July 2023
Intermediate to advanced
278 pages
5h 40m
Chinese
Content preview from Trino 权威指南：原书第2版
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136
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第
8
章
可以更改现有
schema
的名称：
ALTER SCHEMA name RENAME TO new_name
还支持删除一个
schema
：
DROP SCHEMA [ IF EXISTS ] schema_name
当你不想让语句在
schema
不存在时报错，可以指定
IF EXISTS
。在成功删除
schema
之
前，你需要删除
schema
中所有的表。有些数据库系统支持
CASCADE
关键字，表示
DROP
语句将
schema
中所有的对象都删除，但是
Trino
现阶段并不支持该关键字。
8.5 information schema
information schema
是
SQL
标准的一部分。在
Trino
中，每一个
catalog
都有自己的
information_schema
，其中包含关于
schema
、列、表、视图等对象的元数据。
SHOW
TABLES
、
SHOW SCHEMA
等命令都是从
information schema
中获取信息的。
information schema
对于第三方商业智能软件来说必不可少。很多
BI
软件都会通过查询
它来获取
catalog
中对象的信息，以便知道有哪些对象存在。
在每个连接器中，
information schema
都有
9
个视图。某些连接器可能不支持一些功能，
比如
roles
，这时候查询对应的
information_schema
会报不支持错误：
SHOW TABLES IN system.information_schema;
Table
-------------------------------- ...
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