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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>MERGE</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="sql-lock.html" title="LOCK" /><link rel="next" href="sql-move.html" title="MOVE" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">MERGE</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="sql-lock.html" title="LOCK">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="sql-commands.html" title="SQL Commands">Up</a></td><th width="60%" align="center">SQL Commands</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 16.3 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="sql-move.html" title="MOVE">Next</a></td></tr></table><hr /></div><div class="refentry" id="SQL-MERGE"><div class="titlepage"></div><a id="id-1.9.3.156.1" class="indexterm"></a><div class="refnamediv"><h2><span class="refentrytitle">MERGE</span></h2><p>MERGE — conditionally insert, update, or delete rows of a table</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><pre class="synopsis">
[ WITH <em class="replaceable"><code>with_query</code></em> [, ...] ]
MERGE INTO [ ONLY ] <em class="replaceable"><code>target_table_name</code></em> [ * ] [ [ AS ] <em class="replaceable"><code>target_alias</code></em> ]
USING <em class="replaceable"><code>data_source</code></em> ON <em class="replaceable"><code>join_condition</code></em>
<em class="replaceable"><code>when_clause</code></em> [...]
<span class="phrase">where <em class="replaceable"><code>data_source</code></em> is:</span>
{ [ ONLY ] <em class="replaceable"><code>source_table_name</code></em> [ * ] | ( <em class="replaceable"><code>source_query</code></em> ) } [ [ AS ] <em class="replaceable"><code>source_alias</code></em> ]
<span class="phrase">and <em class="replaceable"><code>when_clause</code></em> is:</span>
{ WHEN MATCHED [ AND <em class="replaceable"><code>condition</code></em> ] THEN { <em class="replaceable"><code>merge_update</code></em> | <em class="replaceable"><code>merge_delete</code></em> | DO NOTHING } |
WHEN NOT MATCHED [ AND <em class="replaceable"><code>condition</code></em> ] THEN { <em class="replaceable"><code>merge_insert</code></em> | DO NOTHING } }
<span class="phrase">and <em class="replaceable"><code>merge_insert</code></em> is:</span>
INSERT [( <em class="replaceable"><code>column_name</code></em> [, ...] )]
[ OVERRIDING { SYSTEM | USER } VALUE ]
{ VALUES ( { <em class="replaceable"><code>expression</code></em> | DEFAULT } [, ...] ) | DEFAULT VALUES }
<span class="phrase">and <em class="replaceable"><code>merge_update</code></em> is:</span>
UPDATE SET { <em class="replaceable"><code>column_name</code></em> = { <em class="replaceable"><code>expression</code></em> | DEFAULT } |
( <em class="replaceable"><code>column_name</code></em> [, ...] ) = [ ROW ] ( { <em class="replaceable"><code>expression</code></em> | DEFAULT } [, ...] ) |
( <em class="replaceable"><code>column_name</code></em> [, ...] ) = ( <em class="replaceable"><code>sub-SELECT</code></em> )
} [, ...]
<span class="phrase">and <em class="replaceable"><code>merge_delete</code></em> is:</span>
DELETE
</pre></div><div class="refsect1" id="id-1.9.3.156.5"><h2>Description</h2><p>
<code class="command">MERGE</code> performs actions that modify rows in the
target table identified as <em class="replaceable"><code>target_table_name</code></em>,
using the <em class="replaceable"><code>data_source</code></em>.
<code class="command">MERGE</code> provides a single <acronym class="acronym">SQL</acronym>
statement that can conditionally <code class="command">INSERT</code>,
<code class="command">UPDATE</code> or <code class="command">DELETE</code> rows, a task
that would otherwise require multiple procedural language statements.
</p><p>
First, the <code class="command">MERGE</code> command performs a join
from <em class="replaceable"><code>data_source</code></em> to
the target table
producing zero or more candidate change rows. For each candidate change
row, the status of <code class="literal">MATCHED</code> or <code class="literal">NOT MATCHED</code>
is set just once, after which <code class="literal">WHEN</code> 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 <code class="literal">WHEN</code>
clause is executed for any candidate change row.
</p><p>
<code class="command">MERGE</code> actions have the same effect as
regular <code class="command">UPDATE</code>, <code class="command">INSERT</code>, or
<code class="command">DELETE</code> commands of the same names. The syntax of
those commands is different, notably that there is no <code class="literal">WHERE</code>
clause and no table name is specified. All actions refer to the
target table,
though modifications to other tables may be made using triggers.
</p><p>
When <code class="literal">DO NOTHING</code> is specified, the source row is
skipped. Since actions are evaluated in their specified order, <code class="literal">DO
NOTHING</code> can be handy to skip non-interesting source rows before
more fine-grained handling.
</p><p>
There is no separate <code class="literal">MERGE</code> privilege.
If you specify an update action, you must have the
<code class="literal">UPDATE</code> privilege on the column(s)
of the target table
that are referred to in the <code class="literal">SET</code> clause.
If you specify an insert action, you must have the <code class="literal">INSERT</code>
privilege on the target table.
If you specify a delete action, you must have the <code class="literal">DELETE</code>
privilege on the target table.
If you specify a <code class="literal">DO NOTHING</code> action, you must have
the <code class="literal">SELECT</code> privilege on at least one column
of the target table.
You will also need <code class="literal">SELECT</code> privilege on any column(s)
of the <em class="replaceable"><code>data_source</code></em> and
of the target table referred to
in any <code class="literal">condition</code> (including <code class="literal">join_condition</code>)
or <code class="literal">expression</code>.
Privileges are tested once at statement start and are checked
whether or not particular <code class="literal">WHEN</code> clauses are executed.
</p><p>
<code class="command">MERGE</code> is not supported if the
target table is a
materialized view, foreign table, or if it has any
rules defined on it.
</p></div><div class="refsect1" id="id-1.9.3.156.6"><h2>Parameters</h2><div class="variablelist"><dl class="variablelist"><dt><span class="term"><em class="replaceable"><code>with_query</code></em></span></dt><dd><p>
The <code class="literal">WITH</code> clause allows you to specify one or more
subqueries that can be referenced by name in the <code class="command">MERGE</code>
query. See <a class="xref" href="queries-with.html" title="7.8. WITH Queries (Common Table Expressions)">Section 7.8</a> and <a class="xref" href="sql-select.html" title="SELECT"><span class="refentrytitle">SELECT</span></a>
for details. Note that <code class="literal">WITH RECURSIVE</code> is not supported
by <code class="command">MERGE</code>.
</p></dd><dt><span class="term"><em class="replaceable"><code>target_table_name</code></em></span></dt><dd><p>
The name (optionally schema-qualified) of the target table to merge into.
If <code class="literal">ONLY</code> is specified before the table name, matching
rows are updated or deleted in the named table only. If
<code class="literal">ONLY</code> is not specified, matching rows are also updated
or deleted in any tables inheriting from the named table. Optionally,
<code class="literal">*</code> can be specified after the table name to explicitly
indicate that descendant tables are included. The
<code class="literal">ONLY</code> keyword and <code class="literal">*</code> option do not
affect insert actions, which always insert into the named table only.
</p></dd><dt><span class="term"><em class="replaceable"><code>target_alias</code></em></span></dt><dd><p>
A substitute name for the target table. When an alias is
provided, it completely hides the actual name of the table. For
example, given <code class="literal">MERGE INTO foo AS f</code>, the remainder of the
<code class="command">MERGE</code> statement must refer to this table as
<code class="literal">f</code> not <code class="literal">foo</code>.
</p></dd><dt><span class="term"><em class="replaceable"><code>source_table_name</code></em></span></dt><dd><p>
The name (optionally schema-qualified) of the source table, view, or
transition table. If <code class="literal">ONLY</code> is specified before the
table name, matching rows are included from the named table only. If
<code class="literal">ONLY</code> is not specified, matching rows are also included
from any tables inheriting from the named table. Optionally,
<code class="literal">*</code> can be specified after the table name to explicitly
indicate that descendant tables are included.
</p></dd><dt><span class="term"><em class="replaceable"><code>source_query</code></em></span></dt><dd><p>
A query (<code class="command">SELECT</code> statement or <code class="command">VALUES</code>
statement) that supplies the rows to be merged into the
target table.
Refer to the <a class="xref" href="sql-select.html" title="SELECT"><span class="refentrytitle">SELECT</span></a>
statement or <a class="xref" href="sql-values.html" title="VALUES"><span class="refentrytitle">VALUES</span></a>
statement for a description of the syntax.
</p></dd><dt><span class="term"><em class="replaceable"><code>source_alias</code></em></span></dt><dd><p>
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.
</p></dd><dt><span class="term"><em class="replaceable"><code>join_condition</code></em></span></dt><dd><p>
<em class="replaceable"><code>join_condition</code></em> is
an expression resulting in a value of type
<code class="type">boolean</code> (similar to a <code class="literal">WHERE</code>
clause) that specifies which rows in the
<em class="replaceable"><code>data_source</code></em>
match rows in the target table.
</p><div class="warning"><h3 class="title">Warning</h3><p>
Only columns from the target table
that attempt to match <em class="replaceable"><code>data_source</code></em>
rows should appear in <em class="replaceable"><code>join_condition</code></em>.
<em class="replaceable"><code>join_condition</code></em> subexpressions that
only reference the target table's
columns can affect which action is taken, often in surprising ways.
</p></div></dd><dt><span class="term"><em class="replaceable"><code>when_clause</code></em></span></dt><dd><p>
At least one <code class="literal">WHEN</code> clause is required.
</p><p>
If the <code class="literal">WHEN</code> clause specifies <code class="literal">WHEN MATCHED</code>
and the candidate change row matches a row in the
target table,
the <code class="literal">WHEN</code> clause is executed if the
<em class="replaceable"><code>condition</code></em> is
absent or it evaluates to <code class="literal">true</code>.
</p><p>
Conversely, if the <code class="literal">WHEN</code> clause specifies
<code class="literal">WHEN NOT MATCHED</code>
and the candidate change row does not match a row in the
target table,
the <code class="literal">WHEN</code> clause is executed if the
<em class="replaceable"><code>condition</code></em> is
absent or it evaluates to <code class="literal">true</code>.
</p></dd><dt><span class="term"><em class="replaceable"><code>condition</code></em></span></dt><dd><p>
An expression that returns a value of type <code class="type">boolean</code>.
If this expression for a <code class="literal">WHEN</code> clause
returns <code class="literal">true</code>, then the action for that clause
is executed for that row.
</p><p>
A condition on a <code class="literal">WHEN MATCHED</code> clause can refer to columns
in both the source and the target relations. A condition on a
<code class="literal">WHEN NOT MATCHED</code> 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.
</p></dd><dt><span class="term"><em class="replaceable"><code>merge_insert</code></em></span></dt><dd><p>
The specification of an <code class="literal">INSERT</code> 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.
</p><p>
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.
</p><p>
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.
</p><p>
Column names may not be specified more than once.
<code class="command">INSERT</code> actions cannot contain sub-selects.
</p><p>
Only one <code class="literal">VALUES</code> clause can be specified.
The <code class="literal">VALUES</code> clause can only refer to columns from
the source relation, since by definition there is no matching target row.
</p></dd><dt><span class="term"><em class="replaceable"><code>merge_update</code></em></span></dt><dd><p>
The specification of an <code class="literal">UPDATE</code> action that updates
the current row of the target table.
Column names may not be specified more than once.
</p><p>
Neither a table name nor a <code class="literal">WHERE</code> clause are allowed.
</p></dd><dt><span class="term"><em class="replaceable"><code>merge_delete</code></em></span></dt><dd><p>
Specifies a <code class="literal">DELETE</code> 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 <a class="xref" href="sql-delete.html" title="DELETE"><span class="refentrytitle">DELETE</span></a> command.
</p></dd><dt><span class="term"><em class="replaceable"><code>column_name</code></em></span></dt><dd><p>
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's name in the specification
of a target column.
</p></dd><dt><span class="term"><code class="literal">OVERRIDING SYSTEM VALUE</code></span></dt><dd><p>
Without this clause, it is an error to specify an explicit value
(other than <code class="literal">DEFAULT</code>) for an identity column defined
as <code class="literal">GENERATED ALWAYS</code>. This clause overrides that
restriction.
</p></dd><dt><span class="term"><code class="literal">OVERRIDING USER VALUE</code></span></dt><dd><p>
If this clause is specified, then any values supplied for identity
columns defined as <code class="literal">GENERATED BY DEFAULT</code> are ignored
and the default sequence-generated values are applied.
</p></dd><dt><span class="term"><code class="literal">DEFAULT VALUES</code></span></dt><dd><p>
All columns will be filled with their default values.
(An <code class="literal">OVERRIDING</code> clause is not permitted in this
form.)
</p></dd><dt><span class="term"><em class="replaceable"><code>expression</code></em></span></dt><dd><p>
An expression to assign to the column. If used in a
<code class="literal">WHEN MATCHED</code> clause, the expression can use values
from the original row in the target table, and values from the
<em class="replaceable"><code>data_source</code></em> row.
If used in a <code class="literal">WHEN NOT MATCHED</code> clause, the
expression can use values from the
<em class="replaceable"><code>data_source</code></em> row.
</p></dd><dt><span class="term"><code class="literal">DEFAULT</code></span></dt><dd><p>
Set the column to its default value (which will be <code class="literal">NULL</code>
if no specific default expression has been assigned to it).
</p></dd><dt><span class="term"><em class="replaceable"><code>sub-SELECT</code></em></span></dt><dd><p>
A <code class="literal">SELECT</code> 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 values from the original row in the target table,
and values from the <em class="replaceable"><code>data_source</code></em>
row.
</p></dd></dl></div></div><div class="refsect1" id="id-1.9.3.156.7"><h2>Outputs</h2><p>
On successful completion, a <code class="command">MERGE</code> command returns a command
tag of the form
</p><pre class="screen">
MERGE <em class="replaceable"><code>total_count</code></em>
</pre><p>
The <em class="replaceable"><code>total_count</code></em> is the total
number of rows changed (whether inserted, updated, or deleted).
If <em class="replaceable"><code>total_count</code></em> is 0, no rows
were changed in any way.
</p></div><div class="refsect1" id="id-1.9.3.156.8"><h2>Notes</h2><p>
The following steps take place during the execution of
<code class="command">MERGE</code>.
</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>
Perform any <code class="literal">BEFORE STATEMENT</code> triggers for all
actions specified, whether or not their <code class="literal">WHEN</code>
clauses match.
</p></li><li class="listitem"><p>
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,
</p><div class="orderedlist"><ol class="orderedlist" type="a"><li class="listitem"><p>
Evaluate whether each row is <code class="literal">MATCHED</code> or
<code class="literal">NOT MATCHED</code>.
</p></li><li class="listitem"><p>
Test each <code class="literal">WHEN</code> condition in the order
specified until one returns true.
</p></li><li class="listitem"><p>
When a condition returns true, perform the following actions:
</p><div class="orderedlist"><ol class="orderedlist" type="i"><li class="listitem"><p>
Perform any <code class="literal">BEFORE ROW</code> triggers that fire
for the action's event type.
</p></li><li class="listitem"><p>
Perform the specified action, invoking any check constraints on the
target table.
</p></li><li class="listitem"><p>
Perform any <code class="literal">AFTER ROW</code> triggers that fire for
the action's event type.
</p></li></ol></div></li></ol></div></li><li class="listitem"><p>
Perform any <code class="literal">AFTER STATEMENT</code> triggers for actions
specified, whether or not they actually occur. This is similar to the
behavior of an <code class="command">UPDATE</code> statement that modifies no rows.
</p></li></ol></div><p>
In summary, statement triggers for an event type (say,
<code class="command">INSERT</code>) will be fired whenever we
<span class="emphasis"><em>specify</em></span> an action of that kind.
In contrast, row-level triggers will fire only for the specific event type
being <span class="emphasis"><em>executed</em></span>.
So a <code class="command">MERGE</code> command might fire statement triggers for both
<code class="command">UPDATE</code> and <code class="command">INSERT</code>, even though only
<code class="command">UPDATE</code> row triggers were fired.
</p><p>
You should ensure that the join produces at most one candidate change row
for each target row. In other words, a target row shouldn't 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
<code class="command">MERGE</code>.
If the repeated action is an <code class="command">INSERT</code>, this will
cause a uniqueness violation, while a repeated <code class="command">UPDATE</code>
or <code class="command">DELETE</code> will cause a cardinality violation; the
latter behavior is required by the <acronym class="acronym">SQL</acronym> standard.
This differs from historical <span class="productname">PostgreSQL</span>
behavior of joins in <code class="command">UPDATE</code> and
<code class="command">DELETE</code> statements where second and subsequent
attempts to modify the same row are simply ignored.
</p><p>
If a <code class="literal">WHEN</code> clause omits an <code class="literal">AND</code>
sub-clause, it becomes the final reachable clause of that
kind (<code class="literal">MATCHED</code> or <code class="literal">NOT MATCHED</code>).
If a later <code class="literal">WHEN</code> 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.
</p><p>
The order in which rows are generated from the data source is
indeterminate by default.
A <em class="replaceable"><code>source_query</code></em> can be
used to specify a consistent ordering, if required, which might be
needed to avoid deadlocks between concurrent transactions.
</p><p>
There is no <code class="literal">RETURNING</code> clause with
<code class="command">MERGE</code>. Actions of <code class="command">INSERT</code>,
<code class="command">UPDATE</code> and <code class="command">DELETE</code> cannot contain
<code class="literal">RETURNING</code> or <code class="literal">WITH</code> clauses.
</p><p>
When <code class="command">MERGE</code> is run concurrently with other commands
that modify the target table, the usual transaction isolation rules
apply; see <a class="xref" href="transaction-iso.html" title="13.2. Transaction Isolation">Section 13.2</a> for an explanation
on the behavior at each isolation level.
You may also wish to consider using <code class="command">INSERT ... ON CONFLICT</code>
as an alternative statement which offers the ability to run an
<code class="command">UPDATE</code> if a concurrent <code class="command">INSERT</code>
occurs. There are a variety of differences and restrictions between
the two statement types and they are not interchangeable.
</p></div><div class="refsect1" id="id-1.9.3.156.9"><h2>Examples</h2><p>
Perform maintenance on <code class="literal">customer_accounts</code> based
upon new <code class="literal">recent_transactions</code>.
</p><pre class="programlisting">
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);
</pre><p>
</p><p>
Notice that this would be exactly equivalent to the following
statement because the <code class="literal">MATCHED</code> result does not change
during execution.
</p><pre class="programlisting">
MERGE INTO customer_account ca
USING (SELECT customer_id, transaction_value FROM recent_transactions) AS 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);
</pre><p>
</p><p>
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't allow entries that have zero stock.
</p><pre class="programlisting">
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;
</pre><p>
The <code class="literal">wine_stock_changes</code> table might be, for example, a
temporary table recently loaded into the database.
</p></div><div class="refsect1" id="id-1.9.3.156.10"><h2>Compatibility</h2><p>
This command conforms to the <acronym class="acronym">SQL</acronym> standard.
</p><p>
The <code class="literal">WITH</code> clause and <code class="literal">DO NOTHING</code>
action are extensions to the <acronym class="acronym">SQL</acronym> standard.
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