Add transform functions for various temporal typmod coercisions.

This enables ALTER TABLE to skip table and index rebuilds in some cases.

Noah Misch, with trivial changes by me.

src/backend/utils/adt/date.c

@@ -1210,6 +1210,17 @@ timetypmodout(PG_FUNCTION_ARGS)
 }
 
 
+/* time_transform()
+ * Flatten calls to time_scale() and timetz_scale() that solely represent
+ * increases in allowed precision.
+ */
+Datum
+time_transform(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_POINTER(TemporalTransform(MAX_TIME_PRECISION,
+										(Node *) PG_GETARG_POINTER(0)));
+}
+
 /* time_scale()
  * Adjust time type for specified scale factor.
  * Used by PostgreSQL type system to stuff columns.

src/backend/utils/adt/datetime.c

@@ -23,6 +23,8 @@
 #include "catalog/pg_type.h"
 #include "funcapi.h"
 #include "miscadmin.h"
+#include "nodes/nodeFuncs.h"
+#include "parser/parse_clause.h"
 #include "utils/builtins.h"
 #include "utils/date.h"
 #include "utils/datetime.h"
@@ -4141,6 +4143,39 @@ CheckDateTokenTables(void)
 	return ok;
 }
 
+/*
+ * Helper for temporal protransform functions.  Types time, timetz, timestamp
+ * and timestamptz each have a range of allowed precisions.  An unspecified
+ * precision is rigorously equivalent to the highest specifiable precision.
+ */
+Node *
+TemporalTransform(int32 max_precis, Node *node)
+{
+	FuncExpr   *expr = (FuncExpr *) node;
+	Node	   *typmod;
+	Node	   *ret = NULL;
+
+	if (!IsA(expr, FuncExpr))
+		return ret;
+
+	Assert(list_length(expr->args) == 2);
+	typmod = lsecond(expr->args);
+
+	if (IsA(typmod, Const))
+	{
+		Node	   *source = linitial(expr->args);
+		int32		old_precis = exprTypmod(source);
+		int32		new_precis = DatumGetInt32(((Const *) typmod)->constvalue);
+
+		if (new_precis == -1 ||
+			new_precis == max_precis ||
+			(old_precis != -1 && new_precis >= old_precis))
+			ret = relabel_to_typmod(source, new_precis);
+	}
+
+	return ret;
+}
+
 /*
  * This function gets called during timezone config file load or reload
  * to create the final array of timezone tokens.  The argument array

src/backend/utils/adt/timestamp.c

@@ -27,6 +27,8 @@
 #include "funcapi.h"
 #include "libpq/pqformat.h"
 #include "miscadmin.h"
+#include "nodes/nodeFuncs.h"
+#include "parser/parse_clause.h"
 #include "parser/scansup.h"
 #include "utils/array.h"
 #include "utils/builtins.h"
@@ -308,6 +310,21 @@ timestamptypmodout(PG_FUNCTION_ARGS)
 }
 
 
+/* timestamp_transform()
+ * Flatten calls to timestamp_scale() and timestamptz_scale() that solely
+ * represent increases in allowed precision.
+ */
+Datum
+timestamp_transform(PG_FUNCTION_ARGS)
+{
+	/*
+	 * timestamp_scale throws an error when the typmod is out of range, but we
+	 * can't get there from a cast: our typmodin will have caught it already.
+	 */
+	PG_RETURN_POINTER(TemporalTransform(MAX_TIMESTAMP_PRECISION,
+										(Node *) PG_GETARG_POINTER(0)));
+}
+
 /* timestamp_scale()
  * Adjust time type for specified scale factor.
  * Used by PostgreSQL type system to stuff columns.
@@ -745,6 +762,18 @@ interval_send(PG_FUNCTION_ARGS)
 	PG_RETURN_BYTEA_P(pq_endtypsend(&buf));
 }
 
+/*
+ * The interval typmod stores a "range" in its high 16 bits and a "precision"
+ * in its low 16 bits.  Both contribute to defining the resolution of the
+ * type.  Range addresses resolution granules larger than one second, and
+ * precision specifies resolution below one second.  This representation can
+ * express all SQL standard resolutions, but we implement them all in terms of
+ * truncating rightward from some position.  Range is a bitmap of permitted
+ * fields, but only the temporally-smallest such field is significant to our
+ * calculations.  Precision is a count of sub-second decimal places to retain.
+ * Setting all bits (INTERVAL_FULL_PRECISION) gives the same truncation
+ * semantics as choosing MAX_INTERVAL_PRECISION.
+ */
 Datum
 intervaltypmodin(PG_FUNCTION_ARGS)
 {
@@ -901,6 +930,63 @@ intervaltypmodout(PG_FUNCTION_ARGS)
 }
 
 
+/* interval_transform()
+ * Flatten superfluous calls to interval_scale().  The interval typmod is
+ * complex to permit accepting and regurgitating all SQL standard variations.
+ * For truncation purposes, it boils down to a single, simple granularity.
+ */
+Datum
+interval_transform(PG_FUNCTION_ARGS)
+{
+	FuncExpr   *expr = (FuncExpr *) PG_GETARG_POINTER(0);
+	Node	   *typmod;
+	Node	   *ret = NULL;
+
+	if (!IsA(expr, FuncExpr))
+		PG_RETURN_POINTER(ret);
+
+	Assert(list_length(expr->args) == 2);
+	typmod = lsecond(expr->args);
+
+	if (IsA(typmod, Const))
+	{
+		Node	   *source = linitial(expr->args);
+		int32		old_typmod = exprTypmod(source);
+		int32		new_typmod = DatumGetInt32(((Const *) typmod)->constvalue);
+		int			old_range;
+		int			old_precis;
+		int			new_range = INTERVAL_RANGE(new_typmod);
+		int			new_precis = INTERVAL_PRECISION(new_typmod);
+		int			new_range_fls;
+
+		if (old_typmod == -1)
+		{
+			old_range = INTERVAL_FULL_RANGE;
+			old_precis = INTERVAL_FULL_PRECISION;
+		}
+		else
+		{
+			old_range = INTERVAL_RANGE(old_typmod);
+			old_precis = INTERVAL_PRECISION(old_typmod);
+		}
+
+		/*
+		 * Temporally-smaller fields occupy higher positions in the range
+		 * bitmap.  Since only the temporally-smallest bit matters for length
+		 * coercion purposes, we compare the last-set bits in the ranges.
+		 */
+		new_range_fls = fls(new_range);
+		if (new_typmod == -1 ||
+			((new_range_fls >= SECOND ||
+			  new_range_fls >= fls(old_range)) &&
+			 (new_precis >= MAX_INTERVAL_PRECISION ||
+			  new_precis >= old_precis)))
+			ret = relabel_to_typmod(source, new_typmod);
+	}
+
+	PG_RETURN_POINTER(ret);
+}
+
 /* interval_scale()
  * Adjust interval type for specified fields.
  * Used by PostgreSQL type system to stuff columns.

src/include/catalog/catversion.h

@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201202072
+#define CATALOG_VERSION_NO	201202081
 
 #endif

src/include/catalog/pg_proc.h

@@ -1257,7 +1257,9 @@ DESCR("date difference preserving months and years");
 
 /* OIDS 1200 - 1299 */
 
-DATA(insert OID = 1200 (  interval			PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 1186 "1186 23" _null_ _null_ _null_ _null_ interval_scale _null_ _null_ _null_ ));
+DATA(insert OID = 3918 (  interval_transform PGNSP PGUID 12 1 0 0 0 f f f t f i 1 0 2281 "2281" _null_ _null_ _null_ _null_ interval_transform _null_ _null_ _null_ ));
+DESCR("transform an interval length coercion");
+DATA(insert OID = 1200 (  interval			PGNSP PGUID 12 1 0 0 3918 f f f t f i 2 0 1186 "1186 23" _null_ _null_ _null_ _null_ interval_scale _null_ _null_ _null_ ));
 DESCR("adjust interval precision");
 
 DATA(insert OID = 1215 (  obj_description	PGNSP PGUID 14 100 0 0 0 f f f t f s 2 0 25 "26 19" _null_ _null_ _null_ _null_ "select description from pg_catalog.pg_description where objoid = $1 and classoid = (select oid from pg_catalog.pg_class where relname = $2 and relnamespace = PGNSP) and objsubid = 0" _null_ _null_ _null_ ));
@@ -2732,7 +2734,9 @@ DATA(insert OID = 1953 (  byteane		   PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 16
 DATA(insert OID = 1954 (  byteacmp		   PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 23 "17 17" _null_ _null_ _null_ _null_ byteacmp _null_ _null_ _null_ ));
 DESCR("less-equal-greater");
 
-DATA(insert OID = 1961 (  timestamp		   PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 1114 "1114 23" _null_ _null_ _null_ _null_ timestamp_scale _null_ _null_ _null_ ));
+DATA(insert OID = 3917 (  timestamp_transform PGNSP PGUID 12 1 0 0 0 f f f t f i 1 0 2281 "2281" _null_ _null_ _null_ _null_ timestamp_transform _null_ _null_ _null_ ));
+DESCR("transform a timestamp length coercion");
+DATA(insert OID = 1961 (  timestamp		   PGNSP PGUID 12 1 0 0 3917 f f f t f i 2 0 1114 "1114 23" _null_ _null_ _null_ _null_ timestamp_scale _null_ _null_ _null_ ));
 DESCR("adjust timestamp precision");
 
 DATA(insert OID = 1965 (  oidlarger		   PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 26 "26 26" _null_ _null_ _null_ _null_ oidlarger _null_ _null_ _null_ ));
@@ -2740,11 +2744,13 @@ DESCR("larger of two");
 DATA(insert OID = 1966 (  oidsmaller	   PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 26 "26 26" _null_ _null_ _null_ _null_ oidsmaller _null_ _null_ _null_ ));
 DESCR("smaller of two");
 
-DATA(insert OID = 1967 (  timestamptz	   PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 1184 "1184 23" _null_ _null_ _null_ _null_ timestamptz_scale _null_ _null_ _null_ ));
+DATA(insert OID = 1967 (  timestamptz	   PGNSP PGUID 12 1 0 0 3917 f f f t f i 2 0 1184 "1184 23" _null_ _null_ _null_ _null_ timestamptz_scale _null_ _null_ _null_ ));
 DESCR("adjust timestamptz precision");
-DATA(insert OID = 1968 (  time			   PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 1083 "1083 23" _null_ _null_ _null_ _null_ time_scale _null_ _null_ _null_ ));
+DATA(insert OID = 3944 (  time_transform   PGNSP PGUID 12 1 0 0 0 f f f t f i 1 0 2281 "2281" _null_ _null_ _null_ _null_ time_transform _null_ _null_ _null_ ));
+DESCR("transform a time length coercion");
+DATA(insert OID = 1968 (  time			   PGNSP PGUID 12 1 0 0 3944 f f f t f i 2 0 1083 "1083 23" _null_ _null_ _null_ _null_ time_scale _null_ _null_ _null_ ));
 DESCR("adjust time precision");
-DATA(insert OID = 1969 (  timetz		   PGNSP PGUID 12 1 0 0 0 f f f t f i 2 0 1266 "1266 23" _null_ _null_ _null_ _null_ timetz_scale _null_ _null_ _null_ ));
+DATA(insert OID = 1969 (  timetz		   PGNSP PGUID 12 1 0 0 3944 f f f t f i 2 0 1266 "1266 23" _null_ _null_ _null_ _null_ timetz_scale _null_ _null_ _null_ ));
 DESCR("adjust time with time zone precision");
 
 DATA(insert OID = 2003 (  textanycat	   PGNSP PGUID 14 1 0 0 0 f f f t f v 2 0 25 "25 2776" _null_ _null_ _null_ _null_ "select $1 || $2::pg_catalog.text" _null_ _null_ _null_ ));

src/include/utils/date.h

@@ -154,6 +154,7 @@ extern Datum time_recv(PG_FUNCTION_ARGS);
 extern Datum time_send(PG_FUNCTION_ARGS);
 extern Datum timetypmodin(PG_FUNCTION_ARGS);
 extern Datum timetypmodout(PG_FUNCTION_ARGS);
+extern Datum time_transform(PG_FUNCTION_ARGS);
 extern Datum time_scale(PG_FUNCTION_ARGS);
 extern Datum time_eq(PG_FUNCTION_ARGS);
 extern Datum time_ne(PG_FUNCTION_ARGS);

src/include/utils/datetime.h

@@ -16,6 +16,7 @@
 #ifndef DATETIME_H
 #define DATETIME_H
 
+#include "nodes/nodes.h"
 #include "utils/timestamp.h"
 
 /* this struct is declared in utils/tzparser.h: */
@@ -298,6 +299,8 @@ extern int	DecodeUnits(int field, char *lowtoken, int *val);
 
 extern int	j2day(int jd);
 
+extern Node *TemporalTransform(int32 max_precis, Node *node);
+
 extern bool CheckDateTokenTables(void);
 
 extern void ConvertTimeZoneAbbrevs(TimeZoneAbbrevTable *tbl,

src/include/utils/timestamp.h

@@ -100,6 +100,7 @@ extern Datum timestamp_recv(PG_FUNCTION_ARGS);
 extern Datum timestamp_send(PG_FUNCTION_ARGS);
 extern Datum timestamptypmodin(PG_FUNCTION_ARGS);
 extern Datum timestamptypmodout(PG_FUNCTION_ARGS);
+extern Datum timestamp_transform(PG_FUNCTION_ARGS);
 extern Datum timestamp_scale(PG_FUNCTION_ARGS);
 extern Datum timestamp_eq(PG_FUNCTION_ARGS);
 extern Datum timestamp_ne(PG_FUNCTION_ARGS);
@@ -136,6 +137,7 @@ extern Datum interval_recv(PG_FUNCTION_ARGS);
 extern Datum interval_send(PG_FUNCTION_ARGS);
 extern Datum intervaltypmodin(PG_FUNCTION_ARGS);
 extern Datum intervaltypmodout(PG_FUNCTION_ARGS);
+extern Datum interval_transform(PG_FUNCTION_ARGS);
 extern Datum interval_scale(PG_FUNCTION_ARGS);
 extern Datum interval_eq(PG_FUNCTION_ARGS);
 extern Datum interval_ne(PG_FUNCTION_ARGS);