diff --git a/sql/upgrades/146.sql b/sql/upgrades/146.sql
new file mode 100644
--- /dev/null
+++ b/sql/upgrades/146.sql
@@ -0,0 +1,115 @@
+-- SWH DB schema upgrade
+-- from_version: 145
+-- to_version: 146
+-- description: Improve query on origin_visit
+
+-- latest schema version
+insert into dbversion(version, release, description)
+      values(146, now(), 'Work In Progress');
+
+-- create a temporary table called tmp_TBLNAME, mimicking existing table
+-- TBLNAME
+--
+-- Args:
+--     tblname: name of the table to mimic
+create or replace function swh_mktemp(tblname regclass)
+    returns void
+    language plpgsql
+as $$
+begin
+    execute format('
+	create temporary table if not exists tmp_%1$I
+	    (like %1$I including defaults)
+	    on commit delete rows;
+      alter table tmp_%1$I drop column if exists object_id;
+	', tblname);
+    return;
+end
+$$;
+
+-- create a temporary table for directory entries called tmp_TBLNAME,
+-- mimicking existing table TBLNAME with an extra dir_id (sha1_git)
+-- column, and dropping the id column.
+--
+-- This is used to create the tmp_directory_entry_<foo> tables.
+--
+-- Args:
+--     tblname: name of the table to mimic
+create or replace function swh_mktemp_dir_entry(tblname regclass)
+    returns void
+    language plpgsql
+as $$
+begin
+    execute format('
+	create temporary table if not exists tmp_%1$I
+	    (like %1$I including defaults, dir_id sha1_git)
+	    on commit delete rows;
+        alter table tmp_%1$I drop column if exists id;
+	', tblname);
+    return;
+end
+$$;
+
+-- create a temporary table for revisions called tmp_revisions,
+-- mimicking existing table revision, replacing the foreign keys to
+-- people with an email and name field
+--
+create or replace function swh_mktemp_revision()
+    returns void
+    language sql
+as $$
+    create temporary table if not exists tmp_revision (
+        like revision including defaults,
+        author_fullname bytea,
+        author_name bytea,
+        author_email bytea,
+        committer_fullname bytea,
+        committer_name bytea,
+        committer_email bytea
+    ) on commit delete rows;
+    alter table tmp_revision drop column if exists author;
+    alter table tmp_revision drop column if exists committer;
+    alter table tmp_revision drop column if exists object_id;
+$$;
+
+-- create a temporary table for releases called tmp_release,
+-- mimicking existing table release, replacing the foreign keys to
+-- people with an email and name field
+--
+create or replace function swh_mktemp_release()
+    returns void
+    language sql
+as $$
+    create temporary table if not exists tmp_release (
+        like release including defaults,
+        author_fullname bytea,
+        author_name bytea,
+        author_email bytea
+    ) on commit delete rows;
+    alter table tmp_release drop column if exists author;
+    alter table tmp_release drop column if exists object_id;
+  ) on commit delete rows;
+$$;
+
+-- create a temporary table for the branches of a snapshot
+create or replace function swh_mktemp_snapshot_branch()
+    returns void
+    language sql
+as $$
+  create temporary table if not exists tmp_snapshot_branch (
+      name bytea not null,
+      target bytea,
+      target_type snapshot_target
+  ) on commit delete rows;
+$$;
+
+-- create a temporary table for the tools
+create or replace function swh_mktemp_tool()
+    returns void
+    language sql
+as $$
+    create temporary table if not exists tmp_tool (
+      like tool including defaults
+    ) on commit delete rows;
+    alter table tmp_tool drop column if exists id;
+$$;
diff --git a/swh/storage/sql/30-swh-schema.sql b/swh/storage/sql/30-swh-schema.sql
--- a/swh/storage/sql/30-swh-schema.sql
+++ b/swh/storage/sql/30-swh-schema.sql
@@ -17,7 +17,7 @@
 
 -- latest schema version
 insert into dbversion(version, release, description)
-      values(145, now(), 'Work In Progress');
+      values(146, now(), 'Work In Progress');
 
 -- a SHA1 checksum
 create domain sha1 as bytea check (length(value) = 20);
diff --git a/swh/storage/sql/40-swh-func.sql b/swh/storage/sql/40-swh-func.sql
--- a/swh/storage/sql/40-swh-func.sql
+++ b/swh/storage/sql/40-swh-func.sql
@@ -17,9 +17,9 @@
 as $$
 begin
     execute format('
-	create temporary table tmp_%1$I
+	create temporary table if not exists tmp_%1$I
 	    (like %1$I including defaults)
-	    on commit drop;
+	    on commit delete rows;
       alter table tmp_%1$I drop column if exists object_id;
 	', tblname);
     return;
@@ -40,16 +40,15 @@
 as $$
 begin
     execute format('
-	create temporary table tmp_%1$I
+	create temporary table if not exists tmp_%1$I
 	    (like %1$I including defaults, dir_id sha1_git)
-	    on commit drop;
-        alter table tmp_%1$I drop column id;
+	    on commit delete rows;
+        alter table tmp_%1$I drop column if exists id;
 	', tblname);
     return;
 end
 $$;
 
-
 -- create a temporary table for revisions called tmp_revisions,
 -- mimicking existing table revision, replacing the foreign keys to
 -- people with an email and name field
@@ -58,7 +57,7 @@
     returns void
     language sql
 as $$
-    create temporary table tmp_revision (
+    create temporary table if not exists tmp_revision (
         like revision including defaults,
         author_fullname bytea,
         author_name bytea,
@@ -66,13 +65,12 @@
         committer_fullname bytea,
         committer_name bytea,
         committer_email bytea
-    ) on commit drop;
-    alter table tmp_revision drop column author;
-    alter table tmp_revision drop column committer;
-    alter table tmp_revision drop column object_id;
+    ) on commit delete rows;
+    alter table tmp_revision drop column if exists author;
+    alter table tmp_revision drop column if exists committer;
+    alter table tmp_revision drop column if exists object_id;
 $$;
 
-
 -- create a temporary table for releases called tmp_release,
 -- mimicking existing table release, replacing the foreign keys to
 -- people with an email and name field
@@ -81,14 +79,14 @@
     returns void
     language sql
 as $$
-    create temporary table tmp_release (
+    create temporary table if not exists tmp_release (
         like release including defaults,
         author_fullname bytea,
         author_name bytea,
         author_email bytea
-    ) on commit drop;
-    alter table tmp_release drop column author;
-    alter table tmp_release drop column object_id;
+    ) on commit delete rows;
+    alter table tmp_release drop column if exists author;
+    alter table tmp_release drop column if exists object_id;
 $$;
 
 -- create a temporary table for the branches of a snapshot
@@ -96,24 +94,24 @@
     returns void
     language sql
 as $$
-  create temporary table tmp_snapshot_branch (
+  create temporary table if not exists tmp_snapshot_branch (
       name bytea not null,
       target bytea,
       target_type snapshot_target
-  ) on commit drop;
+  ) on commit delete rows;
 $$;
 
+-- create a temporary table for the tools
 create or replace function swh_mktemp_tool()
     returns void
     language sql
 as $$
-    create temporary table tmp_tool (
+    create temporary table if not exists tmp_tool (
       like tool including defaults
-    ) on commit drop;
-    alter table tmp_tool drop column id;
+    ) on commit delete rows;
+    alter table tmp_tool drop column if exists id;
 $$;
 
-
 -- a content signature is a set of cryptographic checksums that we use to
 -- uniquely identify content, for the purpose of verifying if we already have
 -- some content or not during content injection