ALL_TAB_COLS
ALL_TAB_COLS记录了用户所能访问的所有表字段相关的信息。
| 列名 | 类型 | 描述 |
| owner | name | 所有者 |
| table_name | information_schema.sql_identifier | 列所在的表或视图的名称 |
| column_name | information_schema.sql_identifier | 列名 |
| data_type | information_schema.character_data | 列的类型 |
| data_type_mod | text | 列的类型 |
| data_type_owner | name | |
| data_length | integer | 文本列的长度 |
| data_precision | information_schema.cardinal_number | 数字列的精度（位数） |
| data_scale | information_schema.cardinal_number | 数值列的比例 |
| nullable | information_schema.yes_or_no | 列是否可为空 |
| column_id | information_schema.cardinal_number | 表中列的相对位置 |
| default_length | text | |
| data_default | information_schema.character_data | 指定给列的默认值 |
| num_distinct | real | |
| low_value | text | |
| high_value | text | |
| density | double precision | |
| num_nulls | text | |
| num_buckets | text | |
| last_analyzed | text | |
| sample_size | text | |
| character_set_name | text | |
| char_col_decl_length | information_schema.cardinal_number | |
| global_stats | text | |
| user_stats | text | |
| avg_col_len | integer | |
| char_length | information_schema.cardinal_number | |
| char_used | text | |
| v80_fmt_image | text | |
| data_upgraded | text | |
| hidden_column | text | |
| virtual_column | text | |
| segment_column_id | text | |
| internal_column_id | information_schema.cardinal_number | |
| histogram | text | |
| qualified_col_name | information_schema.sql_identifier |
