Searchable text is in 2 tables, how to design full text index? - sql-server

Question

In a forum application, the actual name of the thread is stored in a table, and then replies is stored in another table.
Table_Thread
Subject varchar(255) e.g. "How to setup fulltext search"
Table_Replies (users replies here)
ReplyText text(not null)
Now I want to create a full-text search on both the subject and reply columns, but they seem very related so they should be in the same index.
Is it possible to do this?
I'm using sql server 2005.

Answer 1

Assuming there is an association between the subject and the replies you could create a view WITH SCHEMABINDING, create a UNIQUE CLUSTERED index on the view and then add that view to your fulltext catalog selecting the two columns you want included.

Answer 2

When huge concurrent query requests come, RDBMS cannot afford it by SQL. what's more, select SQL supports full-text search badly. So you need IR (Information Retrieval) library such as Lucene for java.

Answer 3

You could create a indexed view containing an union of both indexed columns + PK of the tables
e.g.
CREATE VIEW SearchText
WITH SCHEMABINDING
AS SELECT * FROM (
(Subject as Text, Table_Thread_ID as ID, 1 as Type FROM Table_Thread)
UNION ALL
(ReplyText as Text, Table_Replies_ID as ID, 2 as Type FROM Table_Replies));
I put type 1 and 2 as arbitrary, since you need a unique key to build a fulltext index.
And then create a unique index on (ID, Type), and finally your fulltext index.
CREATE UNIQUE INDEX SearchText_UK ON SearchText (ID, Type);
CREATE FULLTEXT CATALOG ft AS DEFAULT;
CREATE FULLTEXT INDEX ON SearchText(Text)
KEY INDEX SearchText_UK
WITH STOPLIST = SYSTEM;

Answer 4

I have seen what NopCommerce (C# MVC Open Source E-Commerce) has done using fulltext search on 'products' and 'variants' and only return 'products'. This is very similar to your case because you want to search on 'Thread' and 'Replies' but you obviously want to only return 'threads'. I have change it to use threads and replies for you:
First, create a function that generates an index name by table (optional):
CREATE FUNCTION [dbo].[nop_getprimarykey_indexname]
(
#table_name nvarchar(1000) = null
)
RETURNS nvarchar(1000)
AS
BEGIN
DECLARE #index_name nvarchar(1000)
SELECT #index_name = i.name
FROM sys.tables AS tbl
INNER JOIN sys.indexes AS i ON (i.index_id > 0 and i.is_hypothetical = 0) AND (i.object_id=tbl.object_id)
WHERE (i.is_unique=1 and i.is_disabled=0) and (tbl.name=#table_name)
RETURN #index_name
END
GO
Then, enable fulltext by creating the catalog and the indexes:
EXEC('
IF NOT EXISTS (SELECT 1 FROM sys.fulltext_catalogs WHERE [name] = ''myFullTextCatalog'')
CREATE FULLTEXT CATALOG [myFullTextCatalog] AS DEFAULT')
DECLARE #create_index_text nvarchar(4000)
SET #create_index_text = '
IF NOT EXISTS (SELECT 1 FROM sys.fulltext_indexes WHERE object_id = object_id(''[Table_Thread]''))
CREATE FULLTEXT INDEX ON [Table_Thread]([Subject])
KEY INDEX [' + dbo.[nop_getprimarykey_indexname] ('Table_Thread') + '] ON [myFullTextCatalog] WITH CHANGE_TRACKING AUTO'
EXEC(#create_index_text)
SET #create_index_text = '
IF NOT EXISTS (SELECT 1 FROM sys.fulltext_indexes WHERE object_id = object_id(''[Table_Replies]''))
CREATE FULLTEXT INDEX ON [Table_Replies]([ReplyText])
KEY INDEX [' + dbo.[nop_getprimarykey_indexname] ('Table_Replies') + '] ON [myFullTextCatalog] WITH CHANGE_TRACKING AUTO'
EXEC(#create_index_text)
Then, in the stored procedure to obtain products by keywords, build a temporary table with a list of product Ids that match the keywords.
INSERT INTO #KeywordThreads ([ThreadId])
SELECT t.Id
FROM Table_Thread t with (NOLOCK)
WHERE CONTAINS(t.[Subject], #Keywords)
UNION
SELECT r.ThreadId
FROM Table_Replies r with (NOLOCK)
WHERE CONTAINS(pv.[ReplyText], #Keywords)
Now you can use the temporary table #KeywordThreads to join with the list of threads and return them.
I hope this helps.