diff --git a/model/ddl.sql b/model/ddl.sql
index 9e13b52..9f15d26 100644
--- a/model/ddl.sql
+++ b/model/ddl.sql
@@ -35,7 +35,9 @@ CREATE TABLE PUBLIC.GRID (
     NAME VARCHAR(64) NOT NULL DEFAULT '',
     DESCRIPTION VARCHAR(512) NOT NULL DEFAULT '',
     OP INTEGER NOT NULL DEFAULT -1,
-    TS TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP
+    TS TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    UNIQUE (TAGNAME)
 );
 
 CREATE TABLE PUBLIC.ZONE (
@@ -47,6 +49,8 @@ CREATE TABLE PUBLIC.ZONE (
     OP INTEGER NOT NULL DEFAULT -1,
     TS TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
 
+    UNIQUE (TAGNAME),
+
     FOREIGN KEY (GRID_ID) REFERENCES PUBLIC.GRID (ID)
 );
 
@@ -60,6 +64,8 @@ CREATE TABLE PUBLIC.STATION (
     OP INTEGER NOT NULL DEFAULT -1,
     TS TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
 
+    UNIQUE (TAGNAME),
+
     FOREIGN KEY (ZONE_ID) REFERENCES PUBLIC.ZONE (ID)
 );