The question is old but I felt the best answer hadn't been given, yet.
Is there an
UPDATEsyntax ... without specifying the column names?
You don't need to know any column names except for some unique column(s) to join on (id in the example). Works reliably for any possible corner case I can think of.
This is specific to PostgreSQL. I am building dynamic code based on the the information_schema, in particular the table information_schema.columns, which is defined in the SQL standard and most major RDBMS (except Oracle) have it. But a DO statement with PL/pgSQL code executing dynamic SQL is totally non-standard PostgreSQL syntax.
DO
$do$
BEGIN
EXECUTE (
SELECT
'UPDATE b
SET (' || string_agg( quote_ident(column_name), ',') || ')
= (' || string_agg('a.' || quote_ident(column_name), ',') || ')
FROM a
WHERE b.id = 123
AND a.id = b.id'
FROM information_schema.columns
WHERE table_name = 'a' -- table name, case sensitive
AND table_schema = 'public' -- schema name, case sensitive
AND column_name <> 'id' -- all columns except id
);
END
$do$;
Assuming a matching column in b for every column in a, but not the other way round. b can have additional columns.
WHERE b.id = 123 is optional, to update a selected row.
Related answers with more explanation:
You still need to know the list of column names that both tables share. With a syntax shortcut for updating multiple columns - shorter than what other answers suggested so far in any case.
UPDATE b
SET ( column1, column2, column3)
= (a.column1, a.column2, a.column3)
FROM a
WHERE b.id = 123 -- optional, to update only selected row
AND a.id = b.id;
This syntax was introduced with Postgres 8.2 in 2006, long before the question was asked. Details in the manual.
Related:
BIf all columns of A are defined NOT NULL (but not necessarily B),
and you know the column names of B (but not necessarily A).
UPDATE b
SET (column1, column2, column3, column4)
= (COALESCE(ab.column1, b.column1)
, COALESCE(ab.column2, b.column2)
, COALESCE(ab.column3, b.column3)
, COALESCE(ab.column4, b.column4)
)
FROM (
SELECT *
FROM a
NATURAL LEFT JOIN b -- append missing columns
WHERE b.id IS NULL -- only if anything actually changes
AND a.id = 123 -- optional, to update only selected row
) ab
WHERE b.id = ab.id;
The NATURAL LEFT JOIN joins a row from b where all columns of the same name hold same values. We don't need an update in this case (nothing changes) and can eliminate those rows early in the process (WHERE b.id IS NULL).
We still need to find a matching row, so b.id = ab.id in the outer query.
db<>fiddle here
Old sqlfiddle.
This is standard SQL except for the FROM clause.
It works no matter which of the columns are actually present in A, but the query cannot distinguish between actual NULL values and missing columns in A, so it is only reliable if all columns in A are defined NOT NULL.
There are multiple possible variations, depending on what you know about both tables.