*** a/src/backend/utils/adt/numeric.c
--- b/src/backend/utils/adt/numeric.c
***************
*** 712,717 **** numeric_send(PG_FUNCTION_ARGS)
--- 712,754 ----
  }
  
  
+ Datum
+ numeric_exemptor(PG_FUNCTION_ARGS)
+ {
+ 	int32		old_typmod = PG_GETARG_INT32(0);
+ 	int32		new_typmod = PG_GETARG_INT32(1);
+ 	int			old_scale;
+ 	int			new_scale;
+ 	int			old_precis;
+ 	int			new_precis;
+ 
+ 	/* Destination is unconstrained: never any work to do. */
+ 	if (new_typmod < VARHDRSZ)
+ 		PG_RETURN_INT32(COERCE_EXEMPT_NOCHANGE | COERCE_EXEMPT_NOERROR);
+ 
+ 	/*
+ 	 * Source is unconstrained, and destination is constrained.  A value like
+ 	 * 10^-1001 will always get truncated in this situation, so we can't help.
+ 	 */
+ 	if (old_typmod < VARHDRSZ)
+ 		PG_RETURN_INT32(0);
+ 
+ 	/* Each value stores its scale.  If the scale changes, we can't help. */
+ 	old_scale = (old_typmod - VARHDRSZ) & 0xffff;
+ 	new_scale = (new_typmod - VARHDRSZ) & 0xffff;
+ 	if (old_scale != new_scale)
+ 		PG_RETURN_INT32(0);
+ 
+ 	old_precis = (old_typmod - VARHDRSZ) >> 16 & 0xffff;
+ 	new_precis = (new_typmod - VARHDRSZ) >> 16 & 0xffff;
+ 	if (new_precis >= old_precis)
+ 		/* Precision increases with scale unchanged: never any work to do. */
+ 		PG_RETURN_INT32(COERCE_EXEMPT_NOCHANGE | COERCE_EXEMPT_NOERROR);
+ 
+ 	/* Precision falls with scale unchanged: might error, never changes data. */
+ 	PG_RETURN_INT32(COERCE_EXEMPT_NOCHANGE);
+ }
+ 
  /*
   * numeric() -
   *
*** a/src/include/catalog/catversion.h
--- b/src/include/catalog/catversion.h
***************
*** 53,58 ****
   */
  
  /*							yyyymmddN */
! #define CATALOG_VERSION_NO	201101103
  
  #endif
--- 53,58 ----
   */
  
  /*							yyyymmddN */
! #define CATALOG_VERSION_NO	201101104
  
  #endif
*** a/src/include/catalog/pg_cast.h
--- b/src/include/catalog/pg_cast.h
***************
*** 357,362 **** DATA(insert ( 1186 1186 1200 3543 i f ));
  DATA(insert ( 1266 1266 1969 3541 i f ));
  DATA(insert ( 1560 1560 1685 3817 i f ));
  DATA(insert ( 1562 1562 1687 3819 i f ));
! DATA(insert ( 1700 1700 1703 0 i f ));
  
  #endif   /* PG_CAST_H */
--- 357,362 ----
  DATA(insert ( 1266 1266 1969 3541 i f ));
  DATA(insert ( 1560 1560 1685 3817 i f ));
  DATA(insert ( 1562 1562 1687 3819 i f ));
! DATA(insert ( 1700 1700 1703 3818 i f ));
  
  #endif   /* PG_CAST_H */
*** a/src/include/catalog/pg_proc.h
--- b/src/include/catalog/pg_proc.h
***************
*** 2595,2600 **** DATA(insert OID = 2917 (  numerictypmodin		PGNSP PGUID 12 1 0 0 f f f t f i 1 0
--- 2595,2602 ----
  DESCR("I/O typmod");
  DATA(insert OID = 2918 (  numerictypmodout		PGNSP PGUID 12 1 0 0 f f f t f i 1 0 2275 "23" _null_ _null_ _null_ _null_	numerictypmodout _null_ _null_ _null_ ));
  DESCR("I/O typmod");
+ DATA(insert OID = 3818 (  numeric_exemptor  PGNSP PGUID 12 1 0 0 f f f t f i 3 0 23 "23 23 16" _null_ _null_ _null_ _null_ numeric_exemptor _null_ _null_ _null_ ));
+ DESCR("numeric cast exemptor");
  DATA(insert OID = 1703 ( numeric				PGNSP PGUID 12 1 0 0 f f f t f i 2 0 1700 "1700 23" _null_ _null_ _null_ _null_ numeric _null_ _null_ _null_ ));
  DESCR("adjust numeric to typmod precision/scale");
  DATA(insert OID = 1704 ( numeric_abs			PGNSP PGUID 12 1 0 0 f f f t f i 1 0 1700 "1700" _null_ _null_ _null_ _null_ numeric_abs _null_ _null_ _null_ ));
*** a/src/include/utils/builtins.h
--- b/src/include/utils/builtins.h
***************
*** 878,883 **** extern Datum numeric_recv(PG_FUNCTION_ARGS);
--- 878,884 ----
  extern Datum numeric_send(PG_FUNCTION_ARGS);
  extern Datum numerictypmodin(PG_FUNCTION_ARGS);
  extern Datum numerictypmodout(PG_FUNCTION_ARGS);
+ extern Datum numeric_exemptor(PG_FUNCTION_ARGS);
  extern Datum numeric (PG_FUNCTION_ARGS);
  extern Datum numeric_abs(PG_FUNCTION_ARGS);
  extern Datum numeric_uminus(PG_FUNCTION_ARGS);
*** a/src/test/regress/expected/alter_table.out
--- b/src/test/regress/expected/alter_table.out
***************
*** 1804,1845 **** DEBUG:  Rebuilding index "t_touchy_f_idx"
  DEBUG:  Rebuilding index "t_expr_idx"
  DEBUG:  Validating foreign key constraint "t_constraint3_fkey"
  ALTER TABLE t ALTER constraint3 TYPE numeric(7,2); -- verify; FK noop
! DEBUG:  Rewriting table "t"
! DEBUG:  Rebuilding index "t_constraint4_key"
! DEBUG:  Rebuilding index "t_integral_key"
! DEBUG:  Rebuilding index "t_rational_key"
! DEBUG:  Rebuilding index "t_daytimetz_key"
! DEBUG:  Rebuilding index "t_daytime_key"
! DEBUG:  Rebuilding index "t_stamptz_key"
! DEBUG:  Rebuilding index "t_stamp_key"
! DEBUG:  Rebuilding index "t_timegap_key"
! DEBUG:  Rebuilding index "t_bits_key"
! DEBUG:  Rebuilding index "t_network_key"
! DEBUG:  Rebuilding index "t_string_idx"
! DEBUG:  Rebuilding index "t_string_idx1"
! DEBUG:  Rebuilding index "t_strarr_idx"
! DEBUG:  Rebuilding index "t_square_idx"
! DEBUG:  Rebuilding index "t_touchy_f_idx"
! DEBUG:  Rebuilding index "t_expr_idx"
  DEBUG:  Validating foreign key constraint "t_constraint3_fkey"
  ALTER TABLE t ALTER constraint3 TYPE numeric(9,2); -- noop; FK noop
- DEBUG:  Rewriting table "t"
- DEBUG:  Rebuilding index "t_constraint4_key"
- DEBUG:  Rebuilding index "t_integral_key"
- DEBUG:  Rebuilding index "t_rational_key"
- DEBUG:  Rebuilding index "t_daytimetz_key"
- DEBUG:  Rebuilding index "t_daytime_key"
- DEBUG:  Rebuilding index "t_stamptz_key"
- DEBUG:  Rebuilding index "t_stamp_key"
- DEBUG:  Rebuilding index "t_timegap_key"
- DEBUG:  Rebuilding index "t_bits_key"
- DEBUG:  Rebuilding index "t_network_key"
- DEBUG:  Rebuilding index "t_string_idx"
- DEBUG:  Rebuilding index "t_string_idx1"
- DEBUG:  Rebuilding index "t_strarr_idx"
- DEBUG:  Rebuilding index "t_square_idx"
- DEBUG:  Rebuilding index "t_touchy_f_idx"
- DEBUG:  Rebuilding index "t_expr_idx"
  DEBUG:  Validating foreign key constraint "t_constraint3_fkey"
  -- Change a column with an incoming foreign key constraint.
  ALTER TABLE t ALTER constraint4 TYPE numeric(8,1); -- rewrite; FK error
--- 1804,1812 ----
  DEBUG:  Rebuilding index "t_expr_idx"
  DEBUG:  Validating foreign key constraint "t_constraint3_fkey"
  ALTER TABLE t ALTER constraint3 TYPE numeric(7,2); -- verify; FK noop
! DEBUG:  Verifying table "t"
  DEBUG:  Validating foreign key constraint "t_constraint3_fkey"
  ALTER TABLE t ALTER constraint3 TYPE numeric(9,2); -- noop; FK noop
  DEBUG:  Validating foreign key constraint "t_constraint3_fkey"
  -- Change a column with an incoming foreign key constraint.
  ALTER TABLE t ALTER constraint4 TYPE numeric(8,1); -- rewrite; FK error
***************
*** 1883,1923 **** DEBUG:  Rebuilding index "t_expr_idx"
  DEBUG:  Rebuilding index "t_constraint4_key"
  DEBUG:  Validating foreign key constraint "child_keycol_fkey"
  ALTER TABLE t ALTER constraint4 TYPE numeric(7,2); -- verify; FK noop
- DEBUG:  Rewriting table "t"
- DEBUG:  Rebuilding index "t_integral_key"
- DEBUG:  Rebuilding index "t_rational_key"
- DEBUG:  Rebuilding index "t_daytimetz_key"
- DEBUG:  Rebuilding index "t_daytime_key"
- DEBUG:  Rebuilding index "t_stamptz_key"
- DEBUG:  Rebuilding index "t_stamp_key"
- DEBUG:  Rebuilding index "t_timegap_key"
- DEBUG:  Rebuilding index "t_bits_key"
- DEBUG:  Rebuilding index "t_network_key"
- DEBUG:  Rebuilding index "t_string_idx"
- DEBUG:  Rebuilding index "t_string_idx1"
- DEBUG:  Rebuilding index "t_strarr_idx"
- DEBUG:  Rebuilding index "t_square_idx"
- DEBUG:  Rebuilding index "t_touchy_f_idx"
- DEBUG:  Rebuilding index "t_expr_idx"
  DEBUG:  Rebuilding index "t_constraint4_key"
  DEBUG:  Validating foreign key constraint "child_keycol_fkey"
  ALTER TABLE t ALTER constraint4 TYPE numeric(9,2); -- noop; FK noop
- DEBUG:  Rewriting table "t"
- DEBUG:  Rebuilding index "t_integral_key"
- DEBUG:  Rebuilding index "t_rational_key"
- DEBUG:  Rebuilding index "t_daytimetz_key"
- DEBUG:  Rebuilding index "t_daytime_key"
- DEBUG:  Rebuilding index "t_stamptz_key"
- DEBUG:  Rebuilding index "t_stamp_key"
- DEBUG:  Rebuilding index "t_timegap_key"
- DEBUG:  Rebuilding index "t_bits_key"
- DEBUG:  Rebuilding index "t_network_key"
- DEBUG:  Rebuilding index "t_string_idx"
- DEBUG:  Rebuilding index "t_string_idx1"
- DEBUG:  Rebuilding index "t_strarr_idx"
- DEBUG:  Rebuilding index "t_square_idx"
- DEBUG:  Rebuilding index "t_touchy_f_idx"
- DEBUG:  Rebuilding index "t_expr_idx"
  DEBUG:  Rebuilding index "t_constraint4_key"
  DEBUG:  Validating foreign key constraint "child_keycol_fkey"
  -- Type-specific tests.
--- 1850,1859 ----
  DEBUG:  Rebuilding index "t_constraint4_key"
  DEBUG:  Validating foreign key constraint "child_keycol_fkey"
  ALTER TABLE t ALTER constraint4 TYPE numeric(7,2); -- verify; FK noop
  DEBUG:  Rebuilding index "t_constraint4_key"
+ DEBUG:  Verifying table "t"
  DEBUG:  Validating foreign key constraint "child_keycol_fkey"
  ALTER TABLE t ALTER constraint4 TYPE numeric(9,2); -- noop; FK noop
  DEBUG:  Rebuilding index "t_constraint4_key"
  DEBUG:  Validating foreign key constraint "child_keycol_fkey"
  -- Type-specific tests.
***************
*** 2000,2040 **** DEBUG:  Rebuilding index "t_constraint4_key"
  DEBUG:  Rebuilding index "t_integral_key"
  DEBUG:  Rebuilding index "t_rational_key"
  ALTER TABLE t ALTER rational TYPE numeric(13,4);					-- noop
- DEBUG:  Rewriting table "t"
- DEBUG:  Rebuilding index "t_daytimetz_key"
- DEBUG:  Rebuilding index "t_daytime_key"
- DEBUG:  Rebuilding index "t_stamptz_key"
- DEBUG:  Rebuilding index "t_stamp_key"
- DEBUG:  Rebuilding index "t_timegap_key"
- DEBUG:  Rebuilding index "t_bits_key"
- DEBUG:  Rebuilding index "t_network_key"
- DEBUG:  Rebuilding index "t_string_idx"
- DEBUG:  Rebuilding index "t_string_idx1"
- DEBUG:  Rebuilding index "t_strarr_idx"
- DEBUG:  Rebuilding index "t_square_idx"
- DEBUG:  Rebuilding index "t_touchy_f_idx"
- DEBUG:  Rebuilding index "t_expr_idx"
- DEBUG:  Rebuilding index "t_constraint4_key"
- DEBUG:  Rebuilding index "t_integral_key"
  DEBUG:  Rebuilding index "t_rational_key"
  ALTER TABLE t ALTER rational TYPE numeric(11,4);					-- verify
- DEBUG:  Rewriting table "t"
- DEBUG:  Rebuilding index "t_daytimetz_key"
- DEBUG:  Rebuilding index "t_daytime_key"
- DEBUG:  Rebuilding index "t_stamptz_key"
- DEBUG:  Rebuilding index "t_stamp_key"
- DEBUG:  Rebuilding index "t_timegap_key"
- DEBUG:  Rebuilding index "t_bits_key"
- DEBUG:  Rebuilding index "t_network_key"
- DEBUG:  Rebuilding index "t_string_idx"
- DEBUG:  Rebuilding index "t_string_idx1"
- DEBUG:  Rebuilding index "t_strarr_idx"
- DEBUG:  Rebuilding index "t_square_idx"
- DEBUG:  Rebuilding index "t_touchy_f_idx"
- DEBUG:  Rebuilding index "t_expr_idx"
- DEBUG:  Rebuilding index "t_constraint4_key"
- DEBUG:  Rebuilding index "t_integral_key"
  DEBUG:  Rebuilding index "t_rational_key"
  ALTER TABLE t ALTER rational TYPE numeric;							-- noop
  DEBUG:  Rebuilding index "t_rational_key"
  ALTER TABLE t ALTER rational TYPE numeric(5,4);						-- verify-e
--- 1936,1945 ----
  DEBUG:  Rebuilding index "t_integral_key"
  DEBUG:  Rebuilding index "t_rational_key"
  ALTER TABLE t ALTER rational TYPE numeric(13,4);					-- noop
  DEBUG:  Rebuilding index "t_rational_key"
  ALTER TABLE t ALTER rational TYPE numeric(11,4);					-- verify
  DEBUG:  Rebuilding index "t_rational_key"
+ DEBUG:  Verifying table "t"
  ALTER TABLE t ALTER rational TYPE numeric;							-- noop
  DEBUG:  Rebuilding index "t_rational_key"
  ALTER TABLE t ALTER rational TYPE numeric(5,4);						-- verify-e