diff --git a/Doc/ OpenGauss常用命令.txt b/Doc/ OpenGauss常用命令.txt
index 325a1d2..3bc418d 100644
--- a/Doc/ OpenGauss常用命令.txt	
+++ b/Doc/ OpenGauss常用命令.txt	
@@ -30,4 +30,54 @@ WHERE
 	AND A.attrelid = C.oid
 
 # 需要注意修改一下
-mysql:ifnull <--> pgsql:coalesce
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+mysql:ifnull <--> pgsql:coalesce
+
+#************************************************************************************************************************************
+# 查看有哪些序列
+select * from pg_class where relkind='S';
+
+# 创建一个序列
+create sequence seq_t_base_student
+increment  by 1         --步长
+minvalue 1              --最小值
+maxvalue 999999999      --最大值
+start 1                 --起始值
+cache 1                 --每次生成几个值
+cycle;                  --到达最大值或最小值循环(不加默认不循环)
+
+
+# 查看当前序列的值
+select * from seq_t_base_student;
+
+# 删除序列
+drop sequence seq_t_base_student;
+
+# 使用序列
+DROP TABLE IF EXISTS "public"."t_base_student";
+CREATE TABLE "public"."t_base_student" (
+  "student_id" int4 NOT NULL DEFAULT nextval('seq_t_base_student'::regclass),
+  "student_name" varchar(255) COLLATE "pg_catalog"."default"
+);
+
+-- ----------------------------
+-- Records of t_base_student
+-- ----------------------------
+INSERT INTO "public"."t_base_student" VALUES (1, '张三');
+INSERT INTO "public"."t_base_student" VALUES (2, '李四');
+
+-- ----------------------------
+-- Primary Key structure for table t_base_student
+-- ----------------------------
+ALTER TABLE "public"."t_base_student" ADD CONSTRAINT "t_base_student_pkey" PRIMARY KEY ("student_id");
+
+
+
+# 查询孤儿序列（没有字段绑定的，也没有被使用，在系统中占用资源，如果序列被绑定到一个serial类型的字段，删除该表时，序列会被自动删除，如果时int类型，则不会被删除，所以在大型数据库系统中应注意过多孤儿序列的产生）
+SELECT ns.nspname AS schema_name, seq.relname AS seq_name
+FROM pg_class AS seq
+JOIN pg_namespace ns ON (seq.relnamespace=ns.oid)
+WHERE seq.relkind = 'S'
+  AND NOT EXISTS (SELECT * FROM pg_depend WHERE objid=seq.oid AND deptype='a')
+ORDER BY seq.relname;
+
+结论：PG中一旦使用了序列，就不能手动向这个字段写入数值，否则序列不变化，会导致主键重复！
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