Adjust min/max values when changing sequence type

When changing the type of a sequence, adjust the min/max values of the
sequence if it looks like the previous values were the default values.
Previously, it would leave the old values in place, requiring manual
adjustments even in the usual/default cases.
Reviewed-by: Michael Paquier <michael.paquier@gmail.com>
Reviewed-by: Vitaly Burovoy <vitaly.burovoy@gmail.com>

doc/src/sgml/ref/alter_sequence.sgml

@@ -94,10 +94,15 @@ ALTER SEQUENCE [ IF EXISTS ] <replaceable class="parameter">name</replaceable> S
        </para>
 
        <para>
-        Note that changing the data type does not automatically change the
-        minimum and maximum values.  You can use the clauses <literal>NO
-        MINVALUE</literal> and <literal>NO MAXVALUE</literal> to adjust the
-        minimum and maximum values to the range of the new data type.
+        Changing the data type automatically changes the minimum and maximum
+        values of the sequence if and only if the previous minimum and maximum
+        values were the minimum or maximum value of the old data type (in
+        other words, if the sequence had been created using <literal>NO
+        MINVALUE</literal> or <literal>NO MAXVALUE</literal>, implicitly or
+        explicitly).  Otherwise, the minimum and maximum values are preserved,
+        unless new values are given as part of the same command.  If the
+        minimum and maximum values do not fit into the new data type, an error
+        will be generated.
        </para>
       </listitem>
      </varlistentry>

src/backend/commands/sequence.c

@@ -1232,6 +1232,8 @@ init_params(ParseState *pstate, List *options, bool isInit,
 	DefElem    *cache_value = NULL;
 	DefElem    *is_cycled = NULL;
 	ListCell   *option;
+	bool		reset_max_value = false;
+	bool		reset_min_value = false;
 
 	*owned_by = NIL;
 
@@ -1335,13 +1337,34 @@ init_params(ParseState *pstate, List *options, bool isInit,
 	/* AS type */
 	if (as_type != NULL)
 	{
-		seqform->seqtypid = typenameTypeId(pstate, defGetTypeName(as_type));
-		if (seqform->seqtypid != INT2OID &&
-			seqform->seqtypid != INT4OID &&
-			seqform->seqtypid != INT8OID)
+		Oid		newtypid = typenameTypeId(pstate, defGetTypeName(as_type));
+
+		if (newtypid != INT2OID &&
+			newtypid != INT4OID &&
+			newtypid != INT8OID)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 					 errmsg("sequence type must be smallint, integer, or bigint")));
+
+		if (!isInit)
+		{
+			/*
+			 * When changing type and the old sequence min/max values were the
+			 * min/max of the old type, adjust sequence min/max values to
+			 * min/max of new type.  (Otherwise, the user chose explicit
+			 * min/max values, which we'll leave alone.)
+			 */
+			if ((seqform->seqtypid == INT2OID && seqform->seqmax == PG_INT16_MAX) ||
+				(seqform->seqtypid == INT4OID && seqform->seqmax == PG_INT32_MAX) ||
+				(seqform->seqtypid == INT8OID && seqform->seqmax == PG_INT64_MAX))
+				reset_max_value = true;
+			if ((seqform->seqtypid == INT2OID && seqform->seqmin == PG_INT16_MIN) ||
+				(seqform->seqtypid == INT4OID && seqform->seqmin == PG_INT32_MIN) ||
+				(seqform->seqtypid == INT8OID && seqform->seqmin == PG_INT64_MIN))
+				reset_min_value = true;
+		}
+
+		seqform->seqtypid = newtypid;
 	}
 	else if (isInit)
 		seqform->seqtypid = INT8OID;
@@ -1375,9 +1398,9 @@ init_params(ParseState *pstate, List *options, bool isInit,
 		seqform->seqmax = defGetInt64(max_value);
 		seqdataform->log_cnt = 0;
 	}
-	else if (isInit || max_value != NULL)
+	else if (isInit || max_value != NULL || reset_max_value)
 	{
-		if (seqform->seqincrement > 0)
+		if (seqform->seqincrement > 0 || reset_max_value)
 		{
 			/* ascending seq */
 			if (seqform->seqtypid == INT2OID)
@@ -1412,11 +1435,9 @@ init_params(ParseState *pstate, List *options, bool isInit,
 		seqform->seqmin = defGetInt64(min_value);
 		seqdataform->log_cnt = 0;
 	}
-	else if (isInit || min_value != NULL)
+	else if (isInit || min_value != NULL || reset_min_value)
 	{
-		if (seqform->seqincrement > 0)
-			seqform->seqmin = 1; /* ascending seq */
-		else
+		if (seqform->seqincrement < 0 || reset_min_value)
 		{
 			/* descending seq */
 			if (seqform->seqtypid == INT2OID)
@@ -1426,6 +1447,8 @@ init_params(ParseState *pstate, List *options, bool isInit,
 			else
 				seqform->seqmin = PG_INT64_MIN;
 		}
+		else
+			seqform->seqmin = 1; /* ascending seq */
 		seqdataform->log_cnt = 0;
 	}
 

src/test/regress/sql/sequence.sql

@@ -23,15 +23,31 @@ DROP TABLE sequence_test_table;
 CREATE SEQUENCE sequence_test5 AS integer;
 CREATE SEQUENCE sequence_test6 AS smallint;
 CREATE SEQUENCE sequence_test7 AS bigint;
+CREATE SEQUENCE sequence_test8 AS integer MAXVALUE 100000;
+CREATE SEQUENCE sequence_test9 AS integer INCREMENT BY -1;
+CREATE SEQUENCE sequence_test10 AS integer MINVALUE -100000 START 1;
+CREATE SEQUENCE sequence_test11 AS smallint;
+CREATE SEQUENCE sequence_test12 AS smallint INCREMENT -1;
+CREATE SEQUENCE sequence_test13 AS smallint MINVALUE -32768;
+CREATE SEQUENCE sequence_test14 AS smallint MAXVALUE 32767 INCREMENT -1;
 CREATE SEQUENCE sequence_testx AS text;
 CREATE SEQUENCE sequence_testx AS nosuchtype;
 
-ALTER SEQUENCE sequence_test5 AS smallint;  -- fails
-ALTER SEQUENCE sequence_test5 AS smallint NO MINVALUE NO MAXVALUE;
-
 CREATE SEQUENCE sequence_testx AS smallint MAXVALUE 100000;
 CREATE SEQUENCE sequence_testx AS smallint MINVALUE -100000;
 
+ALTER SEQUENCE sequence_test5 AS smallint;  -- success, max will be adjusted
+ALTER SEQUENCE sequence_test8 AS smallint;  -- fail, max has to be adjusted
+ALTER SEQUENCE sequence_test8 AS smallint MAXVALUE 20000;  -- ok now
+ALTER SEQUENCE sequence_test9 AS smallint;  -- success, min will be adjusted
+ALTER SEQUENCE sequence_test10 AS smallint;  -- fail, min has to be adjusted
+ALTER SEQUENCE sequence_test10 AS smallint MINVALUE -20000;  -- ok now
+
+ALTER SEQUENCE sequence_test11 AS int;  -- max will be adjusted
+ALTER SEQUENCE sequence_test12 AS int;  -- min will be adjusted
+ALTER SEQUENCE sequence_test13 AS int;  -- min and max will be adjusted
+ALTER SEQUENCE sequence_test14 AS int;  -- min and max will be adjusted
+
 ---
 --- test creation of SERIAL column
 ---