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达梦数据库查询模式名，表名，字段名查询所有的模式名SELECT DISTINCT object_name FROM ALL_OBJECTS WHERE OBJECT_TYPE = 'SCH'根据模式名查询表名SELECT table_name FROM dba_tables WHERE owner = '模式名'查询所有的模式名SELECT COLUMN_NAME FROM all_tab_columns WHERE onwer = '模式名' AND Table_Name = '表名'

sql 条件判断case when then '' else ''end消除重复distinctselect distinct username from user联合union 注意两个sql语句显示的类需要相同，如果查询数据相同会去除相同的只显示一条union all 解决上面的问题select username from user where id = 1unionselect username from user where id =