oracle - Searching first condition first and only if not available then second condition -

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i writing sql query query should first search first value, , if value missing query should search second value.

i have 2 tables. 1 of these tables contains modification date (this not filled , can null) , creation date filled.

now want query first looks in table modification date , if null looks @ table creation date.

example of query:

select *   all_articles   to_char(modification_date, 'yyyymmdd') = to_char(sysdate, 'yyyymmdd')-1  -- if empty record   to_char(creation_date, 'yyyymmdd') = to_char(sysdate, 'yyyymmdd')-1

can me query?

almost major rdbms' available have in built functions handle such situation. oracle db has nvl function works follows: nvl(modified_dt, create_dt);

the above return modified_dt column data default. however, if isn't available, return create_dt.

see here details: http://www.w3schools.com/sql/sql_isnull.asp


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