Index: ext/rbu/rbudiff.test
==================================================================
--- ext/rbu/rbudiff.test
+++ ext/rbu/rbudiff.test
@@ -51,50 +51,79 @@
   rbudb close
   step_rbu $target rbu.db
 }
 
 proc rbudiff_cksum {db1} {
+  set txt ""
+
   sqlite3 dbtmp $db1
-  set txt [dbtmp eval {
-    SELECT a || '.' || b || '.' || c FROM t1 ORDER BY 1;
-    SELECT a || '.' || b || '.' || c FROM t2 ORDER BY 1;
-  }]
+  foreach tbl [dbtmp eval {SELECT name FROM sqlite_master WHERE type='table'}] {
+    append txt [dbtmp eval \
+      "SELECT a || '.' || b || '.' || c FROM $tbl ORDER BY 1"
+    ]
+  }
   dbtmp close
+
   md5 $txt
 }
 
-sqlite3 db test.db
-do_execsql_test 1.0 {
-  CREATE TABLE t1(a PRIMARY KEY, b, c);
-  INSERT INTO t1 VALUES(1, 2, 3);
-  INSERT INTO t1 VALUES(4, 5, 6);
-
-  CREATE TABLE t2(a, b, c, PRIMARY KEY(b, c));
-  INSERT INTO t2 VALUES(1, 2, 3);
-  INSERT INTO t2 VALUES(4, 5, 6);
-}
-
-db close
-forcedelete test.db2
-forcecopy test.db test.db2
-
-sqlite3 db test.db
-do_execsql_test 1.1 {
-  INSERT INTO t1 VALUES(7, 8, 9);
-  DELETE FROM t1 WHERE a=4;
-  UPDATE t1 SET c = 11 WHERE a = 1;
-
-  INSERT INTO t2 VALUES(7, 8, 9);
-  DELETE FROM t2 WHERE a=4;
-  UPDATE t2 SET c = 11 WHERE a = 1;
-}
-db close
-
-do_test 1.2 {
-  set sql [get_rbudiff_sql test.db test.db2]
-  apply_rbudiff $sql test.db
-} {SQLITE_DONE}
-
-do_test 1.3 { rbudiff_cksum test.db } [rbudiff_cksum test.db2]
+foreach {tn init mod} {
+  1 {
+    CREATE TABLE t1(a PRIMARY KEY, b, c);
+    INSERT INTO t1 VALUES(1, 2, 3);
+    INSERT INTO t1 VALUES(4, 5, 6);
+  
+    CREATE TABLE t2(a, b, c, PRIMARY KEY(b, c));
+    INSERT INTO t2 VALUES(1, 2, 3);
+    INSERT INTO t2 VALUES(4, 5, 6);
+  } {
+    INSERT INTO t1 VALUES(7, 8, 9);
+    DELETE FROM t1 WHERE a=4;
+    UPDATE t1 SET c = 11 WHERE a = 1;
+  
+    INSERT INTO t2 VALUES(7, 8, 9);
+    DELETE FROM t2 WHERE a=4;
+    UPDATE t2 SET c = 11 WHERE a = 1;
+  }
+
+  2 {
+    CREATE TABLE t1(a, b, c, PRIMARY KEY(a, b, c));
+    INSERT INTO t1 VALUES('u', 'v', 'w');
+    INSERT INTO t1 VALUES('x', 'y', 'z');
+  } {
+    DELETE FROM t1 WHERE a='u';
+    INSERT INTO t1 VALUES('a', 'b', 'c');
+  }
+
+} {
+  
+  catch { db close }
+
+  forcedelete test.db test.db2
+  sqlite3 db test.db
+  db eval "$init"
+  sqlite3 db test.db2
+  db eval "$init ; $mod"
+  db close
+
+  do_test 1.$tn.2 {
+    set sql [get_rbudiff_sql test.db test.db2]
+    apply_rbudiff $sql test.db
+  } {SQLITE_DONE}
+  do_test 1.$tn.3 { rbudiff_cksum test.db } [rbudiff_cksum test.db2]
+
+  forcedelete test.db test.db2
+  sqlite3 db test.db
+  db eval "$init ; $mod"
+  sqlite3 db test.db2
+  db eval "$init"
+  db close
+
+  do_test 1.$tn.4 {
+    set sql [get_rbudiff_sql test.db test.db2]
+    apply_rbudiff $sql test.db
+  } {SQLITE_DONE}
+  do_test 1.$tn.5 { rbudiff_cksum test.db } [rbudiff_cksum test.db2]
+}
 
 finish_test
 

Index: tool/sqldiff.c
==================================================================
--- tool/sqldiff.c
+++ tool/sqldiff.c
@@ -787,42 +787,48 @@
   strPrintf(pSql, "\n)");
 
   /* Deleted rows: */
   strPrintf(pSql, "\nUNION ALL\nSELECT ");
   strPrintfArray(pSql, ", ", "%s", azCol, nPK);
-  strPrintf(pSql, ", ");
-  strPrintfArray(pSql, ", ", "NULL", &azCol[nPK], -1);
+  if( azCol[nPK] ){
+    strPrintf(pSql, ", ");
+    strPrintfArray(pSql, ", ", "NULL", &azCol[nPK], -1);
+  }
   strPrintf(pSql, ", 1");         /* Set ota_control to 1 for a delete */
   strPrintf(pSql, " FROM main.%Q AS n WHERE NOT EXISTS (\n", zTab);
   strPrintf(pSql, "    SELECT 1 FROM ", zTab);
   strPrintf(pSql, " aux.%Q AS o WHERE ", zTab);
   strPrintfArray(pSql, " AND ", "(n.%Q IS o.%Q)", azCol, nPK);
   strPrintf(pSql, "\n) ");
 
-  /* Updated rows: */
-  strPrintf(pSql, "\nUNION ALL\nSELECT ");
-  strPrintfArray(pSql, ", ", "n.%s", azCol, nPK);
-  strPrintf(pSql, ",\n");
-  strPrintfArray(pSql, " ,\n", 
-      "    CASE WHEN n.%s IS o.%s THEN NULL ELSE n.%s END", &azCol[nPK], -1
-  );
-
-  if( bOtaRowid==0 ){
-    strPrintf(pSql, ", '");
-    strPrintfArray(pSql, "", ".", azCol, nPK);
-    strPrintf(pSql, "' ||\n");
-  }else{
-    strPrintf(pSql, ",\n");
-  }
-  strPrintfArray(pSql, " ||\n", 
-      "    CASE WHEN n.%s IS o.%s THEN '.' ELSE 'x' END", &azCol[nPK], -1
-  );
-  strPrintf(pSql, "\nAS ota_control");
-
-  strPrintf(pSql, "\nFROM main.%Q AS o, aux.%Q AS n\nWHERE ", zTab, zTab);
-  strPrintfArray(pSql, " AND ", "(n.%Q IS o.%Q)", azCol, nPK);
-  strPrintf(pSql, " AND ota_control LIKE '%%x%%'");
+  /* Updated rows. If all table columns are part of the primary key, there 
+  ** can be no updates. In this case this part of the compound SELECT can
+  ** be omitted altogether. */
+  if( azCol[nPK] ){
+    strPrintf(pSql, "\nUNION ALL\nSELECT ");
+    strPrintfArray(pSql, ", ", "n.%s", azCol, nPK);
+    strPrintf(pSql, ",\n");
+    strPrintfArray(pSql, " ,\n", 
+        "    CASE WHEN n.%s IS o.%s THEN NULL ELSE n.%s END", &azCol[nPK], -1
+    );
+
+    if( bOtaRowid==0 ){
+      strPrintf(pSql, ", '");
+      strPrintfArray(pSql, "", ".", azCol, nPK);
+      strPrintf(pSql, "' ||\n");
+    }else{
+      strPrintf(pSql, ",\n");
+    }
+    strPrintfArray(pSql, " ||\n", 
+        "    CASE WHEN n.%s IS o.%s THEN '.' ELSE 'x' END", &azCol[nPK], -1
+    );
+    strPrintf(pSql, "\nAS ota_control");
+
+    strPrintf(pSql, "\nFROM main.%Q AS o, aux.%Q AS n\nWHERE ", zTab, zTab);
+    strPrintfArray(pSql, " AND ", "(n.%Q IS o.%Q)", azCol, nPK);
+    strPrintf(pSql, " AND ota_control LIKE '%%x%%'");
+  }
 
   /* Now add an ORDER BY clause to sort everything by PK. */
   strPrintf(pSql, "\nORDER BY ");
   for(i=1; i<=nPK; i++) strPrintf(pSql, "%s%d", ((i>1)?", ":""), i);
 }