Implement remaining fields of information_schema.sequences view

Add new function pg_sequence_parameters that returns a sequence's start,
minimum, maximum, increment, and cycle values, and use that in the view.
(bug #5662; design suggestion by Tom Lane)

Also slightly adjust the view's column order and permissions after review of
SQL standard.

doc/src/sgml/information_schema.sgml

@@ -4139,31 +4139,42 @@ ORDER BY c.ordinal_position;
      </row>
 
      <row>
-      <entry><literal>maximum_value</literal></entry>
+      <entry><literal>start_value</literal></entry>
-      <entry><type>cardinal_number</type></entry>
+      <entry><type>character_data</type></entry>
-      <entry>Not yet implemented</entry>
+      <entry>The start value of the sequence</entry>
      </row>
 
      <row>
       <entry><literal>minimum_value</literal></entry>
-      <entry><type>cardinal_number</type></entry>
+      <entry><type>character_data</type></entry>
-      <entry>Not yet implemented</entry>
+      <entry>The minimum value of the sequence</entry>
+     </row>
+
+     <row>
+      <entry><literal>maximum_value</literal></entry>
+      <entry><type>character_data</type></entry>
+      <entry>The maximum value of the sequence</entry>
      </row>
 
      <row>
       <entry><literal>increment</literal></entry>
-      <entry><type>cardinal_number</type></entry>
+      <entry><type>character_data</type></entry>
-      <entry>Not yet implemented</entry>
+      <entry>The increment of the sequence</entry>
      </row>
 
      <row>
       <entry><literal>cycle_option</literal></entry>
       <entry><type>yes_or_no</type></entry>
-      <entry>Not yet implemented</entry>
+      <entry><literal>YES</literal> if the sequence cycles, else <literal>NO</literal></entry>
      </row>
     </tbody>
    </tgroup>
   </table>
+
+  <para>
+   Note that in accordance with the SQL standard, the start, minimum,
+   maximum, and increment values are returned as character strings.
+  </para>
  </sect1>
 
  <sect1 id="infoschema-sql-features">

src/backend/catalog/information_schema.sql

@@ -1430,16 +1430,18 @@ CREATE VIEW sequences AS
            CAST(64 AS cardinal_number) AS numeric_precision,
            CAST(2 AS cardinal_number) AS numeric_precision_radix,
            CAST(0 AS cardinal_number) AS numeric_scale,
-           CAST(null AS cardinal_number) AS maximum_value, -- FIXME
+           -- XXX: The following could be improved if we had LATERAL.
-           CAST(null AS cardinal_number) AS minimum_value, -- FIXME
+           CAST((pg_sequence_parameters(c.oid)).start_value AS character_data) AS start_value,
-           CAST(null AS cardinal_number) AS increment,     -- FIXME
+           CAST((pg_sequence_parameters(c.oid)).minimum_value AS character_data) AS minimum_value,
-           CAST(null AS yes_or_no) AS cycle_option    -- FIXME
+           CAST((pg_sequence_parameters(c.oid)).maximum_value AS character_data) AS maximum_value,
+           CAST((pg_sequence_parameters(c.oid)).increment AS character_data) AS increment,
+           CAST(CASE WHEN (pg_sequence_parameters(c.oid)).cycle_option THEN 'YES' ELSE 'NO' END AS yes_or_no) AS cycle_option
     FROM pg_namespace nc, pg_class c
     WHERE c.relnamespace = nc.oid
           AND c.relkind = 'S'
           AND (NOT pg_is_other_temp_schema(nc.oid))
           AND (pg_has_role(c.relowner, 'USAGE')
-               OR has_table_privilege(c.oid, 'SELECT, UPDATE') );
+               OR has_sequence_privilege(c.oid, 'SELECT, UPDATE, USAGE') );
 
 GRANT SELECT ON sequences TO PUBLIC;
 

src/backend/commands/sequence.c

@@ -24,6 +24,7 @@
 #include "commands/defrem.h"
 #include "commands/sequence.h"
 #include "commands/tablecmds.h"
+#include "funcapi.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "storage/bufmgr.h"
@@ -1420,6 +1421,56 @@ process_owned_by(Relation seqrel, List *owned_by)
 }
 
 
+/*
+ * Return sequence parameters, for use by information schema
+ */
+Datum
+pg_sequence_parameters(PG_FUNCTION_ARGS)
+{
+	Oid			relid = PG_GETARG_OID(0);
+	TupleDesc	tupdesc;
+	Datum		values[5];
+	bool		isnull[5];
+	SeqTable	elm;
+	Relation	seqrel;
+	Buffer		buf;
+	Form_pg_sequence seq;
+
+	/* open and AccessShareLock sequence */
+	init_sequence(relid, &elm, &seqrel);
+
+	if (pg_class_aclcheck(relid, GetUserId(), ACL_SELECT | ACL_UPDATE | ACL_USAGE) != ACLCHECK_OK)
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("permission denied for sequence %s",
+						RelationGetRelationName(seqrel))));
+
+	tupdesc = CreateTemplateTupleDesc(5, false);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "start_value", INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "minimum_value", INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "maximum_value", INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "increment", INT8OID, -1, 0);
+	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "cycle_option", BOOLOID, -1, 0);
+
+	BlessTupleDesc(tupdesc);
+
+	memset(isnull, 0, sizeof(isnull));
+
+	seq = read_info(elm, seqrel, &buf);
+
+	values[0] = Int64GetDatum(seq->start_value);
+	values[1] = Int64GetDatum(seq->min_value);
+	values[2] = Int64GetDatum(seq->max_value);
+	values[3] = Int64GetDatum(seq->increment_by);
+	values[4] = BoolGetDatum(seq->is_cycled);
+
+	UnlockReleaseBuffer(buf);
+	relation_close(seqrel, NoLock);
+
+	return HeapTupleGetDatum(heap_form_tuple(tupdesc, values, isnull));
+}
+
+
 void
 seq_redo(XLogRecPtr lsn, XLogRecord *record)
 {

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201101011
+#define CATALOG_VERSION_NO	201101021
 
 #endif

src/include/catalog/pg_proc.h

@@ -2120,6 +2120,8 @@ DATA(insert OID = 1576 (  setval			PGNSP PGUID 12 1 0 0 f f f t f v 2 0 20 "2205
 DESCR("set sequence value");
 DATA(insert OID = 1765 (  setval			PGNSP PGUID 12 1 0 0 f f f t f v 3 0 20 "2205 20 16" _null_ _null_ _null_ _null_ setval3_oid _null_ _null_ _null_ ));
 DESCR("set sequence value and iscalled status");
+DATA(insert OID = 3078 (  pg_sequence_parameters	PGNSP PGUID 12 1 0 0 f f f t f s 1 0 2249 "26" "{23,20,20,20,20,16}" "{i,o,o,o,o,o}" "{sequence_oid,start_value,minimum_value,maximum_value,increment,cycle_option}" _null_ pg_sequence_parameters _null_ _null_ _null_));
+DESCR("sequence parameters, for use by information schema");
 
 DATA(insert OID = 1579 (  varbit_in			PGNSP PGUID 12 1 0 0 f f f t f i 3 0 1562 "2275 26 23" _null_ _null_ _null_ _null_ varbit_in _null_ _null_ _null_ ));
 DESCR("I/O");

src/include/commands/sequence.h

@@ -69,6 +69,8 @@ extern Datum setval_oid(PG_FUNCTION_ARGS);
 extern Datum setval3_oid(PG_FUNCTION_ARGS);
 extern Datum lastval(PG_FUNCTION_ARGS);
 
+extern Datum pg_sequence_parameters(PG_FUNCTION_ARGS);
+
 extern void DefineSequence(CreateSeqStmt *stmt);
 extern void AlterSequence(AlterSeqStmt *stmt);
 extern void ResetSequence(Oid seq_relid);

src/test/regress/expected/sequence.out

@@ -220,6 +220,13 @@ SELECT nextval('sequence_test2');
        5
 (1 row)
 
+-- Information schema
+SELECT * FROM information_schema.sequences WHERE sequence_name IN ('sequence_test2');
+ sequence_catalog | sequence_schema | sequence_name  | data_type | numeric_precision | numeric_precision_radix | numeric_scale | start_value | minimum_value | maximum_value | increment | cycle_option 
+------------------+-----------------+----------------+-----------+-------------------+-------------------------+---------------+-------------+---------------+---------------+-----------+--------------
+ regression       | public          | sequence_test2 | bigint    |                64 |                       2 |             0 | 32          | 5             | 36            | 4         | YES
+(1 row)
+
 -- Test comments
 COMMENT ON SEQUENCE asdf IS 'won''t work';
 ERROR:  relation "asdf" does not exist

src/test/regress/sql/sequence.sql

@@ -85,6 +85,9 @@ SELECT nextval('sequence_test2');
 SELECT nextval('sequence_test2');
 SELECT nextval('sequence_test2');
 
+-- Information schema
+SELECT * FROM information_schema.sequences WHERE sequence_name IN ('sequence_test2');
+
 -- Test comments
 COMMENT ON SEQUENCE asdf IS 'won''t work';
 COMMENT ON SEQUENCE sequence_test2 IS 'will work';