diff options
Diffstat (limited to 'doc/src/sgml/arch-dev.sgml')
| -rw-r--r-- | doc/src/sgml/arch-dev.sgml | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/doc/src/sgml/arch-dev.sgml b/doc/src/sgml/arch-dev.sgml index 1315ce962df..8aeac029fcf 100644 --- a/doc/src/sgml/arch-dev.sgml +++ b/doc/src/sgml/arch-dev.sgml @@ -530,13 +530,15 @@ </para> <para> - The executor mechanism is used to evaluate all four basic SQL query + The executor mechanism is used to evaluate all five basic SQL query types: <command>SELECT</command>, <command>INSERT</command>, - <command>UPDATE</command>, and <command>DELETE</command>. + <command>UPDATE</command>, <command>DELETE</command>, and + <command>MERGE</command>. For <command>SELECT</command>, the top-level executor code only needs to send each row returned by the query plan tree off to the client. <command>INSERT ... SELECT</command>, - <command>UPDATE</command>, and <command>DELETE</command> + <command>UPDATE</command>, <command>DELETE</command>, and + <command>MERGE</command> are effectively <command>SELECT</command>s under a special top-level plan node called <literal>ModifyTable</literal>. </para> @@ -552,7 +554,13 @@ mark the old row deleted. For <command>DELETE</command>, the only column that is actually returned by the plan is the TID, and the <literal>ModifyTable</literal> node simply uses the TID to visit each - target row and mark it deleted. + target row and mark it deleted. For <command>MERGE</command>, the + planner joins the source and target relations, and includes all + column values required by any of the <literal>WHEN</literal> clauses, + plus the TID of the target row; this data is fed up to the + <literal>ModifyTable</literal> node, which uses the information to + work out which <literal>WHEN</literal> clause to execute, and then + inserts, updates or deletes the target row, as required. </para> <para> |