读取 oracle 表中的 BLOB 列

Question

我有一个表 tbl，它有以下几列：

create table tbl (id number,
                  colA BLOB,
                  ColB BLOB,
                  Insert_time timestamp(0)
                  )

当我运行以下查询时，它工作正常：

select id,
substr(substr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.colA), 2000, 1) ),instr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.ColA), 2000, 1) ),'MeterReadingReasonCode',1),25),24,2) first
--substr(substr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.ColB), 2000, 1) ),instr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.ColB), 2000, 1) ),'MeterReadingTypeCode',1),23),22,2) second
from tbl 
where
tbl.INSERT_TIME >=  To_Date('04-01-2020 12:00:00 AM' ,'dd-mm-yyyy hh12:mi:ss AM')
and tbl.INSERT_TIME <=  To_Date('04-08-2020 11:00:00 PM' ,'dd-mm-yyyy hh12:mi:ss AM')

但是当我在下面运行时会抛出错误：

select id,
substr(substr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.colA), 2000, 1) ),instr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.ColA), 2000, 1) ),'MeterReadingReasonCode',1),25),24,2) first
substr(substr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.ColB), 2000, 1) ),instr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.ColB), 2000, 1) ),'MeterReadingTypeCode',1),23),22,2) second
from tbl 
where
tbl.INSERT_TIME >=  To_Date('04-01-2020 12:00:00 AM' ,'dd-mm-yyyy hh12:mi:ss AM')
and tbl.INSERT_TIME <=  To_Date('04-08-2020 11:00:00 PM' ,'dd-mm-yyyy hh12:mi:ss AM')

我的意思是说，如果我只选择 1 个 blob 列来读取，那么日期过滤器就可以正常工作。 但是当我在 where 子句中选择两个带有日期过滤器的 BLOB 列时，它会抛出以下错误：

ORA-29261: bad argument
ORA-06512: at "SYS.UTL_SYS_COMPRESS", line 60
ORA-06512: at "SYS.UTL_SYS_COMPRESS", line 230
ORA-06512: at "SYS.UTL_COMPRESS", line 89
29261. 00000 -  "bad argument"
*Cause:    A bad argument was passed to the PL/SQL API.
*Action:   Check the arguments passed to the PL/SQL API and retry the call.

Answer 1

这个简单的意思是（正如例外所暗示的那样）ColLB 列中包含的解压缩值无效。

测试表明这很可能是一个具有NULL 值的列 - 请参见下面的脚本。

create table tbl (ColB BLOB);
                  
insert into tbl ( colb)
values(null);

select  
   utl_compress.lz_uncompress(tbl.ColB)
from tbl  
;

ORA-29261: bad argument
ORA-06512: at "SYS.UTL_SYS_COMPRESS", line 56
ORA-06512: at "SYS.UTL_SYS_COMPRESS", line 226
ORA-06512: at "SYS.UTL_COMPRESS", line 89

请注意，如果您存储了一个已损坏的非 NULL 值（即不是压缩格式），您会看到不同的异常

insert into tbl ( colb)
values(HEXTORAW('cafe'));

select  
   utl_compress.lz_uncompress(tbl.ColB)
from tbl  
;

ORA-29294: A data error occurred during compression or uncompression.
ORA-06512: at "SYS.UTL_SYS_COMPRESS", line 56
ORA-06512: at "SYS.UTL_SYS_COMPRESS", line 226
ORA-06512: at "SYS.UTL_COMPRESS", line 89

因此，作为一种解决方法，您应该使用 CASE 语句测试 NULL 来保护您的表达式

select 
  case when colB is not NULL then 
    substr(substr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.ColB), 2000, 1) ),instr(utl_raw.cast_to_varchar2( dbms_lob.substr( utl_compress.lz_uncompress(tbl.ColB), 2000, 1) ),'MeterReadingTypeCode',1),23),22,2) 
  end as  second
from tbl