sql脚本函数编写postgresql数据库实现解析

CREATE SEQUENCE global_id_sequence;CREATE OR REPLACE FUNCTION seq_id(OUT result bigint) AS $$DECLARE  our_epoch bigint := 1314220021721;  seq_id bigint;  now_millis bigint;  -- the id of this DB shard, must be set for each  -- schema shard you have - you could pass this as a parameter too  shard_id int := 1;BEGIN  SELECT nextval('global_id_sequence') % 1024 INTO seq_id;  SELECT FLOOR(EXTRACT(EPOCH FROM clock_timestamp()) * 1000) INTO now_millis;  result := (now_millis - our_epoch) << 23;  result := result | (shard_id << 10);  result := result | (seq_id);END;$$ LANGUAGE PLPGSQL;<!--alter function seq_id(out bigint) owner to postgres;-->

do language plpgsql$$beginupdate grade set grade = 90 where sno = '20161003';end$$