Do clean-up before columnar_create to make it runnable multiple times

So that flaky test detector can run columnar_create.sql multiple times.

src/test/regress/expected/columnar_create.out

@@ -1,24 +1,50 @@
 --
 -- Test the CREATE statements related to columnar.
 --
+-- We cannot create below tables within columnar_create because columnar_create
+-- is dropped at the end of this test but unfortunately some other tests depend
+-- those tables too.
+--
+-- However, this file has to be runnable multiple times for flaky test detection;
+-- so we create them below --outside columnar_create-- idempotantly.
+DO
+$$
+BEGIN
+IF NOT EXISTS (
+    SELECT 1 FROM pg_class
+    WHERE relname = 'contestant' AND
+          relnamespace = (
+            SELECT oid FROM pg_namespace WHERE nspname = 'public'
+          )
+   )
+THEN
     -- Create uncompressed table
     CREATE TABLE contestant (handle TEXT, birthdate DATE, rating INT,
         percentile FLOAT, country CHAR(3), achievements TEXT[])
         USING columnar;
     ALTER TABLE contestant SET (columnar.compression = none);
+
     CREATE INDEX contestant_idx on contestant(handle);
+
     -- Create zstd compressed table
     CREATE TABLE contestant_compressed (handle TEXT, birthdate DATE, rating INT,
         percentile FLOAT, country CHAR(3), achievements TEXT[])
         USING columnar;
+
     -- Test that querying an empty table works
     ANALYZE contestant;
+END IF;
+END
+$$
+LANGUAGE plpgsql;
 SELECT count(*) FROM contestant;
  count
 ---------------------------------------------------------------------
      0
 (1 row)
 
+CREATE SCHEMA columnar_create;
+SET search_path TO columnar_create;
 -- Should fail: unlogged tables not supported
 CREATE UNLOGGED TABLE columnar_unlogged(i int) USING columnar;
 ERROR:  unlogged columnar tables are not supported
@@ -156,6 +182,7 @@ SELECT columnar.get_storage_id(oid) AS columnar_temp_storage_id
 FROM pg_class WHERE relname='columnar_temp' \gset
 SELECT pg_backend_pid() AS val INTO old_backend_pid;
 \c - - - :master_port
+SET search_path TO columnar_create;
 -- wait until old backend to expire to make sure that temp table cleanup is complete
 SELECT columnar_test_helpers.pg_waitpid(val) FROM old_backend_pid;
  pg_waitpid
@@ -265,3 +292,5 @@ SELECT columnar_test_helpers.columnar_metadata_has_storage_id(:columnar_temp_sto
 
 -- make sure citus_columnar can be loaded
 LOAD 'citus_columnar';
+SET client_min_messages TO WARNING;
+DROP SCHEMA columnar_create CASCADE;

src/test/regress/sql/columnar_create.sql

@@ -2,7 +2,23 @@
 -- Test the CREATE statements related to columnar.
 --
 
-
+-- We cannot create below tables within columnar_create because columnar_create
+-- is dropped at the end of this test but unfortunately some other tests depend
+-- those tables too.
+--
+-- However, this file has to be runnable multiple times for flaky test detection;
+-- so we create them below --outside columnar_create-- idempotantly.
+DO
+$$
+BEGIN
+IF NOT EXISTS (
+    SELECT 1 FROM pg_class
+    WHERE relname = 'contestant' AND
+          relnamespace = (
+            SELECT oid FROM pg_namespace WHERE nspname = 'public'
+          )
+   )
+THEN
     -- Create uncompressed table
     CREATE TABLE contestant (handle TEXT, birthdate DATE, rating INT,
         percentile FLOAT, country CHAR(3), achievements TEXT[])
@@ -18,8 +34,16 @@ CREATE TABLE contestant_compressed (handle TEXT, birthdate DATE, rating INT,
 
     -- Test that querying an empty table works
     ANALYZE contestant;
+END IF;
+END
+$$
+LANGUAGE plpgsql;
+
 SELECT count(*) FROM contestant;
 
+CREATE SCHEMA columnar_create;
+SET search_path TO columnar_create;
+
 -- Should fail: unlogged tables not supported
 CREATE UNLOGGED TABLE columnar_unlogged(i int) USING columnar;
 
@@ -118,6 +142,7 @@ FROM pg_class WHERE relname='columnar_temp' \gset
 SELECT pg_backend_pid() AS val INTO old_backend_pid;
 
 \c - - - :master_port
+SET search_path TO columnar_create;
 
 -- wait until old backend to expire to make sure that temp table cleanup is complete
 SELECT columnar_test_helpers.pg_waitpid(val) FROM old_backend_pid;
@@ -184,3 +209,6 @@ SELECT columnar_test_helpers.columnar_metadata_has_storage_id(:columnar_temp_sto
 
 -- make sure citus_columnar can be loaded
 LOAD 'citus_columnar';
+
+SET client_min_messages TO WARNING;
+DROP SCHEMA columnar_create CASCADE;