postgres序列（serial）和类型：https://www.cnblogs.com/alianbog/p/5654604.html
序列：https://www.cnblogs.com/mchina/archive/2013/04/10/3012493.html
serial序列其实就是当不给此字段赋值的时候，自动获取下一个值（唯一），可以当作自增主键
create table tbl_serial(a serial,b varchar(2));
DROP SEQUENCE if EXISTS "public"."quake_data_id_seq"; CREATE SEQUENCE "public"."quake_data_id_seq" INCREMENT 1 MINVALUE 1 MAXVALUE 9223372036854775807 START 1 CACHE 1; DROP TABLE if EXISTS "public"."quake_data"; CREATE TABLE "public"."quake_data" ( "id" int4 NOT NULL DEFAULT nextval(‘quake_data_id_seq‘::regclass), "quake_id" int4 DEFAULT 0, "channel_id" varchar(40) COLLATE "pg_catalog"."default" DEFAULT NULL, "gauge_data" float8 DEFAULT NULL, "guage_time" timestamp(6) DEFAULT NULL, CONSTRAINT "1" PRIMARY KEY ("id") ) ; ALTER TABLE "public"."quake_data" OWNER TO "username"; COMMENT ON COLUMN "public"."quake_data"."quake_id" IS ‘事件id‘; COMMENT ON COLUMN "public"."quake_data"."channel_id" IS ‘点号‘; COMMENT ON COLUMN "public"."quake_data"."gauge_data" IS ‘测量值‘; COMMENT ON COLUMN "public"."quake_data"."guage_time" IS ‘测量时间‘;
创建序列示例：
CREATE SEQUENCE "public"."quake_data_id_seq" INCREMENT 1 MINVALUE 1 MAXVALUE 9223372036854775807 START 1 CACHE 1;
修改字段默认值：
ALTER TABLE "public"."ttt" ALTER COLUMN "id" TYPE int4 USING "quake_id"::int4; ALTER TABLE "public"."ttt" ALTER COLUMN "id" SET DEFAULT nextval(‘ttt_id_seq‘::regclass);
PS： 具体alter命令可以取官方网站查询：https://www.postgresql.org/docs/9.1/sql-altertable.html
还有一个方便的方法：使用navticat修改一个字段（属性，添加字段，删除字段等等都可以），然后点击SQL预览，就可以看到对应的sql命令了
比如下面图片演示，更改guage_time字段不能为空
然后点击SQL预览， 显示sql语句：
ALTER TABLE "public"."ttt" ALTER COLUMN "guage_time" SET NOT NULL;
原文：https://www.cnblogs.com/zhzhlong/p/11460327.html