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[Andrey Zhakov <andrey.zhakov@xxxxxxxxx>]

Hi Arjen,

> --- On Thu, 23 Oct 2008, Arjen Lentz <arjen@xxxxxxxxxxxxxxxx> wrote:
> Hi Andrey

> On 23/10/2008, at 4:10 AM, Andrey Zhakov wrote:

>> MATCH is a complex feature itself. IMO, mixing up MATCH with virtual  
>> columns is over-complication. I want to keep things as simple as  
>> possible but if you know how a potential customer could benefit from  
>> that (I intentionally added the TODO comment to raise a discussion)  
>> then please let me know..
>
> Hehe - smart fella ;-)
> Can you describe what a MATCH-based virtual column is/does?

MATCH-based virtual columns are virtual columns whose function expression contains the keyword MATCH.
E.g. For table articles in http://dev.mysql.com/doc/refman/5.1/en/fulltext-natural-language.html a vcol might be created as follows:
vcol_name VIRTUAL DOUBLE AS (match(title,body) against ('database' in natural language mode))

MATCH returns the DOUBLE-type relevance of the found record according to the searched result.

In general virtual columns can be used to:
1) Simplify frequently used SELECT's
So instead of 
   select title,body,
          match(title,body) against ('database' in natural language mode) as relevance
   from articles
   where match (title,body) against ('database' in natural language mode)
   having relevance > 0.5

you could write

   select title,body,vcol_field
   from articles
   where vcol_field > 0.5

2) Define a functional index.
3) Use them instead of BEFORE INSERT triggers to speed up inserts
4) Use them instead of BEFORE INSERT triggers to ensure the values are always re-calculated when the vcol expression is altered.
5) Any other?..

Honestly I am not sure about any potential use case for MATCH-based  virtual columns.
I also think that the effort to re-enable MATCH in my patch in not that big so I would not like to spend too much time on discussions...

Cheers,
Andrey.



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