'\" t
.\"     Title: MERGE
.\"    Author: The PostgreSQL Global Development Group
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 2025
.\"    Manual: PostgreSQL 18.0 Documentation
.\"    Source: PostgreSQL 18.0
.\"  Language: English
.\"
.TH "MERGE" "7" "2025" "PostgreSQL 18.0" "PostgreSQL 18.0 Documentation"
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.SH "NAME"
MERGE \- conditionally insert, update, or delete rows of a table
.SH "SYNOPSIS"
.sp
.nf
[ WITH \fIwith_query\fR [, \&.\&.\&.] ]
MERGE INTO [ ONLY ] \fItarget_table_name\fR [ * ] [ [ AS ] \fItarget_alias\fR ]
    USING \fIdata_source\fR ON \fIjoin_condition\fR
    \fIwhen_clause\fR [\&.\&.\&.]
    [ RETURNING [ WITH ( { OLD | NEW } AS \fIoutput_alias\fR [, \&.\&.\&.] ) ]
                { * | \fIoutput_expression\fR [ [ AS ] \fIoutput_name\fR ] } [, \&.\&.\&.] ]

where \fIdata_source\fR is:

    { [ ONLY ] \fIsource_table_name\fR [ * ] | ( \fIsource_query\fR ) } [ [ AS ] \fIsource_alias\fR ]

and \fIwhen_clause\fR is:

    { WHEN MATCHED [ AND \fIcondition\fR ] THEN { \fImerge_update\fR | \fImerge_delete\fR | DO NOTHING } |
      WHEN NOT MATCHED BY SOURCE [ AND \fIcondition\fR ] THEN { \fImerge_update\fR | \fImerge_delete\fR | DO NOTHING } |
      WHEN NOT MATCHED [ BY TARGET ] [ AND \fIcondition\fR ] THEN { \fImerge_insert\fR | DO NOTHING } }

and \fImerge_insert\fR is:

    INSERT [( \fIcolumn_name\fR [, \&.\&.\&.] )]
        [ OVERRIDING { SYSTEM | USER } VALUE ]
        { VALUES ( { \fIexpression\fR | DEFAULT } [, \&.\&.\&.] ) | DEFAULT VALUES }

and \fImerge_update\fR is:

    UPDATE SET { \fIcolumn_name\fR = { \fIexpression\fR | DEFAULT } |
                 ( \fIcolumn_name\fR [, \&.\&.\&.] ) = [ ROW ] ( { \fIexpression\fR | DEFAULT } [, \&.\&.\&.] ) |
                 ( \fIcolumn_name\fR [, \&.\&.\&.] ) = ( \fIsub\-SELECT\fR )
               } [, \&.\&.\&.]

and \fImerge_delete\fR is:

    DELETE
.fi
.SH "DESCRIPTION"
.PP
\fBMERGE\fR
performs actions that modify rows in the target table identified as
\fItarget_table_name\fR, using the
\fIdata_source\fR\&.
\fBMERGE\fR
provides a single
SQL
statement that can conditionally
\fBINSERT\fR,
\fBUPDATE\fR
or
\fBDELETE\fR
rows, a task that would otherwise require multiple procedural language statements\&.
.PP
First, the
\fBMERGE\fR
command performs a join from
\fIdata_source\fR
to the target table producing zero or more candidate change rows\&. For each candidate change row, the status of
MATCHED,
NOT MATCHED BY SOURCE, or
NOT MATCHED [BY TARGET]
is set just once, after which
WHEN
clauses are evaluated in the order specified\&. For each candidate change row, the first clause to evaluate as true is executed\&. No more than one
WHEN
clause is executed for any candidate change row\&.
.PP
\fBMERGE\fR
actions have the same effect as regular
\fBUPDATE\fR,
\fBINSERT\fR, or
\fBDELETE\fR
commands of the same names\&. The syntax of those commands is different, notably that there is no
WHERE
clause and no table name is specified\&. All actions refer to the target table, though modifications to other tables may be made using triggers\&.
.PP
When
DO NOTHING
is specified, the source row is skipped\&. Since actions are evaluated in their specified order,
DO NOTHING
can be handy to skip non\-interesting source rows before more fine\-grained handling\&.
.PP
The optional
RETURNING
clause causes
\fBMERGE\fR
to compute and return value(s) based on each row inserted, updated, or deleted\&. Any expression using the source or target table\*(Aqs columns, or the
\fBmerge_action()\fR
function can be computed\&. By default, when an
\fBINSERT\fR
or
\fBUPDATE\fR
action is performed, the new values of the target table\*(Aqs columns are used, and when a
\fBDELETE\fR
is performed, the old values of the target table\*(Aqs columns are used, but it is also possible to explicitly request old and new values\&. The syntax of the
RETURNING
list is identical to that of the output list of
\fBSELECT\fR\&.
.PP
There is no separate
MERGE
privilege\&. If you specify an update action, you must have the
UPDATE
privilege on the column(s) of the target table that are referred to in the
SET
clause\&. If you specify an insert action, you must have the
INSERT
privilege on the target table\&. If you specify a delete action, you must have the
DELETE
privilege on the target table\&. If you specify a
DO NOTHING
action, you must have the
SELECT
privilege on at least one column of the target table\&. You will also need
SELECT
privilege on any column(s) of the
\fIdata_source\fR
and of the target table referred to in any
condition
(including
join_condition) or
expression\&. Privileges are tested once at statement start and are checked whether or not particular
WHEN
clauses are executed\&.
.PP
\fBMERGE\fR
is not supported if the target table is a materialized view, foreign table, or if it has any rules defined on it\&.
.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
\fBMERGE\fR
query\&. See
Section\ \&7.8
and
\fBSELECT\fR(7)
for details\&. Note that
WITH RECURSIVE
is not supported by
\fBMERGE\fR\&.
.RE
.PP
\fItarget_table_name\fR
.RS 4
The name (optionally schema\-qualified) of the target table or view to merge into\&. If
ONLY
is specified before a table name, matching rows are updated or deleted in the named table only\&. If
ONLY
is not specified, matching rows are also updated or deleted in any tables inheriting from the named table\&. Optionally,
*
can be specified after the table name to explicitly indicate that descendant tables are included\&. The
ONLY
keyword and
*
option do not affect insert actions, which always insert into the named table only\&.
.sp
If
\fItarget_table_name\fR
is a view, it must either be automatically updatable with no
INSTEAD OF
triggers, or it must have
INSTEAD OF
triggers for every type of action (INSERT,
UPDATE, and
DELETE) specified in the
WHEN
clauses\&. Views with rules are not supported\&.
.RE
.PP
\fItarget_alias\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
MERGE INTO foo AS f, the remainder of the
\fBMERGE\fR
statement must refer to this table as
f
not
foo\&.
.RE
.PP
\fIsource_table_name\fR
.RS 4
The name (optionally schema\-qualified) of the source table, view, or transition table\&. If
ONLY
is specified before the table name, matching rows are included from the named table only\&. If
ONLY
is not specified, matching rows are also included from 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
\fIsource_query\fR
.RS 4
A query (\fBSELECT\fR
statement or
\fBVALUES\fR
statement) that supplies the rows to be merged into the target table\&. Refer to the
\fBSELECT\fR(7)
statement or
\fBVALUES\fR(7)
statement for a description of the syntax\&.
.RE
.PP
\fIsource_alias\fR
.RS 4
A substitute name for the data source\&. When an alias is provided, it completely hides the actual name of the table or the fact that a query was issued\&.
.RE
.PP
\fIjoin_condition\fR
.RS 4
\fIjoin_condition\fR
is an expression resulting in a value of type
boolean
(similar to a
WHERE
clause) that specifies which rows in the
\fIdata_source\fR
match rows in the target table\&.
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBWarning\fR
.ps -1
.br
Only columns from the target table that attempt to match
\fIdata_source\fR
rows should appear in
\fIjoin_condition\fR\&.
\fIjoin_condition\fR
subexpressions that only reference the target table\*(Aqs columns can affect which action is taken, often in surprising ways\&.
.sp
If both
WHEN NOT MATCHED BY SOURCE
and
WHEN NOT MATCHED [BY TARGET]
clauses are specified, the
\fBMERGE\fR
command will perform a
FULL
join between
\fIdata_source\fR
and the target table\&. For this to work, at least one
\fIjoin_condition\fR
subexpression must use an operator that can support a hash join, or all of the subexpressions must use operators that can support a merge join\&.
.sp .5v
.RE
.RE
.PP
\fIwhen_clause\fR
.RS 4
At least one
WHEN
clause is required\&.
.sp
The
WHEN
clause may specify
WHEN MATCHED,
WHEN NOT MATCHED BY SOURCE, or
WHEN NOT MATCHED [BY TARGET]\&. Note that the
SQL
standard only defines
WHEN MATCHED
and
WHEN NOT MATCHED
(which is defined to mean no matching target row)\&.
WHEN NOT MATCHED BY SOURCE
is an extension to the
SQL
standard, as is the option to append
BY TARGET
to
WHEN NOT MATCHED, to make its meaning more explicit\&.
.sp
If the
WHEN
clause specifies
WHEN MATCHED
and the candidate change row matches a row in the
\fIdata_source\fR
to a row in the target table, the
WHEN
clause is executed if the
\fIcondition\fR
is absent or it evaluates to
true\&.
.sp
If the
WHEN
clause specifies
WHEN NOT MATCHED BY SOURCE
and the candidate change row represents a row in the target table that does not match a row in the
\fIdata_source\fR, the
WHEN
clause is executed if the
\fIcondition\fR
is absent or it evaluates to
true\&.
.sp
If the
WHEN
clause specifies
WHEN NOT MATCHED [BY TARGET]
and the candidate change row represents a row in the
\fIdata_source\fR
that does not match a row in the target table, the
WHEN
clause is executed if the
\fIcondition\fR
is absent or it evaluates to
true\&.
.RE
.PP
\fIcondition\fR
.RS 4
An expression that returns a value of type
boolean\&. If this expression for a
WHEN
clause returns
true, then the action for that clause is executed for that row\&.
.sp
A condition on a
WHEN MATCHED
clause can refer to columns in both the source and the target relations\&. A condition on a
WHEN NOT MATCHED BY SOURCE
clause can only refer to columns from the target relation, since by definition there is no matching source row\&. A condition on a
WHEN NOT MATCHED [BY TARGET]
clause can only refer to columns from the source relation, since by definition there is no matching target row\&. Only the system attributes from the target table are accessible\&.
.RE
.PP
\fImerge_insert\fR
.RS 4
The specification of an
INSERT
action that inserts one row into the target table\&. The target column names can be listed in any order\&. If no list of column names is given at all, the default is all the columns of the table in their declared order\&.
.sp
Each column not present in the explicit or implicit column list will be filled with a default value, either its declared default value or null if there is none\&.
.sp
If the target table is a partitioned table, each row is routed to the appropriate partition and inserted into it\&. If the target table is a partition, an error will occur if any input row violates the partition constraint\&.
.sp
Column names may not be specified more than once\&.
\fBINSERT\fR
actions cannot contain sub\-selects\&.
.sp
Only one
VALUES
clause can be specified\&. The
VALUES
clause can only refer to columns from the source relation, since by definition there is no matching target row\&.
.RE
.PP
\fImerge_update\fR
.RS 4
The specification of an
UPDATE
action that updates the current row of the target table\&. Column names may not be specified more than once\&.
.sp
Neither a table name nor a
WHERE
clause are allowed\&.
.RE
.PP
\fImerge_delete\fR
.RS 4
Specifies a
DELETE
action that deletes the current row of the target table\&. Do not include the table name or any other clauses, as you would normally do with a
\fBDELETE\fR(7)
command\&.
.RE
.PP
\fIcolumn_name\fR
.RS 4
The name of a column in the target table\&. The column name can be qualified with a subfield name or array subscript, if needed\&. (Inserting into only some fields of a composite column leaves the other fields null\&.) Do not include the table\*(Aqs name in the specification of a target column\&.
.RE
.PP
OVERRIDING SYSTEM VALUE
.RS 4
Without this clause, it is an error to specify an explicit value (other than
DEFAULT) for an identity column defined as
GENERATED ALWAYS\&. This clause overrides that restriction\&.
.RE
.PP
OVERRIDING USER VALUE
.RS 4
If this clause is specified, then any values supplied for identity columns defined as
GENERATED BY DEFAULT
are ignored and the default sequence\-generated values are applied\&.
.RE
.PP
DEFAULT VALUES
.RS 4
All columns will be filled with their default values\&. (An
OVERRIDING
clause is not permitted in this form\&.)
.RE
.PP
\fIexpression\fR
.RS 4
An expression to assign to the column\&. If used in a
WHEN MATCHED
clause, the expression can use values from the original row in the target table, and values from the
\fIdata_source\fR
row\&. If used in a
WHEN NOT MATCHED BY SOURCE
clause, the expression can only use values from the original row in the target table\&. If used in a
WHEN NOT MATCHED [BY TARGET]
clause, the expression can only use values from the
\fIdata_source\fR
row\&.
.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)\&.
.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\&. If used in a
WHEN MATCHED
clause, the sub\-query can refer to values from the original row in the target table, and values from the
\fIdata_source\fR
row\&. If used in a
WHEN NOT MATCHED BY SOURCE
clause, the sub\-query can only refer to values from the original row in the target table\&.
.RE
.PP
\fIoutput_alias\fR
.RS 4
An optional substitute name for
OLD
or
NEW
rows in the
RETURNING
list\&.
.sp
By default, old values from the target table can be returned by writing
OLD\&.\fIcolumn_name\fR
or
OLD\&.*, and new values can be returned by writing
NEW\&.\fIcolumn_name\fR
or
NEW\&.*\&. When an alias is provided, these names are hidden and the old or new rows must be referred to using the alias\&. For example
RETURNING WITH (OLD AS o, NEW AS n) o\&.*, n\&.*\&.
.RE
.PP
\fIoutput_expression\fR
.RS 4
An expression to be computed and returned by the
\fBMERGE\fR
command after each row is changed (whether inserted, updated, or deleted)\&. The expression can use any columns of the source or target tables, or the
\fBmerge_action()\fR
function to return additional information about the action executed\&.
.sp
Writing
*
will return all columns from the source table, followed by all columns from the target table\&. Often this will lead to a lot of duplication, since it is common for the source and target tables to have a lot of the same columns\&. This can be avoided by qualifying the
*
with the name or alias of the source or target table\&.
.sp
A column name or
*
may also be qualified using
OLD
or
NEW, or the corresponding
\fIoutput_alias\fR
for
OLD
or
NEW, to cause old or new values from the target table to be returned\&. An unqualified column name from the target table, or a column name or
*
qualified using the target table name or alias will return new values for
INSERT
and
UPDATE
actions, and old values for
DELETE
actions\&.
.RE
.PP
\fIoutput_name\fR
.RS 4
A name to use for a returned column\&.
.RE
.SH "OUTPUTS"
.PP
On successful completion, a
\fBMERGE\fR
command returns a command tag of the form
.sp
.if n \{\
.RS 4
.\}
.nf
MERGE \fItotal_count\fR
.fi
.if n \{\
.RE
.\}
.sp
The
\fItotal_count\fR
is the total number of rows changed (whether inserted, updated, or deleted)\&. If
\fItotal_count\fR
is 0, no rows were changed in any way\&.
.PP
If the
\fBMERGE\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) inserted, updated, or deleted by the command\&.
.SH "NOTES"
.PP
The following steps take place during the execution of
\fBMERGE\fR\&.
.sp
.RS 4
.ie n \{\
\h'-04' 1.\h'+01'\c
.\}
.el \{\
.sp -1
.IP "  1." 4.2
.\}
Perform any
BEFORE STATEMENT
triggers for all actions specified, whether or not their
WHEN
clauses match\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04' 2.\h'+01'\c
.\}
.el \{\
.sp -1
.IP "  2." 4.2
.\}
Perform a join from source to target table\&. The resulting query will be optimized normally and will produce a set of candidate change rows\&. For each candidate change row,
.sp
.RS 4
.ie n \{\
\h'-04' 1.\h'+01'\c
.\}
.el \{\
.sp -1
.IP "  1." 4.2
.\}
Evaluate whether each row is
MATCHED,
NOT MATCHED BY SOURCE, or
NOT MATCHED [BY TARGET]\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04' 2.\h'+01'\c
.\}
.el \{\
.sp -1
.IP "  2." 4.2
.\}
Test each
WHEN
condition in the order specified until one returns true\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04' 3.\h'+01'\c
.\}
.el \{\
.sp -1
.IP "  3." 4.2
.\}
When a condition returns true, perform the following actions:
.sp
.RS 4
.ie n \{\
\h'-04' 1.\h'+01'\c
.\}
.el \{\
.sp -1
.IP "  1." 4.2
.\}
Perform any
BEFORE ROW
triggers that fire for the action\*(Aqs event type\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04' 2.\h'+01'\c
.\}
.el \{\
.sp -1
.IP "  2." 4.2
.\}
Perform the specified action, invoking any check constraints on the target table\&.
.RE
.sp
.RS 4
.ie n \{\
\h'-04' 3.\h'+01'\c
.\}
.el \{\
.sp -1
.IP "  3." 4.2
.\}
Perform any
AFTER ROW
triggers that fire for the action\*(Aqs event type\&.
.RE
.sp
If the target relation is a view with
INSTEAD OF ROW
triggers for the action\*(Aqs event type, they are used to perform the action instead\&.
.RE
.RE
.sp
.RS 4
.ie n \{\
\h'-04' 3.\h'+01'\c
.\}
.el \{\
.sp -1
.IP "  3." 4.2
.\}
Perform any
AFTER STATEMENT
triggers for actions specified, whether or not they actually occur\&. This is similar to the behavior of an
\fBUPDATE\fR
statement that modifies no rows\&.
.RE
.sp
In summary, statement triggers for an event type (say,
\fBINSERT\fR) will be fired whenever we
\fIspecify\fR
an action of that kind\&. In contrast, row\-level triggers will fire only for the specific event type being
\fIexecuted\fR\&. So a
\fBMERGE\fR
command might fire statement triggers for both
\fBUPDATE\fR
and
\fBINSERT\fR, even though only
\fBUPDATE\fR
row triggers were fired\&.
.PP
You should ensure that the join produces at most one candidate change row for each target row\&. In other words, a target row shouldn\*(Aqt join to more than one data source row\&. If it does, then only one of the candidate change rows will be used to modify the target row; later attempts to modify the row will cause an error\&. This can also occur if row triggers make changes to the target table and the rows so modified are then subsequently also modified by
\fBMERGE\fR\&. If the repeated action is an
\fBINSERT\fR, this will cause a uniqueness violation, while a repeated
\fBUPDATE\fR
or
\fBDELETE\fR
will cause a cardinality violation; the latter behavior is required by the
SQL
standard\&. This differs from historical
PostgreSQL
behavior of joins in
\fBUPDATE\fR
and
\fBDELETE\fR
statements where second and subsequent attempts to modify the same row are simply ignored\&.
.PP
If a
WHEN
clause omits an
AND
sub\-clause, it becomes the final reachable clause of that kind (MATCHED,
NOT MATCHED BY SOURCE, or
NOT MATCHED [BY TARGET])\&. If a later
WHEN
clause of that kind is specified it would be provably unreachable and an error is raised\&. If no final reachable clause is specified of either kind, it is possible that no action will be taken for a candidate change row\&.
.PP
The order in which rows are generated from the data source is indeterminate by default\&. A
\fIsource_query\fR
can be used to specify a consistent ordering, if required, which might be needed to avoid deadlocks between concurrent transactions\&.
.PP
When
\fBMERGE\fR
is run concurrently with other commands that modify the target table, the usual transaction isolation rules apply; see
Section\ \&13.2
for an explanation on the behavior at each isolation level\&. You may also wish to consider using
\fBINSERT \&.\&.\&. ON CONFLICT\fR
as an alternative statement which offers the ability to run an
\fBUPDATE\fR
if a concurrent
\fBINSERT\fR
occurs\&. There are a variety of differences and restrictions between the two statement types and they are not interchangeable\&.
.SH "EXAMPLES"
.PP
Perform maintenance on
customer_accounts
based upon new
recent_transactions\&.
.sp
.if n \{\
.RS 4
.\}
.nf
MERGE INTO customer_account ca
USING recent_transactions t
ON t\&.customer_id = ca\&.customer_id
WHEN MATCHED THEN
  UPDATE SET balance = balance + transaction_value
WHEN NOT MATCHED THEN
  INSERT (customer_id, balance)
  VALUES (t\&.customer_id, t\&.transaction_value);
.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\&. Don\*(Aqt allow entries that have zero stock\&. Return details of all changes made\&.
.sp
.if n \{\
.RS 4
.\}
.nf
MERGE INTO wines w
USING wine_stock_changes s
ON s\&.winename = w\&.winename
WHEN NOT MATCHED AND s\&.stock_delta > 0 THEN
  INSERT VALUES(s\&.winename, s\&.stock_delta)
WHEN MATCHED AND w\&.stock + s\&.stock_delta > 0 THEN
  UPDATE SET stock = w\&.stock + s\&.stock_delta
WHEN MATCHED THEN
  DELETE
RETURNING merge_action(), w\&.winename, old\&.stock AS old_stock, new\&.stock AS new_stock;
.fi
.if n \{\
.RE
.\}
.sp
The
wine_stock_changes
table might be, for example, a temporary table recently loaded into the database\&.
.PP
Update
wines
based on a replacement wine list, inserting rows for any new stock, updating modified stock entries, and deleting any wines not present in the new list\&.
.sp
.if n \{\
.RS 4
.\}
.nf
MERGE INTO wines w
USING new_wine_list s
ON s\&.winename = w\&.winename
WHEN NOT MATCHED BY TARGET THEN
  INSERT VALUES(s\&.winename, s\&.stock)
WHEN MATCHED AND w\&.stock != s\&.stock THEN
  UPDATE SET stock = s\&.stock
WHEN NOT MATCHED BY SOURCE THEN
  DELETE;
.fi
.if n \{\
.RE
.\}
.sp
.SH "COMPATIBILITY"
.PP
This command conforms to the
SQL
standard\&.
.PP
The
WITH
clause,
BY SOURCE
and
BY TARGET
qualifiers to
WHEN NOT MATCHED,
DO NOTHING
action, and
RETURNING
clause are extensions to the
SQL
standard\&.