select * into city 
from(
  values 
    (1, 'abc', 1),
    (2, 'xyz', 2),
    (3, 'efg', 2),
    (4, 'hij', 3),
    (5, 'klm', 4),
    (6, 'nop', 1),
    (7, 'qrs', 2),
    (8, 'tuv', 3),
    (9, 'wxy', 3),
    (10, 'zab', 2),
    (11, 'cde', 2),
    (12, 'fgh', 1),
    (13, 'ijk', 5)
) AS t(id, name, code);

select * into Address
from(
  values 
   (1, 1, 'wer'),
   (2, 2, 'sdf'),
   (3, 3, 'tyu'),
   (4, 4, 'dsf'),
   (5, 5, 'shr'),
   (6, 6, 'wdg'),
   (7, 7, 'gkw'),
   (8, 8, 'tgt'),
   (9, 9, 'okt'),
   (10, 10, 'lam'),
   (11, 11, 'atw'),
   (12, 12, 'goe'),
   (13, 13, 'awk'),
   (14, 7, 'war'),
   (15, 11, 'dfo')
) AS t(id, city_id, name);

CREATE OR REPLACE PROCEDURE delete_dulicate_city()
LANGUAGE 'plpgsql'
AS $$
BEGIN
    DROP TABLE IF EXISTS temp_city;

    CREATE TEMPORARY TABLE IF NOT EXISTS temp_city
    (
        id_to                      INT,
        id_from                    INT
    );
        
    INSERT INTO temp_city
    SELECT c1.id id_to, c2.id id_from 
    FROM
    (
        SELECT id, code, row_number() over(partition BY code ORDER BY id) rn
        FROM city
    ) c1 
    INNER JOIN city c2 
    ON  c1.rn = 1
    AND c1.code=c2.code 
    AND c2.id > c1.id;

    UPDATE address a
    SET city_id = tc.id_to
    FROM temp_city tc
    WHERE a.city_id=tc.id_from;

    DELETE FROM city 
    WHERE id IN (SELECT id_from FROM temp_city);
END;
$$;

CALL delete_dulicate_city();

SELECT * FROM city;
SELECT * FROM Address ORDER BY id;

PostgreSQL online editor

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About PostgreSQL

PostgreSQL is a open source relational database system and is also knows as Postgres.

Key Features:

  • Postgres is not only free and open-source but also it is highly extensible.
  • Custom Data types and funtions from various programming languaues can be introduced and the good part is compiling entire database is not required.
  • ACID(Atomicity, Consistency, Isolation, Durability) compliant.
  • First DBMS which implemented Multi-version concurrency control (MVCC) feature.
  • It's the default database server for MacOS.
  • It supports all major operating systems like Linux, Windows, OpenBSD,FreeBSD etc.

Syntax help

1. CREATE

CREATE command is used to create a table, schema or an index.

Syntax:

         CREATE TABLE table_name (
                column1 datatype,
                column2 datatype,
                ....);

2. ALTER

ALTER command is used to add, modify or delete columns or constraints from the database table.

Syntax

ALTER TABLE Table_name ADD column_name datatype;

3. TRUNCATE:

TRUNCATE command is used to delete the data present in the table but this will not delete the table.

Syntax

TRUNCATE table table_name;

4. DROP

DROP command is used to delete the table along with its data.

Syntax

DROP TABLE table_name;

5. RENAME

RENAME command is used to rename the table name.

Syntax

ALTER TABLE table_name1 RENAME to new_table_name1;

6. INSERT

INSERT Statement is used to insert new records into the database table.

Syntax

INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);

7. SELECT

Select statement is used to select data from database tables.

Syntax:

SELECT column1, column2, ...
FROM table_name;

8. UPDATE

UPDATE statement is used to modify the existing values of records present in the database table.

Syntax

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

9. DELETE

DELETE statement is used to delete the existing records present in the database table.

Syntax

DELETE FROM table_name where condition;