UPDATE(7)
NAME
UPDATE - update rows of a table
SYNOPSIS
[ WITH [ RECURSIVE ] with_query [, ...] ]
UPDATE [ ONLY ] table_name [ * ] [ [ AS ] alias ]
SET { column_name = { expression | DEFAULT } |
( column_name [, ...] ) = ( { expression | DEFAULT } [, ...] ) |
( column_name [, ...] ) = ( sub-SELECT )
} [, ...]
[ FROM from_list ]
[ WHERE condition | WHERE CURRENT OF cursor_name ]
[ RETURNING * | output_expression [ [ AS ] output_name ] [, ...] ]
DESCRIPTION
UPDATE changes the values of the specified columns in all rows that satisfy the condition. Only the columns to be modified need be mentioned in the SET clause; columns not explicitly modified retain their previous values. There are two ways to modify a table using information contained in other tables in the database: using sub-selects, or specifying additional tables in the FROM clause. Which technique is more appropriate depends on the specific circumstances. The optional RETURNING clause causes UPDATE to compute and return value(s) based on each row actually updated. Any expression using the table's columns, and/or columns of other tables mentioned in FROM, can be computed. The new (post-update) values of the table's columns are used. The syntax of the RETURNING list is identical to that of the output list of SELECT. You must have the UPDATE privilege on the table, or at least on the column(s) that are listed to be updated. You must also have the SELECT privilege on any column whose values are read in the expressions or condition.
PARAMETERS
with_query
The WITH clause allows you to specify one or more subqueries that
can be referenced by name in the UPDATE query. See Section 7.8,
"WITH Queries (Common Table Expressions)", in the documentation and
SELECT(7) for details.
table_name
The name (optionally schema-qualified) of the table to update. If
ONLY is specified before the table name, matching rows are updated
in the named table only. If ONLY is not specified, matching rows
are also updated in any tables inheriting from the named table.
Optionally, * can be specified after the table name to explicitly
indicate that descendant tables are included.
alias
A substitute name for the target table. When an alias is provided,
it completely hides the actual name of the table. For example,
given UPDATE foo AS f, the remainder of the UPDATE statement must
refer to this table as f not foo.
column_name
The name of a column in the table named by table_name. The column
name can be qualified with a subfield name or array subscript, if
needed. Do not include the table's name in the specification of a
target column --- for example, UPDATE table_name SET table_name.col =
1 is invalid.
expression
An expression to assign to the column. The expression can use the
old values of this and other columns in the table.
DEFAULT
Set the column to its default value (which will be NULL if no
specific default expression has been assigned to it).
sub-SELECT
A SELECT sub-query that produces as many output columns as are
listed in the parenthesized column list preceding it. The sub-query
must yield no more than one row when executed. If it yields one
row, its column values are assigned to the target columns; if it
yields no rows, NULL values are assigned to the target columns. The
sub-query can refer to old values of the current row of the table
being updated.
from_list
A list of table expressions, allowing columns from other tables to
appear in the WHERE condition and the update expressions. This is
similar to the list of tables that can be specified in the FROM
Clause of a SELECT statement. Note that the target table must not
appear in the from_list, unless you intend a self-join (in which
case it must appear with an alias in the from_list).
condition
An expression that returns a value of type boolean. Only rows for
which this expression returns true will be updated.
cursor_name
The name of the cursor to use in a WHERE CURRENT OF condition. The
row to be updated is the one most recently fetched from this
cursor. The cursor must be a non-grouping query on the UPDATE's
target table. Note that WHERE CURRENT OF cannot be specified
together with a Boolean condition. See DECLARE(7) for more
information about using cursors with WHERE CURRENT OF.
output_expression
An expression to be computed and returned by the UPDATE command
after each row is updated. The expression can use any column names
of the table named by table_name or table(s) listed in FROM. Write
* to return all columns.
output_name
A name to use for a returned column.
OUTPUTS
On successful completion, an UPDATE command returns a command tag of
the form
UPDATE count
The count is the number of rows updated, including matched rows whose
values did not change. Note that the number may be less than the number
of rows that matched the condition when updates were suppressed by a
BEFORE UPDATE trigger. If count is 0, no rows were updated by the query
(this is not considered an error).
If the UPDATE command contains a RETURNING clause, the result will be
similar to that of a SELECT statement containing the columns and values
defined in the RETURNING list, computed over the row(s) updated by the
command.
NOTES
When a FROM clause is present, what essentially happens is that the target table is joined to the tables mentioned in the from_list, and each output row of the join represents an update operation for the target table. When using FROM you should ensure that the join produces at most one output row for each row to be modified. In other words, a target row shouldn't join to more than one row from the other table(s). If it does, then only one of the join rows will be used to update the target row, but which one will be used is not readily predictable. Because of this indeterminacy, referencing other tables only within sub-selects is safer, though often harder to read and slower than using a join.
EXAMPLES
Change the word Drama to Dramatic in the column kind of the table
films:
UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';
Adjust temperature entries and reset precipitation to its default value
in one row of the table weather:
UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
WHERE city = 'San Francisco' AND date = '2003-07-03';
Perform the same operation and return the updated entries:
UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
WHERE city = 'San Francisco' AND date = '2003-07-03'
RETURNING temp_lo, temp_hi, prcp;
Use the alternative column-list syntax to do the same update:
UPDATE weather SET (temp_lo, temp_hi, prcp) = (temp_lo+1, temp_lo+15, DEFAULT)
WHERE city = 'San Francisco' AND date = '2003-07-03';
Increment the sales count of the salesperson who manages the account
for Acme Corporation, using the FROM clause syntax:
UPDATE employees SET sales_count = sales_count + 1 FROM accounts
WHERE accounts.name = 'Acme Corporation'
AND employees.id = accounts.sales_person;
Perform the same operation, using a sub-select in the WHERE clause:
UPDATE employees SET sales_count = sales_count + 1 WHERE id =
(SELECT sales_person FROM accounts WHERE name = 'Acme Corporation');
Update contact names in an accounts table to match the currently
assigned salesmen:
UPDATE accounts SET (contact_first_name, contact_last_name) =
(SELECT first_name, last_name FROM salesmen
WHERE salesmen.id = accounts.sales_id);
A similar result could be accomplished with a join:
UPDATE accounts SET contact_first_name = first_name,
contact_last_name = last_name
FROM salesmen WHERE salesmen.id = accounts.sales_id;
However, the second query may give unexpected results if salesmen.id is
not a unique key, whereas the first query is guaranteed to raise an
error if there are multiple id matches. Also, if there is no match for
a particular accounts.sales_id entry, the first query will set the
corresponding name fields to NULL, whereas the second query will not
update that row at all.
Update statistics in a summary table to match the current data:
UPDATE summary s SET (sum_x, sum_y, avg_x, avg_y) =
(SELECT sum(x), sum(y), avg(x), avg(y) FROM data d
WHERE d.group_id = s.group_id);
Attempt to insert a new stock item along with the quantity of stock. If
the item already exists, instead update the stock count of the existing
item. To do this without failing the entire transaction, use
savepoints:
BEGIN;
-- other operations
SAVEPOINT sp1;
INSERT INTO wines VALUES('Chateau Lafite 2003', '24');
-- Assume the above fails because of a unique key violation,
-- so now we issue these commands:
ROLLBACK TO sp1;
UPDATE wines SET stock = stock + 24 WHERE winename = 'Chateau Lafite 2003';
-- continue with other operations, and eventually
COMMIT;
Change the kind column of the table films in the row on which the
cursor c_films is currently positioned:
UPDATE films SET kind = 'Dramatic' WHERE CURRENT OF c_films;
COMPATIBILITY
This command conforms to the SQL standard, except that the FROM and RETURNING clauses are PostgreSQL extensions, as is the ability to use WITH with UPDATE. Some other database systems offer a FROM option in which the target table is supposed to be listed again within FROM. That is not how PostgreSQL interprets FROM. Be careful when porting applications that use this extension. According to the standard, the source value for a parenthesized sub-list of column names can be any row-valued expression yielding the correct number of columns. PostgreSQL only allows the source value to be a parenthesized list of expressions (a row constructor) or a sub-SELECT. An individual column's updated value can be specified as DEFAULT in the row-constructor case, but not inside a sub-SELECT.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
