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Oracle Escape Characters

Oracle Tips by Burleson Consulting

 

Oracle allows the assignment of special escape characters to tell Oracle that the character is interpreted literally.  Certain characters such as the underscore ?_? are not interpreted literally because they have special meaning within Oracle.

In the example below, we want to find all Oracle parameter that relate to I/O, so we are tempted to use the filter LIKE  ?%_io_%?.  Below we will select from the x$ksppi fixed table, filtering with the LIKE clause:

select ksppinm
from x$ksppi
where ksppinm like '%_io_%';

 

KSPPINM                                                                        

--------------------------------           

sessions                                                                        

license_max_sessions                                                           

license_sessions_warning                                                       

_session_idle_bit_latches                                                       

_enable_NUMA_optimization                                                      

java_soft_sessionspace_limit                                                   

java_max_sessionspace_size                                                     

_trace_options                                                                 

_io_slaves_disabled                                                            

dbwr_io_slaves                                                                 

_lgwr_io_slaves

As you can see above, we did not get the answer we expected.  The SQL displayed all values that contained ?io?, and not just those with an underscore.  To remedy this problem, Oracle SQL supports an ESCAPE clause to tell Oracle that the character is to be interpreted literally:

select ksppinm
from x$ksppi
where ksppinm like '%\_io\_%' ESCAPE '\';

 

KSPPINM                                                                        

--------------------------------------           

_io_slaves_disabled                                                            

dbwr_io_slaves                                                                 

_lgwr_io_slaves                                                                

_arch_io_slaves                                                                

_backup_disk_io_slaves                                                         

backup_tape_io_slaves                                                          

_backup_io_pool_size                                                            

_db_file_direct_io_count                                                       

_log_io_size                                                                   

fast_start_io_target                                                            

_hash_multiblock_io_count                                                      

_smm_auto_min_io_size                                                          

_smm_auto_max_io_size                                                           

_ldr_io_size 

 

This is an excerpt from the book Oracle 10g Grid & Real Application Clusters -
Oracle10g Grid Computing with RAC.
 



 

 

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