updating table rows in postgres using subquery

If there are no performance gains using a join, then I prefer Common Table Expressions (CTEs) for readability:

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

IMHO a bit more modern.

Postgres allows:

UPDATE dummy
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;

This syntax is not standard SQL, but it is much more convenient for this type of query than standard SQL. I believe Oracle (at least) accepts something similar.

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
  <table1>
SET
  customer=<table2>.customer,
  address=<table2>.address,
  partn=<table2>.partn
FROM
  <table2>
WHERE
  <table1>.address_id=<table2>.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
  <table1>
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
  <table1>
SET
  customer=<table2>.customer,
  address=<table2>.address,
  partn=<table2>.partn
FROM
  <table2> as t2
  JOIN <table3> as t3
  ON
    t2.id = t3.id
WHERE
  <table1>.address_id=<table2>.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
      <table1>;
)
UPDATE <table-X>
SET customer = subquery.customer,
    address  = subquery.address,
    partn    = subquery.partn
FROM subquery
WHERE <table-X>.address_id = subquery.address_id;

• 4.2 [Using query with complex JOIN]

WITH subquery AS (
    SELECT address_id, customer, address, partn
    FROM
      <table1> as t1
    JOIN
      <table2> as t2
    ON
      t1.id = t2.id;
    -- You can build as COMPLEX as this query as per your need.
)
UPDATE <table-X>
SET customer = subquery.customer,
    address  = subquery.address,
    partn    = subquery.partn
FROM subquery
WHERE <table-X>.address_id = subquery.address_id;

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

I hope, this would be helpful..😊

You're after the UPDATE FROM syntax.

UPDATE 
  table T1  
SET 
  column1 = T2.column1 
FROM 
  table T2 
  INNER JOIN table T3 USING (column2) 
WHERE 
  T1.column2 = T2.column2;

References

• Code sample here: GROUP BY in UPDATE FROM clause
• And here
• Formal Syntax Specification