Select LIKE '%string%', without FULL-TEXT-SEARCH in SQL Server - sql

Question

-- create table
CREATE TABLE dbo.Tests
(
Id BIGINT NOT NULL IDENTITY,
String NVARCHAR(100),
StringReversed AS REVERSE(String),
CONSTRAINT PK_Tests PRIMARY KEY (Id),
)
CREATE NONCLUSTERED INDEX IX1 ON dbo.Tests(String)
CREATE NONCLUSTERED INDEX IX2 ON dbo.Tests(StringReversed)
-- populate table with 100k random strings (for testing)
DECLARE #I INT = 100000
WHILE #I > 0
BEGIN
INSERT INTO Tests(String)
SELECT CONVERT(varchar(36), NEWID())
SET #I = #I - 1
END
-- how do i do a LIKE '%STRING%' search which uses the index?
SELECT String, StringReversed FROM Tests WHERE String LIKE '%0A7EB%'
SELECT String, StringReversed FROM Tests
WHERE String LIKE '0A7EB%' OR StringReversed LIKE 'BE7A0%'
Can you help me with this? I am trying to implement a full-text-search alternative to be able to do a LIKE '%STRING%' WHERE clause.
I'm stuck not quite sure if this is even possible to implement? Let's just assume that FULL TEXT SEARCH is not possible, and I need to use index.
This is a prod issue and we need to do a LIKE '%search%' in the string column. I just read here: SQL Server: Index columns used in like? that we can do a reverse?
Hope you can help me, thanks a lot.

Answer 1

Update: I tried the string fragments approach.
-- create table
CREATE TABLE dbo.Tests
(
Id BIGINT NOT NULL IDENTITY,
String NVARCHAR(100),
CONSTRAINT PK_Tests PRIMARY KEY (Id),
)
GO
-- create table for Test String Fragments
CREATE TABLE dbo.TestStringFragments(
Id BIGINT NOT NULL IDENTITY,
TestId BIGINT NOT NULL,
Fragment NVARCHAR(100),
CONSTRAINT PK_TestStringFragments PRIMARY KEY (Id)
)
CREATE NONCLUSTERED INDEX IX_TestStringFragments_Fragment ON dbo.TestStringFragments(Fragment)
CREATE NONCLUSTERED INDEX IX_TestStringFragments_TestId ON dbo.TestStringFragments(TestId)
GO
-- create UDF to generate string fragments
CREATE FUNCTION dbo.CreateStringFragments(#input nvarchar(100))
RETURNS TABLE WITH SCHEMABINDING
AS
RETURN
(
WITH x(x) AS
(SELECT 1 UNION ALL SELECT x+1 FROM x WHERE x < (LEN(#input)))
SELECT Fragment = SUBSTRING(#input, x, LEN(#input)) FROM x
)
GO
-- create trigger for the Tests table
CREATE TRIGGER dbo.Tests_MaintainStringFragments
ON dbo.Tests
FOR INSERT, UPDATE, DELETE
AS
BEGIN
SET NOCOUNT ON
DELETE TSF FROM dbo.TestStringFragments AS TSF
INNER JOIN deleted ON TSF.TestId = deleted.Id
INSERT dbo.TestStringFragments(TestId, Fragment)
SELECT inserted.Id, fragments.Fragment
FROM inserted
CROSS APPLY dbo.CreateStringFragments(inserted.String) AS fragments
END
GO
-- populate table with 100k random strings (for testing)
DECLARE #I INT = 100000
WHILE #I > 0
BEGIN
INSERT INTO Tests(String)
SELECT CONVERT(varchar(36), NEWID())
SET #I = #I - 1
END
Able to replicate the LIKE '%string%' code via the fragments table.
SELECT T.* FROM Tests T WITH(NOLOCK)
WHERE T.String LIKE '%CBB2%'
SELECT T.* FROM Tests T WITH(NOLOCK)
INNER JOIN TestStringFragments TSF WITH(NOLOCK) ON T.Id = TSF.TestId
where TSF.Fragment LIKE 'CBB2%'
My new execution plan is 61% for the first query, 39% for the second one. I'll check the trigrams approach.