Consider the following table
select * from my_table
NAME
----
FAHD
FAHD_SHARIFF
SHARIFF_FAHD
FAHDSHARIFF
If you want to select only those names containing an underscore, the following query will NOT work:
select * from my_table where name like '%_%'
NAME
----
FAHD
FAHD_SHARIFF
SHARIFF_FAHD
FAHDSHARIFF
All rows are returned even though rows 1 and 4 do not contain an underscore! This is because an underscore is a special character - it is a single character wildcard.
You need to escape the underscore so that Oracle treats it as a literal:
select * from my_table where name like '%\_%' escape '\'
NAME
----
FAHD_SHARIFF
SHARIFF_FAHD
