Copy schema and create new schema with different name in the same data base

Question

I there a way to copy the existing schema and generate new schema with another name in the same database in postgres.

Answer 1

• If by copy schema you mean copy a database, then just use TEMPLATE option to create a copy: CREATE DATABASE dbname_target TEMPLATE dbname_source;

This will copy data too. So you might want to create your own template if you need many copies. See Template Databases.

• If you need only schema, then I suggest that you put your DB DDL scripts under source control (which is a good idea anyways) and have a separate (templated) script which will create the schema for you. Basically you have one SQL file, where you replace a ${schema_name} with your new schema name, and then execute this script on the database. In this way if you make a changes to this schema, you can also have scripts to update the schema to a new version, which you will have to do for every user schema in this case.

Answer 2

Check out this PostgreSQL's wiki page. It contains a function for clone_schema as you required, but this function only clones tables. The page refers to this post, which contains a function that clones everything you need for the schema. This function worked well for me, I managed to execute it with JDBC API.

But I had some problems when the schema names contained - or capital letters. After a research I found out that the source of the problem is quote_ident() method. I changes the clone_schema function to work with any schema names. I share the new function here, hope it will help somebody:

-- Function: clone_schema(text, text)

-- DROP FUNCTION clone_schema(text, text);

CREATE OR REPLACE FUNCTION clone_schema(
    source_schema text,
    dest_schema text,
    include_recs boolean)
  RETURNS void AS
$BODY$

--  This function will clone all sequences, tables, data, views & functions from any existing schema to a new one
-- SAMPLE CALL:
-- SELECT clone_schema('public', 'new_schema', TRUE);

DECLARE
  src_oid          oid;
  tbl_oid          oid;
  func_oid         oid;
  object           text;
  buffer           text;
  srctbl           text;
  default_         text;
  column_          text;
  qry              text;
  dest_qry         text;
  v_def            text;
  seqval           bigint;
  sq_last_value    bigint;
  sq_max_value     bigint;
  sq_start_value   bigint;
  sq_increment_by  bigint;
  sq_min_value     bigint;
  sq_cache_value   bigint;
  sq_log_cnt       bigint;
  sq_is_called     boolean;
  sq_is_cycled     boolean;
  sq_cycled        char(10);

BEGIN

-- Check that source_schema exists
  SELECT oid INTO src_oid
    FROM pg_namespace
   WHERE nspname = source_schema;
  IF NOT FOUND
    THEN 
    RAISE EXCEPTION 'source schema % does not exist!', source_schema;
    RETURN ;
  END IF;

  -- Check that dest_schema does not yet exist
  PERFORM nspname 
    FROM pg_namespace
   WHERE nspname = dest_schema;
  IF FOUND
    THEN 
    RAISE EXCEPTION 'dest schema % already exists!', dest_schema;
    RETURN ;
  END IF;

  EXECUTE 'CREATE SCHEMA "' || dest_schema || '"';

  -- Create sequences
  -- TODO: Find a way to make this sequence's owner is the correct table.
  FOR object IN
    SELECT sequence_name::text 
      FROM information_schema.sequences
     WHERE sequence_schema = source_schema
  LOOP
    EXECUTE 'CREATE SEQUENCE "' || dest_schema || '".' || quote_ident(object);
    srctbl := '"' || source_schema || '".' || quote_ident(object);

    EXECUTE 'SELECT last_value, max_value, start_value, increment_by, min_value, cache_value, log_cnt, is_cycled, is_called 
              FROM "' || source_schema || '".' || quote_ident(object) || ';' 
              INTO sq_last_value, sq_max_value, sq_start_value, sq_increment_by, sq_min_value, sq_cache_value, sq_log_cnt, sq_is_cycled, sq_is_called ; 

    IF sq_is_cycled 
      THEN 
        sq_cycled := 'CYCLE';
    ELSE
        sq_cycled := 'NO CYCLE';
    END IF;

    EXECUTE 'ALTER SEQUENCE "'   || dest_schema || '".' || quote_ident(object) 
            || ' INCREMENT BY ' || sq_increment_by
            || ' MINVALUE '     || sq_min_value 
            || ' MAXVALUE '     || sq_max_value
            || ' START WITH '   || sq_start_value
            || ' RESTART '      || sq_min_value 
            || ' CACHE '        || sq_cache_value 
            || sq_cycled || ' ;' ;

    buffer := '"' || dest_schema || '".' || quote_ident(object);
    IF include_recs 
        THEN
            EXECUTE 'SELECT setval( ''' || buffer || ''', ' || sq_last_value || ', ' || sq_is_called || ');' ; 
    ELSE
            EXECUTE 'SELECT setval( ''' || buffer || ''', ' || sq_start_value || ', ' || sq_is_called || ');' ;
    END IF;

  END LOOP;

-- Create tables 
  FOR object IN
    SELECT TABLE_NAME::text 
      FROM information_schema.tables 
     WHERE table_schema = source_schema
       AND table_type = 'BASE TABLE'

  LOOP
    buffer := '"' || dest_schema || '".' || quote_ident(object);
    EXECUTE 'CREATE TABLE ' || buffer || ' (LIKE "' || source_schema || '".' || quote_ident(object) 
        || ' INCLUDING ALL)';

    IF include_recs 
      THEN 
      -- Insert records from source table
      EXECUTE 'INSERT INTO ' || buffer || ' SELECT * FROM "' || source_schema || '".' || quote_ident(object) || ';';
    END IF;

    FOR column_, default_ IN
      SELECT column_name::text, 
             REPLACE(column_default::text, source_schema, dest_schema) 
        FROM information_schema.COLUMNS 
       WHERE table_schema = dest_schema 
         AND TABLE_NAME = object 
         AND column_default LIKE 'nextval(%"' || source_schema || '"%::regclass)'
    LOOP
      EXECUTE 'ALTER TABLE ' || buffer || ' ALTER COLUMN ' || column_ || ' SET DEFAULT ' || default_;
    END LOOP;

  END LOOP;

--  add FK constraint
  FOR qry IN
    SELECT 'ALTER TABLE "' || dest_schema || '".' || quote_ident(rn.relname) 
                          || ' ADD CONSTRAINT ' || quote_ident(ct.conname) || ' ' || pg_get_constraintdef(ct.oid) || ';'
      FROM pg_constraint ct
      JOIN pg_class rn ON rn.oid = ct.conrelid
     WHERE connamespace = src_oid
       AND rn.relkind = 'r'
       AND ct.contype = 'f'

    LOOP
      EXECUTE qry;

    END LOOP;


-- Create views 
  FOR object IN
    SELECT table_name::text,
           view_definition 
      FROM information_schema.views
     WHERE table_schema = source_schema

  LOOP
    buffer := '"' || dest_schema || '".' || quote_ident(object);
    SELECT view_definition INTO v_def
      FROM information_schema.views
     WHERE table_schema = source_schema
       AND table_name = quote_ident(object);

    EXECUTE 'CREATE OR REPLACE VIEW ' || buffer || ' AS ' || v_def || ';' ;

  END LOOP;

-- Create functions 
  FOR func_oid IN
    SELECT oid
      FROM pg_proc 
     WHERE pronamespace = src_oid

  LOOP      
    SELECT pg_get_functiondef(func_oid) INTO qry;
    SELECT replace(qry, source_schema, dest_schema) INTO dest_qry;
    EXECUTE dest_qry;

  END LOOP;

  RETURN; 

END;

$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;
ALTER FUNCTION clone_schema(text, text, boolean)
  OWNER TO postgres;