[HACKERS] CREATE FOREIGN TABLE ( ... LIKE ... )

[David Fetter]

Folks,

Please find attached a patch implementing and documenting, to some
extent, $subject.  I did this in aid of being able to import SQL
standard catalogs and other entities where a known example could
provide a template for a foreign table.

Should there be errhint()s, too?  Should we pile up all such errors
and mention them at the end rather than simply bailing on the first
one?

TBD: regression tests.

Cheers,
David.
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diff --git a/doc/src/sgml/ref/create_foreign_table.sgml 
b/doc/src/sgml/ref/create_foreign_table.sgml
index 1ef4b5e..4a8e265 100644
--- a/doc/src/sgml/ref/create_foreign_table.sgml
+++ b/doc/src/sgml/ref/create_foreign_table.sgml
@@ -20,6 +20,7 @@
 <synopsis>
 CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable 
class="PARAMETER">table_name</replaceable> ( [
     <replaceable class="PARAMETER">column_name</replaceable> <replaceable 
class="PARAMETER">data_type</replaceable> [ OPTIONS ( <replaceable 
class="PARAMETER">option</replaceable> '<replaceable 
class="PARAMETER">value</replaceable>' [, ... ] ) ] [ COLLATE 
<replaceable>collation</replaceable> ] [ <replaceable 
class="PARAMETER">column_constraint</replaceable> [ ... ] ]
+    | LIKE <replaceable>source_table</replaceable> [ 
<replaceable>like_option</replaceable> ... ] }
     [, ... ]
 ] )
   SERVER <replaceable class="parameter">server_name</replaceable>
@@ -114,6 +115,15 @@ CREATE FOREIGN TABLE [ IF NOT EXISTS ] <replaceable 
class="PARAMETER">table_name
    </varlistentry>
 
    <varlistentry>
+    <term><literal>LIKE 
<replaceable>source_table</replaceable></literal></term>
+    <listitem>
+     <para>
+      The <literal>LIKE</literal> clause specifies a table from which
+      the new foreign table automatically copies all column names and their 
data types.
+     </para>
+   </varlistentry>
+
+   <varlistentry>
     <term><literal>NOT NULL</></term>
     <listitem>
      <para>
diff --git a/src/backend/parser/parse_utilcmd.c 
b/src/backend/parser/parse_utilcmd.c
index 19d19e5f..152fa01 100644
--- a/src/backend/parser/parse_utilcmd.c
+++ b/src/backend/parser/parse_utilcmd.c
@@ -649,7 +649,7 @@ transformTableConstraint(CreateStmtContext *cxt, Constraint 
*constraint)
 /*
  * transformTableLikeClause
  *
- * Change the LIKE <srctable> portion of a CREATE TABLE statement into
+ * Change the LIKE <srctable> portion of a CREATE [FOREIGN] TABLE statement 
into
  * column definitions which recreate the user defined column portions of
  * <srctable>.
  */
@@ -669,10 +669,12 @@ transformTableLikeClause(CreateStmtContext *cxt, 
TableLikeClause *table_like_cla
                                                                          
table_like_clause->relation->location);
 
        /* we could support LIKE in many cases, but worry about it another day 
*/
+       /* Let's see whether just dropping this enables LIKE :)
        if (cxt->isforeign)
                ereport(ERROR,
                                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                                 errmsg("LIKE is not supported for creating 
foreign tables")));
+        */
 
        relation = relation_openrv(table_like_clause->relation, 
AccessShareLock);
 
@@ -689,6 +691,25 @@ transformTableLikeClause(CreateStmtContext *cxt, 
TableLikeClause *table_like_cla
        cancel_parser_errposition_callback(&pcbstate);
 
        /*
+        * For foreign tables, disallow some options.
+        */
+       if (cxt->isforeign)
+       {
+               if (table_like_clause->options & CREATE_TABLE_LIKE_CONSTRAINTS)
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                                        errmsg("ERROR: foreign tables do not 
support LIKE INCLUDING CONSTRAINTS")));
+               else if (table_like_clause->options & CREATE_TABLE_LIKE_INDEXES)
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                                        errmsg("ERROR: foreign tables do not 
support LIKE INCLUDING INDEXES")));
+               else if (table_like_clause->options & CREATE_TABLE_LIKE_STORAGE)
+                       ereport(ERROR,
+                                       (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                                        errmsg("ERROR: foreign tables do not 
support LIKE INCLUDING STORAGE")));
+       }
+
+       /*
         * Check for privileges
         */
        if (relation->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)

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