On 02/08/2013 12:08 PM, Yongil Jang wrote:
Dear,
I'm trying to make a mystrstr function to use it as a sub-function of
"like".
mystrstr function is designed to use boyer-moore algorithm to improve
string search performance.
(Only for simple substing search, but not a complex search pattern)
But, the problem is occurred when this mystrstr function is called two more
times on one query.
In boyer-moore algorithm, search pattern string should be preprocessed
before it is used.
I used sqlite3_set_auxdata() and sqlite3_get_auxdata() function to save
preprocessed search pattern to call preprocessing process only once.
It works very well if I use only one mystrstr function on one query.
example)
select * from mytable where mystrstr(col1, 'test1') and mystrstr(col2,
'test2');
In this case, mystrstr function is called twice and there are two different
search patterns.
I can use two aux data slots and can find preprocessed patterns by string
compare with original pattern string for each call of mystrstr().
But, I think it is not a good idea, because of string compare can make not
necessary processing cost.
I don't think you should have to do anything special for this to work.
SQLite will allocate separate aux-data slots to each invocation. The
array of aux-data slots accessed by "mystrstr(col1, 'test1')" is
different to the array accessed by "mystrstr(col2, 'test2')". So if
the implementation just stores the compiled version of the search
pattern in aux-data slot 1 things should just work.
Dan.
Could I get some more information of currently called function?
For example, If I can get PC(program count of VDBE) from context, this
value can be used to distinguish current position of my function on a query.
Thank you.
Yongil Jang.
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