ST_SetBandNoDataValue — 设置表示无数据的给定波段的值。如果没有指定波段，则假定为波段 1。要将波段标记为没有 nodata 值，请将 nodata 值 = NULL。
raster ST_SetBandNoDataValue(raster rast, double precision nodatavalue);
raster ST_SetBandNoDataValue(raster rast, integer band, double precision nodatavalue, boolean forcechecking=false);
-- change just first band no data value
UPDATE dummy_rast
SET rast = ST_SetBandNoDataValue(rast,1, 254)
WHERE rid = 2;
-- change no data band value of bands 1,2,3
UPDATE dummy_rast
SET rast =
ST_SetBandNoDataValue(
ST_SetBandNoDataValue(
ST_SetBandNoDataValue(
rast,1, 254)
,2,99),
3,108)
WHERE rid = 2;
-- wipe out the nodata value this will ensure all pixels are considered for all processing functions
UPDATE dummy_rast
SET rast = ST_SetBandNoDataValue(rast,1, NULL)
WHERE rid = 2;