Perform case-insensitive search in Oracle database
Comparison operators (such as LIKE, =, etc.) in Oracle database are case-sensitive by default. This can present a challenge when you need to search data without regard to case. To solve this problem, Oracle provides several ways to perform case-insensitive searches without relying on full-text indexes.
Method 1: Case conversion
You can use the UPPER() or LOWER() function to force all data to be in the same case. For example:
select * from my_table where upper(column_1) = upper('my_string');
or
select * from my_table where lower(column_1) = lower('my_string');
This may require a full table scan if column_1
is not indexed on upper(column_1)
or lower(column_1)
respectively. To avoid this, create a function-based index:
create index my_index on my_table ( lower(column_1) );
For the LIKE operator, add % around the search string:
select * from my_table where lower(column_1) LIKE lower('my_string') || '%';
Method 2: Regular expression
The REGEXP_LIKE() function introduced starting with Oracle 10g provides case-insensitive search by specifying the 'i' match parameter:
select * from my_table where regexp_like(column_1, '^my_string$', 'i');
To use this as an equality operator, specify the beginning and end of the string (using ^ and $):
select * from my_table where regexp_like(column_1, '^my_string$', 'i');
For LIKE equivalent search, remove ^ and $. Note that the search string may contain characters that are interpreted differently by the regular expression engine.
Method 3: Session-level configuration
The NLS_SORT parameter defines the sort order of comparisons, including = and LIKE. You can enable case-insensitive sorting for all queries in a session by setting it to BINARY_CI:
alter session set nls_sort=BINARY_CI;
You may also want to set NLS_COMP to LINGUISTIC to force language comparison:
alter session set nls_comp=LINGUISTIC;
To improve performance, you can create a language index:
create index my_linguistc_index on my_table (NLSSORT(column_1, 'NLS_SORT = BINARY_CI'));
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