updating table rows in postgres using subquery

Question

Using postgres 8.4, My goal is to update existing table:

CREATE TABLE public.dummy
(
  address_id SERIAL,
  addr1 character(40),
  addr2 character(40),
  ci         


        

Answer 1

There are many ways to update the rows.

When it comes to UPDATE the rows using subqueries, you can use any of these approaches.

1. Approach-1 [Using direct table reference]

UPDATE
  
SET
  customer=.customer,
  address=.address,
  partn=.partn
FROM
  
WHERE
  .address_id=.address_i;

Explanation: table1 is the table which we want to update, table2 is the table, from which we'll get the value to be replaced/updated. We are using FROM clause, to fetch the table2's data. WHERE clause will help to set the proper data mapping.

2. Approach-2 [Using SubQueries]

UPDATE
  
SET
  customer=subquery.customer,
  address=subquery.address,
  partn=subquery.partn
FROM
  (
    SELECT
      address_id, customer, address, partn
    FROM  /* big hairy SQL */ ...
  ) AS subquery
WHERE
  dummy.address_id=subquery.address_id;

Explanation: Here we are using subquerie inside the FROM clause, and giving an alias to it. So that it will act like the table.

3. Approach-3 [Using multiple Joined tables]

UPDATE
  
SET
  customer=.customer,
  address=.address,
  partn=.partn
FROM
   as t2
  JOIN  as t3
  ON
    t2.id = t3.id
WHERE
  .address_id=.address_i;

Explanation: Sometimes we face the situation in that table join is so important to get proper data for the update. To do so, Postgres allows us to Join multiple tables inside the FROM clause.

4. Approach-4 [Using WITH statement]

   • 4.1 [Using simple query]

WITH subquery AS (
    SELECT
      address_id,
      customer,
      address,
      partn
    FROM
      ;
)
UPDATE 
SET customer = subquery.customer,
    address  = subquery.address,
    partn    = subquery.partn
FROM subquery
WHERE .address_id = subquery.address_id;

• 4.2 [Using query with complex JOIN]

WITH subquery AS (
    SELECT address_id, customer, address, partn
    FROM
       as t1
    JOIN
       as t2
    ON
      t1.id = t2.id;
    -- You can build as COMPLEX as this query as per your need.
)
UPDATE 
SET customer = subquery.customer,
    address  = subquery.address,
    partn    = subquery.partn
FROM subquery
WHERE .address_id = subquery.address_id;

Explanation: From Postgres 9.1, this(WITH) concept has been introduces. Using that We can make any complex queries and generate desire result. Here we are using this approach to update the table.

I hope, this would be helpful.