should clear data at the start of each run

geocoder/admin0/sql/build_synonym_table.sql

@@ -1,5 +1,9 @@
 
 ---- ADMIN0_SYNONYMS ---
+
+-- clear all existing data from the table --
+DELETE FROM admin0_synonyms;
+
 -- insert data from ne_admin_0 into admin0_synonyms
 -- the name column from ne_10m_countries is assigned a rank of 0
 INSERT INTO admin0_synonyms (name, rank, adm0_a3)
@@ -79,4 +83,4 @@ DELETE FROM admin0_synonyms
                 FROM admin0_synonyms 
                 WHERE name_ = a.name_ 
                   AND adm0_a3 = a.adm0_a3 
-                  AND rank < a.rank));
+                  AND rank < a.rank));