diff --git a/procedures/query/applyPOV.sql b/procedures/query/applyPOV.sql
index aab2eb19ca26c9393f7e972242a7649f1dd762d5..58fed6171869251939cb42fe8fb0df756fe417a6 100644
--- a/procedures/query/applyPOV.sql
+++ b/procedures/query/applyPOV.sql
@@ -24,7 +24,21 @@
 DROP PROCEDURE IF EXISTS db_2_0.applyPOV;
 DELIMITER //
 
-CREATE PROCEDURE db_2_0.applyPOV(in sourceSet VARCHAR(255), in targetSet VARCHAR(255), in propertiesTable VARCHAR(255), in refIdsTable VARCHAR(255), in o CHAR(4), in vText VARCHAR(255), in vInt INT, in vDouble DOUBLE, in unit_sig BIGINT, in vDoubleStdUnit DOUBLE, in stdUnit_sig BIGINT, in vDateTime VARCHAR(255), in vDateTimeDotNotation VARCHAR(255), in agg CHAR(3), in pname VARCHAR(255))
+CREATE PROCEDURE db_2_0.applyPOV(in sourceSet VARCHAR(255),
+                                 in targetSet VARCHAR(255),
+                                 in propertiesTable VARCHAR(255),
+                                 in refIdsTable VARCHAR(255),
+                                 in o CHAR(4),
+                                 in vText VARCHAR(255),
+                                 in vInt INT,
+                                 in vDouble DOUBLE,
+                                 in unit_sig BIGINT,
+                                 in vDoubleStdUnit DOUBLE,
+                                 in stdUnit_sig BIGINT,
+                                 in vDateTime VARCHAR(255),
+                                 in vDateTimeDotNotation VARCHAR(255),
+                                 in agg CHAR(3),
+                                 in pname VARCHAR(255))
 POV_LABEL: BEGIN
     DECLARE data TEXT DEFAULT NULL; /*data subselect statement string*/
     DECLARE sTextData VARCHAR(20000) DEFAULT NULL; /*SELECT PREFIX for data subselect plus WHERE CLAUSE for text_data*/
@@ -55,6 +69,18 @@ POV_LABEL: BEGIN
         #-- special case: property IS NOT NULL
         #-- generate statement parts
         SET vText = NULL;
+        /* Union of the following tables:
+             text_data
+             enum_data
+             integer_data
+             date_data
+             datetime_data
+             reference_data
+             double_data
+           Notes:
+             SELECT DISTINCT -> No duplicate values
+             UNION ALL -> Allow also duplicate values
+        */
         SET sTextData = 'SELECT DISTINCT domain_id, entity_id, property_id FROM `text_data` AS subdata WHERE subdata.value IS NOT NULL UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `enum_data` AS subdata WHERE subdata.value IS NOT NULL UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `integer_data` AS subdata WHERE subdata.value IS NOT NULL UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `double_data` AS subdata WHERE subdata.value IS NOT NULL UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `date_data` AS subdata WHERE subdata.value IS NOT NULL UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `datetime_data` AS subdata WHERE subdata.value IS NOT NULL UNION ALL SELECT DISTINCT domain_id, entity_id, property_id FROM `reference_data` AS subdata WHERE subdata.value IS NOT NULL';
 
     ELSEIF o = "(" or o = "!(" THEN