=> SHOW rds.extensions;

rds.extensions                                                                                                                                 
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 btree_gin,btree_gist,chkpass,citext,cube,dblink,dict_int,dict_xsyn,earthdistance,fuzzystrmatch,hstore,intagg,intarray,isn,ltree,pgcrypto,pgrowlocks,pg_trgm,plperl,plpgsql,pltcl,postgis,postgis_tiger_geocoder,postgis_topology,sslinfo,tablefunc,tsearch2,unaccent,uuid-ossp
(1 row)

你可以看到,uuid-ossp扩展名确实存在.但是,当我调用uuid_v4生成函数时,它会失败：

CREATE TABLE my_table (
    id uuid DEFAULT uuid_generate_v4() NOT NULL,name character varying(32) NOT NULL,);

这是怎么回事？