Querying oracle clob column

Question

I have a table with a clob column. Searching based on the clob column content needs to be performed. However

select * from aTable where aClobColumn = \'value\';

Answer 1

So do not. Because if you want to compare the data - then it may be a situation where one value: NULL and the second EMPTY_CLOB And it is for this method different matter! It returns -1, although in terms of data - both values ​​should not contain. Would be correct:

dbms_lob.compare (NVL (AUDIT_PAYLOAD_TEXT_DEC, Empty_Clob ()),  NVL (AUDIT_PAYLOAD_TEXT, Empty_Clob ()))

Answer 2

Yes, it's not allowed (this restriction does not affect CLOBs comparison in PL/SQL) to use comparison operators like =, !=, <> and so on in SQL statements, when trying to compare two CLOB columns or CLOB column and a character literal, like you do. To be able to do such comparison in SQL statements, dbms_lob.compare() function can be used.

  select * 
    from aTable 
   where dbms_lob.compare(aClobColumn, 'value') = 0

In the above query, the 'value' literal will be implicitly converted to the CLOB data type. To avoid implicit conversion, the 'value' literal can be explicitly converted to the CLOB data type using TO_CLOB() function and then pass in to the compare() function:

  select * 
    from aTable 
   where dbms_lob.compare(aClobColumn, to_clob('value')) = 0

Answer 3

Clob's are large datatypes that can store massive data and hence many operators that support varchar operations will not work on Clob, but in PL/SQL some of them do like mentioned here: http://docs.oracle.com/cd/B19306_01/appdev.102/b14249/adlob_sql_semantics.htm#g1016221

As you can see in the table Like is supported in both Sql and pl/sql for clobs, but = is not supported in SQL, but is in pl/sql

If you really need to you could convert to varchar in sql and compare like Tom Kyte mentions here like this: http://sqlfiddle.com/#!4/1878f6/1

select * from aTable where dbms_lob.substr( aClobColumn , length(aClobColumn), 1 )='value';

Answer 4

how about

select * from table_name where to_char(clob_column) ="test_string"