Using LIKE in an Oracle IN clause

问题:

I know I can write a query that will return all rows that contain any number of values in a given column, like so:

Select * from tbl where my_col in (val1, val2, val3,... valn)

but if val1, for example, can appear anywhere in my_col, which has datatype varchar(300), I might instead write:

select * from tbl where my_col LIKE '%val1%'

Is there a way of combing these two techniques. I need to search for some 30 possible values that may appear anywhere in the free-form text of the column.

Combining these two statements in the following ways does not seem to work:

select * from tbl where my_col LIKE ('%val1%', '%val2%', 'val3%',....) 

select * from tbl where my_col in ('%val1%', '%val2%', 'val3%',....)

回答1:

select * from tbl 
where my_col like '%val1%' or my_col like'%val2%' or my_col like '%val3%', ...

But beware, that might be quite slow... Alternatively, you could insert all acceptable values (including % signs) into a table and semi-join that table:

select * from tbl
where exists (select 1 from all_likes where tbl.my_col like all_likes.value)

For true full-text search, you might want to look at Oracle Text:

http://www.oracle.com/technetwork/database/enterprise-edition/index-098492.html

回答2:

No, you cannot do this. The values in the IN clause must be exact matches. You could modify the select thusly:

SELECT *
  FROM tbl
 WHERE my_col LIKE %val1%
    OR my_col LIKE %val2%
    OR my_col LIKE %val3%
 ...

If the val1, val2, val3... are similar enough, you might be able to use regular expressions in the REGEXP_LIKE operator.

回答3:

A REGEXP_LIKE will do a case-insensitive regexp search.

select * from Users where Regexp_Like (User_Name, 'karl|anders|leif','i')

This will be executed as a full table scan - just as the LIKE or solution, so the performance will be really bad if the table is not small. If it's not used often at all, it might be ok.

If you need some kind of performance, you will need Oracle Text (or some external indexer).

To get substring indexing with Oracle Text you will need a CONTEXT index. It's a bit involved as it's made for indexing large documents and text using a lot of smarts. If you have particular needs, such as substring searches in numbers and all words (including "the" "an" "a", spaces, etc) , you need to create custom lexers to remove some of the smart stuff...

If you insert a lot of data, Oracle Text will not make things faster, especially if you need the index to be updated within the transactions and not periodically.

回答4:

Yes, you can use this query:

  SELECT * FROM RandomTable rt 
    WHERE EXISTS (select 1 from table(sys.dbms_debug_vc2coll(//INSERT STRINGS SEPARATED BY COMMA HERE)) as MemoryTable mt where rt.name like mt.column_value);

This way you don't have to create a table.

回答5:

Just to add on @Lukas Eder answer.

An improvement to avoid creating tables and inserting values (we could use select from dual and unpivot to achieve the same result "on the fly"):

with all_likes as  
(select * from 
    (select '%val1%' like_1, '%val2%' like_2, '%val3%' like_3, '%val4%' as like_4, '%val5%' as like_5 from dual)
    unpivot (
     united_columns for subquery_column in ("LIKE_1", "LIKE_2", "LIKE_3", "LIKE_4", "LIKE_5"))
  )
    select * from tbl
    where exists (select 1 from all_likes where tbl.my_col like all_likes.united_columns)

回答6:

I prefer this

WHERE CASE WHEN my_col LIKE '%val1%' THEN 1    
           WHEN my_col LIKE '%val2%' THEN 1
           WHEN my_col LIKE '%val3%' THEN 1
           ELSE 0
           END = 1

I'm not saying it's optimal but it works and it's easily understood. Most of my queries are adhoc used once so performance is generally not an issue for me.

回答7:

This one is pretty fast :

select * from listofvalue l 
inner join tbl on tbl.mycol like '%' || l.value || '%'

回答8:

select * from tbl
 where exists (select 1 from all_likes where all_likes.value = substr(tbl.my_col,0, length(tbl.my_col)))