In this post, I am sharing an example of applying Full Text Search on PostgreSQL Table with Index.

Here, I am using tsvector for full text search which is document type and uses match operator like @@.

PostgreSQL: Example of Trigram Index for Full Text Search using pg_trgm Extension

Below is an example:

Create a sample table with data:

CREATE TABLE tbl_Textdata
(id int, txt character varying);

INSERT INTO tbl_Textdata VALUES
(1,'I am DBA'),(2,'database research & development'),(3,'think for data only')
,(4,'data is important'),(5,'data is a future'),(6,'I am data owner');

Do Full Text Searching:

SELECT txt
FROM tbl_Textdata
WHERE to_tsvector(txt) @@ to_tsquery('data');

Result:

txt
--------------------------
'think for data only'
'data is important'
'data is a future'
'I am data owner'

Apply an Index on require Text Pattern:

CREATE INDEX tbl_Textdata_txt_idx ON tbl_Textdata USING GIN (to_tsvector('english',txt));

Check the execution plan:

explain analyze
SELECT txt
FROM tbl_Textdata
WHERE to_tsvector(txt) @@ to_tsquery('data');

'Seq Scan on tbl_textdata  (cost=0.00..4.07 rows=1 width=32) (actual time=0.043..0.058 rows=4 loops=1)'
'  Filter: (to_tsvector((txt)::text) @@ to_tsquery('data'::text))'
'  Rows Removed by Filter: 2'
'Planning time: 5.494 ms'
'Execution time: 0.083 ms'

In this post, I am sharing few examples of full text searching and pattern matching in PostgreSQL.
PostgreSQL provides the different options for Full text searching and pattern matching.

Here, I am using tsvector for full text search which is document type and uses match operator like @@.

PostgreSQL: Example of Trigram Index for Full Text Search using pg_trgm Extension

Below are the few examples of Full Text Search:

Casting in tsvector:

SELECT 'I am owner of dbrnd.com'::tsvector @@ 'am & of'::tsquery as Result

result 
---------
true


SELECT 'I am owner of dbrnd.com'::tsvector @@ 'am & dbrnd.com'::tsquery as Result

result 
---------
true

SELECT 'I am owner of dbrnd.com'::tsvector @@ 'am & dbrnd'::tsquery as Result

result 
---------
false

Use to_tsvector():

SELECT to_tsvector('I am owner of dbrnd.com') @@ to_tsquery('owner & dbrnd.com') as Result

result 
---------
true

Search adjacent string combination:

SELECT to_tsvector('anvesh patel') @@ to_tsquery('anvesh <-> patel') as Result

result 
---------
true

SELECT to_tsvector('anvesh m patel') @@ to_tsquery('anvesh <-> patel') as Result

result 
---------
false

SELECT to_tsvector('anvesh m patel') @@ to_tsquery('anvesh <2> patel') as Result

result 
---------
true

In this post, I am sharing the use of CONTAINS for matching the patterns in SQL Server.

We know about the LIKE predicate which we are using for a specific type of pattern matching. SQL Server Full-Text Search Index stores the different patterns of the defined column.

We can employ CONTAINS on the column of Full-Text Search and can search different patterns.

Please check the below demonstrations:

Create a table with sample records:

CREATE TABLE tbl_Employee (empid int not null, ename varchar(20) not null, salary int)
GO

INSERT INTO tbl_Employee VALUES 
(1,'abc',25000),(2,'xyz',30000),(3,'svq',40000)
,(4,'cvq',26000),(5,'rfq',70000),(6,'opq',45000)
GO

Create a Full Text Search Index:

CREATE UNIQUE INDEX uk_empid ON tbl_Employee(empid);
  
CREATE FULLTEXT CATALOG ft AS DEFAULT; 

CREATE FULLTEXT INDEX ON tbl_Employee(ename)   
   KEY INDEX uk_empid   
   WITH STOPLIST = SYSTEM;

Use CONTAINS, for performing FULL Text Search:
Check the below sample use of CONTAINS, If you want to use the same thing using LIKE then we have to write LIKE separately for each pattern.

SELECT *FROM [dbo].[tbl_Employee]
WHERE CONTAINS(ename, '"a*" OR "s*" OR "cv*"')

Result:

empid       ename                salary
----------- -------------------- -----------
1           abc                  25000
3           svq                  40000
4           cvq                  26000

In the PostgreSQL, we can use Trigram to enhance the use of Full Text Search.
The Trigram algorithm divides string like “dog” = “d”,”do”,”dog”,”og”.

The Trigram matching comes with pg_trgm extension.
We can also apply Trigram operators on Gist and GIN indexes which increase the search speed and enhance the performance.

We have already different thesaurus or synomyms for the Full Text Search, but we can use Trigram for implementing typing corrections and suggestions.

Here, you can find different examples of this.

Create a sample table:

CREATE TABLE tbl_TestTriGramIndex
(
	ID INT
	,TextData TEXT
);

Create a Trigram Index on Text Column:

CREATE INDEX trgm_idx_tbl_TestTriGramIndex_TextData ON tbl_TestTriGramIndex USING GIST (TextData gist_trgm_ops);

If you get below error, install require pg_trgm extension:

ERROR:  operator class "gist_trgm_ops" does not exist for access method "gist"

Install pg_trgm extension:

CREATE EXTENSION pg_trgm;

Insert few sample records:

INSERT INTO tbl_TestTriGramIndex
VALUES 
(1,'Anvesh Patel')
,(2,'Database Research & Development')
,(3,'PostgreSQL is better than SQL Server')
,(4,'PostgreSQL is supported powerful BRIN Indexes');

Execute few SELECTs for text comparison:

SELECT *FROM tbl_TestTriGramIndex
WHERE TextData % 'PostgreSQL is';

SELECT *FROM tbl_TestTriGramIndex
WHERE TextData LIKE '%SQL%';

SELECT *FROM tbl_TestTriGramIndex
WHERE TextData ~* 'ql';

Execute below SELECTs and check Trigram generated result of given string:

SELECT SHOW_TRGM('Anvesh') AS Anvesh;
SELECT SHOW_TRGM('Anvesh Patel') AS AnveshPatel;

Execute below SELECTs and check percentage of similarity:

SELECT SIMILARITY('Anvesh','anv') AS SimilarPercentage;
SELECT SIMILARITY('Anvesh','anve') AS SimilarPercentage;