel(i + 1);
+					Object old = columns.put(columnLabel, i + 1);
+					if (old != null) {
+						log.warn(DUPLICATE_COLUMN_WARNING, columnLabel, i);
+					}
 				}
 				return columns;
 			} catch (SQLException e) {