lob字段压缩

空间节约的程度依赖于LOB段数据的存储类型。

| 表  |  情况 |  备注 |
| :------------ | :------------ | :------------ |
| jhmr_file_content  | 无法压缩  |   |
| jhmr_file_content_log  | 无法压缩  |   |
| jhmr_file_content_CDA  | 压缩6倍  |   |
| jhmr_file_content_HTM  | 压缩2倍  |   |
| jhmr_file_content_text  | 压缩1/4倍  |   ||

```sql
SELECT (A.BYTES / 1024 / 1024) AS SIZE_MB,
         A.owner,
         case
           when A.segment_type = 'LOBSEGMENT' then
            (SELECT B.TABLE_NAME || '【' || B.COLUMN_NAME||'】'
               FROM DBA_LOBS B
              WHERE A.owner = B.OWNER
                AND A.segment_name = B.SEGMENT_NAME)
           else
            A.segment_name
         end as segment_name，
         a.segment_type
    FROM DBA_SEGMENTS A
   WHERE A.owner IN ('JHEMR', 'JHFILE','JHCDR','JHLCP','JHNIS','JHCDAS')
   ORDER BY BYTES DESC;
```

```sql
   select t.COMPRESSION,t.COMPRESS_FOR,t.* from user_tables t where t.TABLE_NAME like '%SPP%';
```

```sql
ALTER TABLE SPP_COM COMPRESS FOR OLTP
   create table SPP_COM
(
  id      VARCHAR2(50),
  content BLOB
)
tablespace TSP_JHEMR;

create table SPP_NOT_COM
(
  id      VARCHAR2(50),
  content BLOB
)
tablespace TSP_JHEMR;
ALTER TABLE SPP_COM MODIFY LOB(CONTENT) (COMPRESS HIGH);
select * From dba_lobs t where t.OWNER='JHEMR' and t.TABLE_NAME like '%SPP%';
select * From dba_lobs t where t.OWNER='JHEMR' and t.TABLE_NAME like '%SPP%';
```

```sql
   truncate table SPP_NOT_COM;
   truncate table  SPP_COM;

insert into SPP_COM
   select t.file_unique_id,t.mr_content from jhmr_file_content_log t ;
   insert into SPP_NOT_COM
   select t.file_unique_id,t.mr_content from jhmr_file_content_log t ;

select count(1) from SPP_COM;
   select count(1) from SPP_NOT_COM;

select * from SPP_COM;
   select * from SPP_NOT_COM;
```