57 lines
1.4 KiB
SQL
57 lines
1.4 KiB
SQL
-- 修改用户的密码
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alter user postgres with password '123456';
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-- 查询所有用户
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select * from pg_catalog.pg_user;
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-- 查询表的 COLLATION VERSION
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SELECT
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datname,
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datcollversion,
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pg_collation_actual_version((SELECT oid FROM pg_collation WHERE collname = 'default')) as system_version
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FROM pg_database
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WHERE datname IN ('fortern', 'postgres', 'kt_shop')
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ORDER BY datname;
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-- 重建索引
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REINDEX DATABASE postgres;
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ALTER DATABASE postgres REFRESH COLLATION VERSION;
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REINDEX DATABASE fortern;
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ALTER DATABASE fortern REFRESH COLLATION VERSION;
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REINDEX DATABASE kt_shop;
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ALTER DATABASE kt_shop REFRESH COLLATION VERSION;
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-- 重置某表的某列的自增序列 [表名]_[列名]_seq
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ALTER SEQUENCE person_id_seq RESTART WITH 4284858;
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-- ctid 会返回一个元组，元组中第一个数字是 page number, 第二个是 slot number。
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select r.ctid, r.* from study.r;
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-- 得到
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-- "(0,1)",1,101
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-- "(0,2)",2,102
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-- "(0,3)",3,103
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-- 删除一条
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delete from study.r where id = 2;
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-- 再重新查询，得到
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-- "(0,1)",1,101
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-- "(0,3)",3,103
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-- PostgreSQL 会保留空槽
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-- 插入新数据
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insert into study.r values (104, 4);
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-- 再重新查询，得到
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-- "(0,1)",1,101
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-- "(0,3)",3,103
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-- "(0,4)",4,104
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-- 可以看到使用了末尾的新槽位，而不是使用中间的新槽位
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-- 执行清理
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vacuum full study.r;
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-- 再次扫面，得到
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-- "(0,1)",1,101
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-- "(0,2)",3,103
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-- "(0,3)",4,104
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-- 看到空间已经回收
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