Informix SQL文本Blob通配符搜索

Question

I am looking for an efficient way to use a wild card search on a text (blob) column.
I have seen that it is internally stored as bytes... The data amount will be limited, but unfortunately my vendor has decided to use this stupid datatype. I would also consider to move everything in a temp table if there is an easy system side function to modify it - unfortunately something like rpad does not work...
I can see the text value correctly via using the column in the select part or when reading the data via Perl's DBI module.

Answer 1

Unfortunately, you are stuck - there are very few operations that you can perform on TEXT or BYTE blobs. In particular, none of these work:

+ create table t (t text in table);
+ select t from t where t[1,3] = "abc";
SQL -615: Blobs are not allowed in this expression.
+ select t from t where t like "%abc%";
SQL -219: Wildcard matching may not be used with non-character types.
+ select t from t where t matches "*abc*";
SQL -219: Wildcard matching may not be used with non-character types.

Depending on the version of IDS, you may have options with BTS - Basic Text Search (requires IDS v11), or with other text search data blades. On the other hand, if the data is already in the DB and cannot be type-converted, then you may be forced to extract the blobs and search them client-side, which is less efficient. If you must do that, ensure you filter on as many other conditions as possible to minimize the traffic that is needed.

You might also notice that DBD::Informix has to go through some machinations to make blobs appear to work - machinations that it should not, quite frankly, have to go through. So far, in a decade of trying, I've not persuaded people that these things need fixing.