对指定用户的select权限和create权限如何修改？

无法直接修改，可以先revoke在重新grant,具体语法如下：
回收权限：
REVOKE [ GRANT OPTION FOR ]
{ { SELECT | INSERT | UPDATE | DELETE | TRUNCATE | REFERENCES | ALTER | DROP | COMMENT | INDEX | VACUUM }[, ...]
| ALL [ PRIVILEGES ] }
ON { [ TABLE ] table_name [, ...]
| ALL TABLES IN SCHEMA schema_name [, ...] }
FROM { [ GROUP ] role_name | PUBLIC } [, ...]
[ CASCADE | RESTRICT ];
授权语法：
GRANT { { SELECT | INSERT | UPDATE | DELETE | TRUNCATE | REFERENCES | ALTER | DROP | COMMENT | INDEX | VACUUM } [, ...]
| ALL [ PRIVILEGES ] }
ON { [ TABLE ] table_name [, ...]
| ALL TABLES IN SCHEMA schema_name [, ...] }
TO { [ GROUP ] role_name | PUBLIC } [, ...]
[ WITH GRANT OPTION ];
具体根据实际回收或赋予权限

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