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Revert MERGE patch

Browse Source 
This reverts commits d204ef6377,
83454e3c2b and a few more commits thereafter
(complete list at the end) related to MERGE feature.

While the feature was fully functional, with sufficient test coverage and
necessary documentation, it was felt that some parts of the executor and
parse-analyzer can use a different design and it wasn't possible to do that in
the available time. So it was decided to revert the patch for PG11 and retry
again in the future.

Thanks again to all reviewers and bug reporters.

List of commits reverted, in reverse chronological order:

 f1464c5380 Improve parse representation for MERGE
 ddb4158579 MERGE syntax diagram correction
 530e69e59b Allow cpluspluscheck to pass by renaming variable
 01b88b4df5 MERGE minor errata
 3af7b2b0d4 MERGE fix variable warning in non-assert builds
 a5d86181ec MERGE INSERT allows only one VALUES clause
 4b2d44031f MERGE post-commit review
 4923550c20 Tab completion for MERGE
 aa3faa3c7a WITH support in MERGE
 83454e3c2b New files for MERGE
 d204ef6377 MERGE SQL Command following SQL:2016

Author: Pavan Deolasee
Reviewed-by: Michael Paquier
This commit is contained in:
Simon Riggs
2018-04-12 11:22:56 +01:00
parent c9c875a28f
commit 08ea7a2291
100 changed files with 217 additions and 8629 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
doc/src/sgml/libpq.sgml
View File

@ -3917,11 +3917,9 @@ char *PQcmdTuples(PGresult *res);
<structname>PGresult</structname>. This function can only be used following
the execution of a <command>SELECT</command>, <command>CREATE TABLE AS</command>,
<command>INSERT</command>, <command>UPDATE</command>, <command>DELETE</command>,
<command>MERGE</command>, <command>MOVE</command>, <command>FETCH</command>,
or <command>COPY</command> statement, or an <command>EXECUTE</command> of a
prepared query that contains an <command>INSERT</command>,
<command>UPDATE</command>, <command>DELETE</command>
or <command>MERGE</command> statement.
<command>MOVE</command>, <command>FETCH</command>, or <command>COPY</command> statement,
or an <command>EXECUTE</command> of a prepared query that contains an
<command>INSERT</command>, <command>UPDATE</command>, or <command>DELETE</command> statement.
If the command that generated the <structname>PGresult</structname> was anything
else, <function>PQcmdTuples</function> returns an empty string. The caller
should not free the return value directly. It will be freed when

28
doc/src/sgml/mvcc.sgml
View File

@ -422,31 +422,6 @@ COMMIT;
<literal>11</literal>, which no longer matches the criteria.
</para>
<para>
The <command>MERGE</command> allows the user to specify various combinations
of <command>INSERT</command>, <command>UPDATE</command> or
<command>DELETE</command> subcommands. A <command>MERGE</command> command
with both <command>INSERT</command> and <command>UPDATE</command>
subcommands looks similar to <command>INSERT</command> with an
<literal>ON CONFLICT DO UPDATE</literal> clause but does not guarantee
that either <command>INSERT</command> and <command>UPDATE</command> will occur.
If MERGE attempts an UPDATE or DELETE and the row is concurrently updated
but the join condition still passes for the current target and the current
source tuple, then MERGE will behave the same as the UPDATE or DELETE commands
and perform its action on the latest version of the row, using standard
EvalPlanQual. MERGE actions can be conditional, so conditions must be
re-evaluated on the latest row, starting from the first action.
On the other hand, if the row is concurrently updated or deleted so that
the join condition fails, then MERGE will execute a NOT MATCHED action, if it
exists and the AND WHEN qual evaluates to true.
If MERGE attempts an INSERT and a unique index is present and a duplicate
row is concurrently inserted then a uniqueness violation is raised. MERGE
does not attempt to avoid the ERROR by attempting an UPDATE.
</para>
<para>
Because Read Committed mode starts each command with a new snapshot
that includes all transactions committed up to that instant,
@ -925,8 +900,7 @@ ERROR: could not serialize access due to read/write dependencies among transact
<para>
The commands <command>UPDATE</command>,
<command>DELETE</command>, <command>INSERT</command> and
<command>MERGE</command>
<command>DELETE</command>, and <command>INSERT</command>
acquire this lock mode on the target table (in addition to
<literal>ACCESS SHARE</literal> locks on any other referenced
tables). In general, this lock mode will be acquired by any

3
doc/src/sgml/plpgsql.sgml
View File

@ -1246,7 +1246,7 @@ EXECUTE format('SELECT count(*) FROM %I '
</programlisting>
Another restriction on parameter symbols is that they only work in
<command>SELECT</command>, <command>INSERT</command>, <command>UPDATE</command>, and
<command>DELETE</command> and <command>MERGE</command> commands. In other statement
<command>DELETE</command> commands. In other statement
types (generically called utility statements), you must insert
values textually even if they are just data values.
</para>
@ -1529,7 +1529,6 @@ GET DIAGNOSTICS integer_var = ROW_COUNT;
<listitem>
<para>
<command>UPDATE</command>, <command>INSERT</command>, and <command>DELETE</command>
and <command>MERGE</command>
statements set <literal>FOUND</literal> true if at least one
row is affected, false if no row is affected.
</para>

1
doc/src/sgml/ref/allfiles.sgml
View File

@ -159,7 +159,6 @@ Complete list of usable sgml source files in this directory.
<!ENTITY load SYSTEM "load.sgml">
<!ENTITY lock SYSTEM "lock.sgml">
<!ENTITY move SYSTEM "move.sgml">
<!ENTITY merge SYSTEM "merge.sgml">
<!ENTITY notify SYSTEM "notify.sgml">
<!ENTITY prepare SYSTEM "prepare.sgml">
<!ENTITY prepareTransaction SYSTEM "prepare_transaction.sgml">

7
doc/src/sgml/ref/create_policy.sgml
View File

@ -94,13 +94,6 @@ CREATE POLICY <replaceable class="parameter">name</replaceable> ON <replaceable
exist, a <quote>default deny</quote> policy is assumed, so that no rows will
be visible or updatable.
</para>
<para>
No separate policy exists for <command>MERGE</command>. Instead policies
defined for <literal>SELECT</literal>, <literal>INSERT</literal>,
<literal>UPDATE</literal> and <literal>DELETE</literal> are applied
while executing MERGE, depending on the actions that are activated.
</para>
</refsect1>
<refsect1>

11
doc/src/sgml/ref/insert.sgml
View File

@ -579,13 +579,6 @@ INSERT <replaceable>oid</replaceable> <replaceable class="parameter">count</repl
is a partition, an error will occur if one of the input rows violates
the partition constraint.
</para>
<para>
You may also wish to consider using <command>MERGE</command>, since that
allows mixed <command>INSERT</command>, <command>UPDATE</command> and
<command>DELETE</command> within a single statement.
See <xref linkend="sql-merge"/>.
</para>
</refsect1>
<refsect1>
@ -756,9 +749,7 @@ INSERT INTO distributors (did, dname) VALUES (10, 'Conrad International')
Also, the case in
which a column name list is omitted, but not all the columns are
filled from the <literal>VALUES</literal> clause or <replaceable>query</replaceable>,
is disallowed by the standard. If you prefer a more SQL Standard
conforming statement than <literal>ON CONFLICT</literal>, see
<xref linkend="sql-merge"/>.
is disallowed by the standard.
</para>
<para>

617
doc/src/sgml/ref/merge.sgml
View File

@ -1,617 +0,0 @@
<!--
doc/src/sgml/ref/merge.sgml
PostgreSQL documentation
-->
<refentry id="sql-merge">
<refmeta>
<refentrytitle>MERGE</refentrytitle>
<manvolnum>7</manvolnum>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>MERGE</refname>
<refpurpose>insert, update, or delete rows of a table based upon source data</refpurpose>
</refnamediv>
<refsynopsisdiv>
<synopsis>
[ WITH <replaceable class="parameter">with_query</replaceable> [, ...] ]
MERGE INTO <replaceable class="parameter">target_table_name</replaceable> [ [ AS ] <replaceable class="parameter">target_alias</replaceable> ]
USING <replaceable class="parameter">data_source</replaceable>
ON <replaceable class="parameter">join_condition</replaceable>
<replaceable class="parameter">when_clause</replaceable> [...]
where <replaceable class="parameter">data_source</replaceable> is
{ <replaceable class="parameter">source_table_name</replaceable> |
( source_query )
}
[ [ AS ] <replaceable class="parameter">source_alias</replaceable> ]
and <replaceable class="parameter">when_clause</replaceable> is
{ WHEN MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_update</replaceable> | <replaceable class="parameter">merge_delete</replaceable> } |
WHEN NOT MATCHED [ AND <replaceable class="parameter">condition</replaceable> ] THEN { <replaceable class="parameter">merge_insert</replaceable> | DO NOTHING }
}
and <replaceable class="parameter">merge_insert</replaceable> is
INSERT [( <replaceable class="parameter">column_name</replaceable> [, ...] )]
[ OVERRIDING { SYSTEM | USER } VALUE ]
{ VALUES ( { <replaceable class="parameter">expression</replaceable> | DEFAULT } [, ...] ) | DEFAULT VALUES }
and <replaceable class="parameter">merge_update</replaceable> is
UPDATE SET { <replaceable class="parameter">column_name</replaceable> = { <replaceable class="parameter">expression</replaceable> | DEFAULT } |
( <replaceable class="parameter">column_name</replaceable> [, ...] ) = ( { <replaceable class="parameter">expression</replaceable> | DEFAULT } [, ...] )
} [, ...]
and <replaceable class="parameter">merge_delete</replaceable> is
DELETE
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>MERGE</command> performs actions that modify rows in the
<replaceable class="parameter">target_table_name</replaceable>,
using the <replaceable class="parameter">data_source</replaceable>.
<command>MERGE</command> provides a single <acronym>SQL</acronym>
statement that can conditionally <command>INSERT</command>,
<command>UPDATE</command> or <command>DELETE</command> rows, a task
that would otherwise require multiple procedural language statements.
</para>
<para>
First, the <command>MERGE</command> command performs a join
from <replaceable class="parameter">data_source</replaceable> to
<replaceable class="parameter">target_table_name</replaceable>
producing zero or more candidate change rows. For each candidate change
row the status of <literal>MATCHED</literal> or <literal>NOT MATCHED</literal> is set
just once, after which <literal>WHEN</literal> clauses are evaluated
in the order specified. If one of them is activated, the specified
action occurs. No more than one <literal>WHEN</literal> clause can be
activated for any candidate change row.
</para>
<para>
<command>MERGE</command> actions have the same effect as
regular <command>UPDATE</command>, <command>INSERT</command>, or
<command>DELETE</command> commands of the same names. The syntax of
those commands is different, notably that there is no <literal>WHERE</literal>
clause and no tablename is specified. All actions refer to the
<replaceable class="parameter">target_table_name</replaceable>,
though modifications to other tables may be made using triggers.
</para>
<para>
When <literal>DO NOTHING</literal> action is specified, the source row is
skipped. Since actions are evaluated in the given order, <literal>DO
NOTHING</literal> can be handy to skip non-interesting source rows before
more fine-grained handling.
</para>
<para>
There is no MERGE privilege.
You must have the <literal>UPDATE</literal> privilege on the column(s)
of the <replaceable class="parameter">target_table_name</replaceable>
referred to in the <literal>SET</literal> clause
if you specify an update action, the <literal>INSERT</literal> privilege
on the <replaceable class="parameter">target_table_name</replaceable>
if you specify an insert action and/or the <literal>DELETE</literal>
privilege on the <replaceable class="parameter">target_table_name</replaceable>
if you specify a delete action on the
<replaceable class="parameter">target_table_name</replaceable>.
Privileges are tested once at statement start and are checked
whether or not particular <literal>WHEN</literal> clauses are activated
during the subsequent execution.
You will require the <literal>SELECT</literal> privilege on the
<replaceable class="parameter">data_source</replaceable> and any column(s)
of the <replaceable class="parameter">target_table_name</replaceable>
referred to in a <literal>condition</literal>.
</para>
<para>
MERGE is not supported if the <replaceable
class="parameter">target_table_name</replaceable> has
<literal>RULES</literal> defined on it.
See <xref linkend="rules"/> for more information about <literal>RULES</literal>.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="parameter">target_table_name</replaceable></term>
<listitem>
<para>
The name (optionally schema-qualified) of the target table to merge into.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">target_alias</replaceable></term>
<listitem>
<para>
A substitute name for the target table. When an alias is
provided, it completely hides the actual name of the table. For
example, given <literal>MERGE foo AS f</literal>, the remainder of the
<command>MERGE</command> statement must refer to this table as
<literal>f</literal> not <literal>foo</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">source_table_name</replaceable></term>
<listitem>
<para>
The name (optionally schema-qualified) of the source table, view or
transition table.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">source_query</replaceable></term>
<listitem>
<para>
A query (<command>SELECT</command> statement or <command>VALUES</command>
statement) that supplies the rows to be merged into the
<replaceable class="parameter">target_table_name</replaceable>.
Refer to the <xref linkend="sql-select"/>
statement or <xref linkend="sql-values"/>
statement for a description of the syntax.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">source_alias</replaceable></term>
<listitem>
<para>
A substitute name for the data source. When an alias is
provided, it completely hides whether table or query was specified.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">join_condition</replaceable></term>
<listitem>
<para>
<replaceable class="parameter">join_condition</replaceable> is
an expression resulting in a value of type
<type>boolean</type> (similar to a <literal>WHERE</literal>
clause) that specifies which rows in the
<replaceable class="parameter">data_source</replaceable>
match rows in the
<replaceable class="parameter">target_table_name</replaceable>.
</para>
<warning>
<para>
Only columns from <replaceable class="parameter">target_table_name</replaceable>
that attempt to match <replaceable class="parameter">data_source</replaceable>
rows should appear in <replaceable class="parameter">join_condition</replaceable>.
<replaceable class="parameter">join_condition</replaceable> subexpressions that
only reference <replaceable class="parameter">target_table_name</replaceable>
columns can only affect which action is taken, often in surprising ways.
</para>
</warning>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">when_clause</replaceable></term>
<listitem>
<para>
At least one <literal>WHEN</literal> clause is required.
</para>
<para>
If the <literal>WHEN</literal> clause specifies <literal>WHEN MATCHED</literal>
and the candidate change row matches a row in the
<replaceable class="parameter">target_table_name</replaceable>
the <literal>WHEN</literal> clause is activated if the
<replaceable class="parameter">condition</replaceable> is
absent or is present and evaluates to <literal>true</literal>.
If the <literal>WHEN</literal> clause specifies <literal>WHEN NOT MATCHED</literal>
and the candidate change row does not match a row in the
<replaceable class="parameter">target_table_name</replaceable>
the <literal>WHEN</literal> clause is activated if the
<replaceable class="parameter">condition</replaceable> is
absent or is present and evaluates to <literal>true</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">condition</replaceable></term>
<listitem>
<para>
An expression that returns a value of type <type>boolean</type>.
If this expression returns <literal>true</literal> then the <literal>WHEN</literal>
clause will be activated and the corresponding action will occur for
that row. The expression may not contain functions that possibly performs
writes to the database.
</para>
<para>
A condition on a <literal>WHEN MATCHED</literal> clause can refer to columns
in both the source and the target relation. A condition on a
<literal>WHEN NOT MATCHED</literal> 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.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">merge_insert</replaceable></term>
<listitem>
<para>
The specification of an <literal>INSERT</literal> 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.
</para>
<para>
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.
</para>
<para>
If the expression for any column is not of the correct data type,
automatic type conversion will be attempted.
</para>
<para>
If <replaceable class="parameter">target_table_name</replaceable>
is a partitioned table, each row is routed to the appropriate partition
and inserted into it.
If <replaceable class="parameter">target_table_name</replaceable>
is a partition, an error will occur if one of the input rows violates
the partition constraint.
</para>
<para>
Column names may not be specified more than once.
<command>INSERT</command> actions cannot contain sub-selects.
</para>
<para>
Only one <literal>VALUES</literal> clause can be specified.
The <literal>VALUES</literal> clause can only refer to columns from
the source relation, since by definition there is no matching target row.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">merge_update</replaceable></term>
<listitem>
<para>
The specification of an <literal>UPDATE</literal> action that updates
the current row of the <replaceable
class="parameter">target_table_name</replaceable>.
Column names may not be specified more than once.
</para>
<para>
Do not include the table name, as you would normally do with an
<xref linkend="sql-update"/> command.
For example, <literal>UPDATE tab SET col = 1</literal> is invalid. Also,
do not include a <literal>WHERE</literal> clause, since only the current
row can be updated. For example,
<literal>UPDATE SET col = 1 WHERE key = 57</literal> is invalid.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">merge_delete</replaceable></term>
<listitem>
<para>
Specifies a <literal>DELETE</literal> action that deletes the current row
of the <replaceable class="parameter">target_table_name</replaceable>.
Do not include the tablename or any other clauses, as you would normally
do with an <xref linkend="sql-delete"/> command.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">column_name</replaceable></term>
<listitem>
<para>
The name of a column in the <replaceable
class="parameter">target_table_name</replaceable>. 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.) When referencing a
column, do not include the table's name in the specification
of a target column.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>OVERRIDING SYSTEM VALUE</literal></term>
<listitem>
<para>
Without this clause, it is an error to specify an explicit value
(other than <literal>DEFAULT</literal>) for an identity column defined
as <literal>GENERATED ALWAYS</literal>. This clause overrides that
restriction.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>OVERRIDING USER VALUE</literal></term>
<listitem>
<para>
If this clause is specified, then any values supplied for identity
columns defined as <literal>GENERATED BY DEFAULT</literal> are ignored
and the default sequence-generated values are applied.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DEFAULT VALUES</literal></term>
<listitem>
<para>
All columns will be filled with their default values.
(An <literal>OVERRIDING</literal> clause is not permitted in this
form.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">expression</replaceable></term>
<listitem>
<para>
An expression to assign to the column. The expression can use the
old values of this and other columns in the table.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DEFAULT</literal></term>
<listitem>
<para>
Set the column to its default value (which will be NULL if no
specific default expression has been assigned to it).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="parameter">with_query</replaceable></term>
<listitem>
<para>
The <literal>WITH</literal> clause allows you to specify one or more
subqueries that can be referenced by name in the <command>MERGE</command>
query. See <xref linkend="queries-with"/> and <xref linkend="sql-select"/>
for details.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Outputs</title>
<para>
On successful completion, a <command>MERGE</command> command returns a command
tag of the form
<screen>
MERGE <replaceable class="parameter">total-count</replaceable>
</screen>
The <replaceable class="parameter">total-count</replaceable> is the total
number of rows changed (whether inserted, updated, or deleted).
If <replaceable class="parameter">total-count</replaceable> is 0, no rows
were changed in any way.
</para>
</refsect1>
<refsect1>
<title>Execution</title>
<para>
The following steps take place during the execution of
<command>MERGE</command>.
<orderedlist>
<listitem>
<para>
Perform any BEFORE STATEMENT triggers for all actions specified, whether or
not their <literal>WHEN</literal> clauses are activated during execution.
</para>
</listitem>
<listitem>
<para>
Perform a join from source to target table.
The resulting query will be optimized normally and will produce
a set of candidate change row. For each candidate change row
<orderedlist>
<listitem>
<para>
Evaluate whether each row is MATCHED or NOT MATCHED.
</para>
</listitem>
<listitem>
<para>
Test each WHEN condition in the order specified until one activates.
</para>
</listitem>
<listitem>
<para>
When activated, perform the following actions
<orderedlist>
<listitem>
<para>
Perform any BEFORE ROW triggers that fire for the action's event type.
</para>
</listitem>
<listitem>
<para>
Apply the action specified, invoking any check constraints on the
target table.
However, it will not invoke rules.
</para>
</listitem>
<listitem>
<para>
Perform any AFTER ROW triggers that fire for the action's event type.
</para>
</listitem>
</orderedlist>
</para>
</listitem>
</orderedlist>
</para>
</listitem>
<listitem>
<para>
Perform any AFTER STATEMENT triggers for actions specified, whether or
not they actually occur. This is similar to the behavior of an
<command>UPDATE</command> statement that modifies no rows.
</para>
</listitem>
</orderedlist>
In summary, statement triggers for an event type (say, INSERT) will
be fired whenever we <emphasis>specify</emphasis> an action of that kind. Row-level
triggers will fire only for the one event type <emphasis>activated</emphasis>.
So a <command>MERGE</command> might fire statement triggers for both
<command>UPDATE</command> and <command>INSERT</command>, even though only
<command>UPDATE</command> row triggers were fired.
</para>
<para>
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 will
cause an error. This can also occur if row triggers make changes to the
target table which are then subsequently modified by <command>MERGE</command>.
If the repeated action is an <command>INSERT</command> this will
cause a uniqueness violation while a repeated <command>UPDATE</command> or
<command>DELETE</command> will cause a cardinality violation; the latter behavior
is required by the <acronym>SQL</acronym> Standard. This differs from
historical <productname>PostgreSQL</productname> behavior of joins in
<command>UPDATE</command> and <command>DELETE</command> statements where second and
subsequent attempts to modify are simply ignored.
</para>
<para>
If a <literal>WHEN</literal> clause omits an <literal>AND</literal> clause it becomes
the final reachable clause of that kind (<literal>MATCHED</literal> or
<literal>NOT MATCHED</literal>). If a later <literal>WHEN</literal> clause of that kind
is specified it would be provably unreachable and an error is raised.
If a final reachable clause is omitted it is possible that no action
will be taken for a candidate change row.
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
The order in which rows are generated from the data source is indeterminate
by default. A <replaceable class="parameter">source_query</replaceable>
can be used to specify a consistent ordering, if required, which might be
needed to avoid deadlocks between concurrent transactions.
</para>
<para>
There is no <literal>RETURNING</literal> clause with <command>MERGE</command>.
Actions of <command>INSERT</command>, <command>UPDATE</command> and <command>DELETE</command>
cannot contain <literal>RETURNING</literal> or <literal>WITH</literal> clauses.
</para>
<tip>
<para>
You may also wish to consider using <command>INSERT ... ON CONFLICT</command> as an
alternative statement which offers the ability to run an <command>UPDATE</command>
if a concurrent <command>INSERT</command> occurs. There are a variety of
differences and restrictions between the two statement types and they are not
interchangeable.
</para>
</tip>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
Perform maintenance on CustomerAccounts based upon new Transactions.
<programlisting>
MERGE CustomerAccount CA
USING RecentTransactions T
ON T.CustomerId = CA.CustomerId
WHEN MATCHED THEN
UPDATE SET Balance = Balance + TransactionValue
WHEN NOT MATCHED THEN
INSERT (CustomerId, Balance)
VALUES (T.CustomerId, T.TransactionValue);
</programlisting>
notice that this would be exactly equivalent to the following
statement because the <literal>MATCHED</literal> result does not change
during execution
<programlisting>
MERGE CustomerAccount CA
USING (Select CustomerId, TransactionValue From RecentTransactions) AS T
ON CA.CustomerId = T.CustomerId
WHEN NOT MATCHED THEN
INSERT (CustomerId, Balance)
VALUES (T.CustomerId, T.TransactionValue)
WHEN MATCHED THEN
UPDATE SET Balance = Balance + TransactionValue;
</programlisting>
</para>
<para>
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.
<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;
</programlisting>
The wine_stock_changes table might be, for example, a temporary table
recently loaded into the database.
</para>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
This command conforms to the <acronym>SQL</acronym> standard.
</para>
<para>
The WITH clause and DO NOTHING action are extensions to the <acronym>SQL</acronym> standard.
</para>
</refsect1>
</refentry>

1
doc/src/sgml/reference.sgml
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@ -186,7 +186,6 @@
&listen;
&load;
&lock;
&merge;
&move;
&notify;
&prepare;

20
doc/src/sgml/trigger.sgml
View File

@ -182,26 +182,6 @@
will be fired.
</para>
<para>
No separate triggers are defined for <command>MERGE</command>. Instead,
statement-level or row-level <command>UPDATE</command>,
<command>DELETE</command> and <command>INSERT</command> triggers are fired
depending on what actions are specified in the <command>MERGE</command> query
and what actions are activated.
</para>
<para>
While running a <command>MERGE</command> command, statement-level
<literal>BEFORE</literal> and <literal>AFTER</literal> triggers are fired for
events specified in the actions of the <command>MERGE</command> command,
irrespective of whether the action is finally activated or not. This is same as
an <command>UPDATE</command> statement that updates no rows, yet
statement-level triggers are fired. The row-level triggers are fired only
when a row is actually updated, inserted or deleted. So it's perfectly legal
that while statement-level triggers are fired for certain type of action, no
row-level triggers are fired for the same kind of action.
</para>
<para>
Trigger functions invoked by per-statement triggers should always
return <symbol>NULL</symbol>. Trigger functions invoked by per-row