@@ match operator in PostgreSQL

Introduction

The @@ operator helps you quickly find rows where text matches a search query using full-text search.

You want to search for articles containing certain words.

You need to filter products by keywords in descriptions.

You want to find customer feedback mentioning specific topics.

You want to build a search feature that ranks results by relevance.

Syntax

PostgreSQL

tsvector_column @@ to_tsquery('search_query')

tsvector_column holds searchable text in a special format.

to_tsquery('search_query') converts your search words into a query format.

Examples

Find rows where both 'cat' and 'dog' appear.

PostgreSQL

content_vector @@ to_tsquery('cat & dog')

Find rows where either 'cat' or 'dog' appear.

PostgreSQL

content_vector @@ to_tsquery('cat | dog')

Find rows with words starting with 'cat', like 'cats' or 'category'.

PostgreSQL

content_vector @@ to_tsquery('cat:*')

Sample Program

This creates a table with articles, stores searchable text in content_vector, inserts three articles, then finds articles mentioning 'dog'.

PostgreSQL

CREATE TABLE articles (
  id SERIAL PRIMARY KEY,
  title TEXT,
  body TEXT,
  content_vector tsvector
);

INSERT INTO articles (title, body, content_vector) VALUES
('Cats and Dogs', 'Cats and dogs are common pets.', to_tsvector('Cats and dogs are common pets.')),
('Bird Watching', 'Birds are beautiful creatures.', to_tsvector('Birds are beautiful creatures.')),
('Dog Training', 'Training your dog is important.', to_tsvector('Training your dog is important.'));

SELECT id, title FROM articles WHERE content_vector @@ to_tsquery('dog');

Important Notes

Make sure to update the tsvector column when text changes.

The @@ operator is fast when you create an index on the tsvector column.

Summary

The @@ operator matches text columns against search queries.

Use to_tsquery() to build your search terms.

This helps build powerful text search features in PostgreSQL.

Practice

1.

What does the @@ operator do in PostgreSQL?

easy

A. It concatenates two text strings.

B. It compares two numeric values for equality.

C. It matches a text column against a full-text search query.

D. It checks if a value is NULL.

Solution

1. Step 1: Understand the purpose of @@ operator

   The @@ operator is used in PostgreSQL for full-text search to match text columns against search queries.

2. Step 2: Compare with other options

   Other options describe unrelated operations like numeric comparison, string concatenation, or NULL checks, which are not related to @@.

3. Final Answer:

   It matches a text column against a full-text search query. -> Option C

4. Quick Check:

   @@ = full-text match [OK]

Hint: Remember: @@ is for full-text search matching [OK]

Common Mistakes:

• Confusing @@ with equality operator =
• Thinking @@ concatenates strings
• Assuming @@ checks for NULL

2.

Which of the following is the correct syntax to use the @@ operator with to_tsquery in PostgreSQL?

SELECT * FROM articles WHERE content @@ to_tsquery('search_term');

easy

A. SELECT * FROM articles WHERE content @@ to_tsquery('search_term');

B. SELECT * FROM articles WHERE content = to_tsquery('search_term');

C. SELECT * FROM articles WHERE content @@ 'search_term';

D. SELECT * FROM articles WHERE content LIKE to_tsquery('search_term');

Solution

1. Step 1: Identify correct usage of @@ with to_tsquery

   The @@ operator requires the right side to be a tsquery, which is created by to_tsquery().

2. Step 2: Check each option

   SELECT * FROM articles WHERE content @@ to_tsquery('search_term'); correctly uses content @@ to_tsquery('search_term'). Options B, C, and D misuse operators or omit to_tsquery().

3. Final Answer:

   SELECT * FROM articles WHERE content @@ to_tsquery('search_term'); -> Option A

4. Quick Check:

   Use @@ to_tsquery() syntax [OK]

Hint: Always use to_tsquery() on right side of @@ [OK]

Common Mistakes:

• Using = instead of @@
• Passing plain string without to_tsquery()
• Using LIKE operator for full-text search

3.

Given the table documents with a text_content column, what will this query return?

SELECT id FROM documents WHERE text_content @@ to_tsquery('cat & dog');

Assuming the table has these rows:

• 1: 'The cat chased the dog.'
• 2: 'A dog and a cat are friends.'
• 3: 'The cat is sleeping.'

medium

A. []

B. [1, 2]

C. [3]

D. [1, 2, 3]

Solution

1. Step 1: Understand the query condition

   The query uses to_tsquery('cat & dog'), which means both 'cat' AND 'dog' must be present in text_content.

2. Step 2: Check each row for both words

   Row 1 has 'cat' and 'dog'. Row 2 has both words as well. Row 3 only has 'cat', missing 'dog'.

3. Final Answer:

   [1, 2] -> Option B

4. Quick Check:

   AND search returns rows with both terms [OK]

Hint: Use & in to_tsquery for AND condition [OK]

Common Mistakes:

• Assuming OR instead of AND with &
• Expecting rows missing one word to match
• Confusing to_tsquery syntax

4.

Identify the error in this query:

SELECT * FROM posts WHERE content @@ 'cat | dog';

medium

A. content column cannot be used with @@ operator.

B. Incorrect use of the | operator inside the string.

C. The query should use LIKE instead of @@.

D. Missing to_tsquery() function around the search string.

Solution

1. Step 1: Check the right side of @@ operator

   The right side must be a tsquery type, usually created by to_tsquery(). Here, it's a plain string.

2. Step 2: Identify the missing function

   The query should be content @@ to_tsquery('cat | dog') to be valid.

3. Final Answer:

   Missing to_tsquery() function around the search string. -> Option D

4. Quick Check:

   Right side of @@ needs to_tsquery() [OK]

Hint: Always wrap search terms with to_tsquery() [OK]

Common Mistakes:

• Using plain string without to_tsquery()
• Thinking | operator is invalid inside to_tsquery
• Confusing @@ with LIKE

5.

You want to find all rows in messages where the body contains either 'error' or 'failure' but not both. Which to_tsquery expression with @@ operator will achieve this?

hard

A. body @@ to_tsquery('(error | failure) & !(error & failure)')

B. body @@ to_tsquery('error | failure & !error & !failure')

C. body @@ to_tsquery('error <-> failure')

D. body @@ to_tsquery('error | failure')

Solution

1. Step 1: Understand the requirement

   We want rows containing 'error' or 'failure' but NOT both. This is an exclusive OR (XOR) condition.

2. Step 2: Analyze the options

   body @@ to_tsquery('(error | failure) & !(error & failure)') uses (error | failure) & !(error & failure), which means 'error or failure' AND NOT 'both error and failure'. This matches XOR logic.

3. Step 3: Check other options

   body @@ to_tsquery('error | failure & !error & !failure') is invalid syntax. body @@ to_tsquery('error | failure') matches any with 'error' or 'failure' including both. body @@ to_tsquery('error <-> failure') looks for 'error' immediately followed by 'failure'.

4. Final Answer:

   body @@ to_tsquery('(error | failure) & !(error & failure)') -> Option A

5. Quick Check:

   XOR = (A OR B) AND NOT (A AND B) [OK]

Hint: Use (A | B) & !(A & B) for XOR in to_tsquery [OK]

Common Mistakes:

• Using simple OR instead of XOR
• Incorrect syntax for NOT operator
• Confusing proximity operator <-> with XOR