Sql 读取oracle表中的BLOB列

我有一个表tbl，它有以下列：

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

当我运行下面的查询时，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')

这意味着（例外情况表明）列

ColLB

中不包含用于解压缩的有效值

测试表明，is很可能是一个带有

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，如果存储的非

NULL

值已损坏（即不是压缩格式），则会看到不同的异常

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

大小写

station测试

NULL

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 

---

嗨，Marmite，谢谢你的意见。是的，你是对的。另一个BLOB列可为null，因此引发了错误。我已经按照你的建议处理了。@PujaShaw，你很好！

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

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