update

PostgreSQL/common.sql

@@ -1,5 +1,7 @@
--- search_path
+-- 修改用户的密码
-SHOW search_path;
+alter user postgres with password '123456';
+-- 查询所有用户
+select * from pg_catalog.pg_user;
 
 -- 查询表的 COLLATION VERSION
 SELECT
@@ -31,27 +33,5 @@ select r.ctid, r.* from study.r;
 -- "(0,3)",3,103
 
 -- 删除一条
-delete from study.r where id = 2;
+delete from study.r where id = 101;
--- 再重新查询，得到
+-- 得到
--- "(0,1)",1,101
--- "(0,3)",3,103
--- PostgreSQL 会保留空槽
-
--- 插入新数据
-insert into study.r values (104, 4);
--- 再重新查询，得到
--- "(0,1)",1,101
--- "(0,3)",3,103
--- "(0,4)",4,104
--- 可以看到使用了末尾的新槽位，而不是使用中间的新槽位
-
--- 执行清理
-vacuum full study.r;
--- 再次扫面，得到
--- "(0,1)",1,101
--- "(0,2)",3,103
--- "(0,3)",4,104
--- 看到空间已经回收
-
--- 查看数据类型
-select pg_typeof(EXTRACT(EPOCH FROM current_timestamp(0)))

PostgreSQL/function.sql

@@ -1,6 +0,0 @@
--- ROW 关键字生成一个元组
-SELECT ROW (1, 2, 3);
-
--- pg_column_size函数获取存储数据需要的字节数
-SELECT pg_column_size(ROW (1,2,3)); -- 36
-SELECT pg_column_size(ROW (1::int2, 2::int2, 3::int2)); -- 30

PostgreSQL/index.sql

@@ -1,2 +0,0 @@
--- 不阻塞的情况下创建索引
-create index concurrently idx_prism_timestamp on activities (timestamp);

PostgreSQL/time.sql

@@ -8,6 +8,3 @@ select msg_time at time zone 'Asia/Shanghai' from msg where id = 1;
 select msg_time at time zone 'UTC+8' from msg where id = 1;
 
 select to_timestamp(1761850339) AT TIME ZONE 'Asia/Shanghai';
-
--- 将当前时间转换为Unix时间戳
-select EXTRACT(EPOCH FROM current_timestamp(0)) - 60;

PostgreSQL/user.sql

@@ -1,4 +0,0 @@
--- 修改用户的密码
-alter user postgres with password '123456';
--- 查询所有用户
-select * from pg_catalog.pg_user;