path: root/doc/src/sgml/man7/UPDATE.7

'\" t
.\"     Title: UPDATE
.\"    Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 2023
.\"    Manual: PostgreSQL 15.4 Documentation
.\"    Source: PostgreSQL 15.4
.\"  Language: English
.\"
.TH "UPDATE" "7" "2023" "PostgreSQL 15.4" "PostgreSQL 15.4 Documentation"
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.SH "NAME"
UPDATE \- update rows of a table
.SH "SYNOPSIS"
.sp
.nf
[ WITH [ RECURSIVE ] \fIwith_query\fR [, \&.\&.\&.] ]
UPDATE [ ONLY ] \fItable_name\fR [ * ] [ [ AS ] \fIalias\fR ]
    SET { \fIcolumn_name\fR = { \fIexpression\fR | DEFAULT } |
          ( \fIcolumn_name\fR [, \&.\&.\&.] ) = [ ROW ] ( { \fIexpression\fR | DEFAULT } [, \&.\&.\&.] ) |
          ( \fIcolumn_name\fR [, \&.\&.\&.] ) = ( \fIsub\-SELECT\fR )
        } [, \&.\&.\&.]
    [ FROM \fIfrom_item\fR [, \&.\&.\&.] ]
    [ WHERE \fIcondition\fR | WHERE CURRENT OF \fIcursor_name\fR ]
    [ RETURNING * | \fIoutput_expression\fR [ [ AS ] \fIoutput_name\fR ] [, \&.\&.\&.] ]
.fi
.SH "DESCRIPTION"
.PP
\fBUPDATE\fR
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\&.
.PP
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\&.
.PP
The optional
RETURNING
clause causes
\fBUPDATE\fR
to compute and return value(s) based on each row actually updated\&. Any expression using the table\*(Aqs columns, and/or columns of other tables mentioned in
FROM, can be computed\&. The new (post\-update) values of the table\*(Aqs columns are used\&. The syntax of the
RETURNING
list is identical to that of the output list of
\fBSELECT\fR\&.
.PP
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
\fIexpressions\fR
or
\fIcondition\fR\&.
.SH "PARAMETERS"
.PP
\fIwith_query\fR
.RS 4
The
WITH
clause allows you to specify one or more subqueries that can be referenced by name in the
\fBUPDATE\fR
query\&. See
Section\ \&7.8
and
\fBSELECT\fR(7)
for details\&.
.RE
.PP
\fItable_name\fR
.RS 4
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\&.
.RE
.PP
\fIalias\fR
.RS 4
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
\fBUPDATE\fR
statement must refer to this table as
f
not
foo\&.
.RE
.PP
\fIcolumn_name\fR
.RS 4
The name of a column in the table named by
\fItable_name\fR\&. The column name can be qualified with a subfield name or array subscript, if needed\&. Do not include the table\*(Aqs name in the specification of a target column \(em for example,
UPDATE table_name SET table_name\&.col = 1
is invalid\&.
.RE
.PP
\fIexpression\fR
.RS 4
An expression to assign to the column\&. The expression can use the old values of this and other columns in the table\&.
.RE
.PP
DEFAULT
.RS 4
Set the column to its default value (which will be NULL if no specific default expression has been assigned to it)\&. An identity column will be set to a new value generated by the associated sequence\&. For a generated column, specifying this is permitted but merely specifies the normal behavior of computing the column from its generation expression\&.
.RE
.PP
\fIsub\-SELECT\fR
.RS 4
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\&.
.RE
.PP
\fIfrom_item\fR
.RS 4
A table expression allowing columns from other tables to appear in the
WHERE
condition and update expressions\&. This uses the same syntax as the
FROM
clause of a
\fBSELECT\fR
statement; for example, an alias for the table name can be specified\&. Do not repeat the target table as a
\fIfrom_item\fR
unless you intend a self\-join (in which case it must appear with an alias in the
\fIfrom_item\fR)\&.
.RE
.PP
\fIcondition\fR
.RS 4
An expression that returns a value of type
boolean\&. Only rows for which this expression returns
true
will be updated\&.
.RE
.PP
\fIcursor_name\fR
.RS 4
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
\fBUPDATE\fR\*(Aqs target table\&. Note that
WHERE CURRENT OF
cannot be specified together with a Boolean condition\&. See
\fBDECLARE\fR(7)
for more information about using cursors with
WHERE CURRENT OF\&.
.RE
.PP
\fIoutput_expression\fR
.RS 4
An expression to be computed and returned by the
\fBUPDATE\fR
command after each row is updated\&. The expression can use any column names of the table named by
\fItable_name\fR
or table(s) listed in
FROM\&. Write
*
to return all columns\&.
.RE
.PP
\fIoutput_name\fR
.RS 4
A name to use for a returned column\&.
.RE
.SH "OUTPUTS"
.PP
On successful completion, an
\fBUPDATE\fR
command returns a command tag of the form
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE \fIcount\fR
.fi
.if n \{\
.RE
.\}
.sp
The
\fIcount\fR
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
\fIcondition\fR
when updates were suppressed by a
BEFORE UPDATE
trigger\&. If
\fIcount\fR
is 0, no rows were updated by the query (this is not considered an error)\&.
.PP
If the
\fBUPDATE\fR
command contains a
RETURNING
clause, the result will be similar to that of a
\fBSELECT\fR
statement containing the columns and values defined in the
RETURNING
list, computed over the row(s) updated by the command\&.
.SH "NOTES"
.PP
When a
FROM
clause is present, what essentially happens is that the target table is joined to the tables mentioned in the
\fIfrom_item\fR
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\*(Aqt 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\&.
.PP
Because of this indeterminacy, referencing other tables only within sub\-selects is safer, though often harder to read and slower than using a join\&.
.PP
In the case of a partitioned table, updating a row might cause it to no longer satisfy the partition constraint of the containing partition\&. In that case, if there is some other partition in the partition tree for which this row satisfies its partition constraint, then the row is moved to that partition\&. If there is no such partition, an error will occur\&. Behind the scenes, the row movement is actually a
\fBDELETE\fR
and
\fBINSERT\fR
operation\&.
.PP
There is a possibility that a concurrent
\fBUPDATE\fR
or
\fBDELETE\fR
on the row being moved will get a serialization failure error\&. Suppose session 1 is performing an
\fBUPDATE\fR
on a partition key, and meanwhile a concurrent session 2 for which this row is visible performs an
\fBUPDATE\fR
or
\fBDELETE\fR
operation on this row\&. In such case, session 2\*(Aqs
\fBUPDATE\fR
or
\fBDELETE\fR
will detect the row movement and raise a serialization failure error (which always returns with an SQLSTATE code \*(Aq40001\*(Aq)\&. Applications may wish to retry the transaction if this occurs\&. In the usual case where the table is not partitioned, or where there is no row movement, session 2 would have identified the newly updated row and carried out the
\fBUPDATE\fR/\fBDELETE\fR
on this new row version\&.
.PP
Note that while rows can be moved from local partitions to a foreign\-table partition (provided the foreign data wrapper supports tuple routing), they cannot be moved from a foreign\-table partition to another partition\&.
.PP
An attempt of moving a row from one partition to another will fail if a foreign key is found to directly reference an ancestor of the source partition that is not the same as the ancestor that\*(Aqs mentioned in the
\fBUPDATE\fR
query\&.
.SH "EXAMPLES"
.PP
Change the word
Drama
to
Dramatic
in the column
kind
of the table
films:
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE films SET kind = \*(AqDramatic\*(Aq WHERE kind = \*(AqDrama\*(Aq;
.fi
.if n \{\
.RE
.\}
.PP
Adjust temperature entries and reset precipitation to its default value in one row of the table
weather:
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
  WHERE city = \*(AqSan Francisco\*(Aq AND date = \*(Aq2003\-07\-03\*(Aq;
.fi
.if n \{\
.RE
.\}
.PP
Perform the same operation and return the updated entries:
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
  WHERE city = \*(AqSan Francisco\*(Aq AND date = \*(Aq2003\-07\-03\*(Aq
  RETURNING temp_lo, temp_hi, prcp;
.fi
.if n \{\
.RE
.\}
.PP
Use the alternative column\-list syntax to do the same update:
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE weather SET (temp_lo, temp_hi, prcp) = (temp_lo+1, temp_lo+15, DEFAULT)
  WHERE city = \*(AqSan Francisco\*(Aq AND date = \*(Aq2003\-07\-03\*(Aq;
.fi
.if n \{\
.RE
.\}
.PP
Increment the sales count of the salesperson who manages the account for Acme Corporation, using the
FROM
clause syntax:
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE employees SET sales_count = sales_count + 1 FROM accounts
  WHERE accounts\&.name = \*(AqAcme Corporation\*(Aq
  AND employees\&.id = accounts\&.sales_person;
.fi
.if n \{\
.RE
.\}
.PP
Perform the same operation, using a sub\-select in the
WHERE
clause:
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE employees SET sales_count = sales_count + 1 WHERE id =
  (SELECT sales_person FROM accounts WHERE name = \*(AqAcme Corporation\*(Aq);
.fi
.if n \{\
.RE
.\}
.PP
Update contact names in an accounts table to match the currently assigned salespeople:
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE accounts SET (contact_first_name, contact_last_name) =
    (SELECT first_name, last_name FROM employees
     WHERE employees\&.id = accounts\&.sales_person);
.fi
.if n \{\
.RE
.\}
.sp
A similar result could be accomplished with a join:
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE accounts SET contact_first_name = first_name,
                    contact_last_name = last_name
  FROM employees WHERE employees\&.id = accounts\&.sales_person;
.fi
.if n \{\
.RE
.\}
.sp
However, the second query may give unexpected results if
employees\&.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_person
entry, the first query will set the corresponding name fields to NULL, whereas the second query will not update that row at all\&.
.PP
Update statistics in a summary table to match the current data:
.sp
.if n \{\
.RS 4
.\}
.nf
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);
.fi
.if n \{\
.RE
.\}
.PP
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:
.sp
.if n \{\
.RS 4
.\}
.nf
BEGIN;
\-\- other operations
SAVEPOINT sp1;
INSERT INTO wines VALUES(\*(AqChateau Lafite 2003\*(Aq, \*(Aq24\*(Aq);
\-\- 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 = \*(AqChateau Lafite 2003\*(Aq;
\-\- continue with other operations, and eventually
COMMIT;
.fi
.if n \{\
.RE
.\}
.PP
Change the
kind
column of the table
films
in the row on which the cursor
c_films
is currently positioned:
.sp
.if n \{\
.RS 4
.\}
.nf
UPDATE films SET kind = \*(AqDramatic\*(Aq WHERE CURRENT OF c_films;
.fi
.if n \{\
.RE
.\}
.SH "COMPATIBILITY"
.PP
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
\fBUPDATE\fR\&.
.PP
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\&.
.PP
According to the standard, the source value for a parenthesized sub\-list of target column names can be any row\-valued expression yielding the correct number of columns\&.
PostgreSQL
only allows the source value to be a
row constructor
or a sub\-SELECT\&. An individual column\*(Aqs updated value can be specified as
DEFAULT
in the row\-constructor case, but not inside a sub\-SELECT\&.