How to pickup date from long string Name column in oracle - mysql

Question

I have table with column 'ID', 'File_Name'
Table
ID File_Name
123 ROSE1234_LLDAtIInstance_03012014_04292014_190038.zip
456 ROSE1234_LLDAtIInstance_08012014_04292014_190038.zip
All I need is to pickup the first date given in file name.
Required:
ID Date
123 03012014
456 08012014

Answer 1

Here's one method assuming 8 characters after 2nd _ is always true.
It finds the position of the first _ then looks for the position of the 2nd _ using the position of the first _+1 then it looks for the 8 characters after the 2nd _
SELECT Id
, substr(File_name, instr(File_name,'_',instr(File_name,'_')+1)+1,8) as Date
FROM Table
or
a more elegant way would be to use a RegExp_Instr Function which eliminates the need for nesting instr.
SELECT Id, substr(File_name,REGEXP_INSTR(FileName,'_',1,2)+1,8) as date
FROM dual;

Answer 2

Why don't you simply put the date in separate column? E.g. you can than query the (indexed) date. The theory says the date is a property of the file. It's about avoiding errors, maintainability and so on. What in the zip files? Excel sheets I suppose :-)

Answer 3

Use a much simplified call to REGEXP_SUBSTR( ):
SQL> with tbl(ID, File_name) as (
2 select 123, 'ROSE1234_LLDAtIInstance_03012014_04292014_190038.zip' from dual
3 union
4 select 456, 'ROSE1234_LLDAtIInstance_08012014_04292014_190038.zip' from dual
5 )
6 select ID,
7 REGEXP_SUBSTR(File_name, '_(\d{8})_', 1, 1, NULL, 1) "Date"
8 from tbl;
ID Date
---------- ----------------------------------------------------
123 03012014
456 08012014
SQL>
For 11g, click here for the parameters to REGEXP_SUBSTR( ).
EDIT: Making this a virtual column would be another way to handle it. Thanks to Epicurist's post for the idea. The virtual column will contain a date value holding the filename date once the ID and filename are committed. Add it like this:
alter table X_TEST add (filedate date generated always as (TO_DATE(REGEXP_SUBSTR(Filename, '_(\d{8})_', 1, 1, NULL, 1), 'MMDDYYYY')) virtual);
So now just insert the ID and Filename, commit and there's your filedate. Note that its read-only.