Search configuration and languages in PostgreSQL - Mini Project: Build & Apply

Search Configuration and Languages in PostgreSQL

📖 Scenario: You are building a simple text search feature for a library database. The library has books in different languages, and you want to configure the search to work well with English and French texts.

🎯 Goal: Create a PostgreSQL setup that defines a text search configuration for English and French languages, then use it to search book titles effectively.

📋 What You'll Learn

Create a table called books with columns id (integer) and title (text).

Insert three books with titles in English and French.

Create a text search configuration for English language.

Create a text search configuration for French language.

Write a query that uses the English text search configuration to find books matching a search term.

💡 Why This Matters

🌍 Real World

Libraries, bookstores, and content management systems often need to search text in multiple languages accurately.

💼 Career

Understanding text search configurations is important for database developers and backend engineers working on search features.

1

Create the books table and insert data

Create a table called books with columns id as integer and title as text. Insert these three rows exactly: (1, 'The Great Gatsby'), (2, 'Le Petit Prince'), and (3, 'Pride and Prejudice').

PostgreSQL

-- Create the books table and insert three rows
-- Your code here

Hint

Use CREATE TABLE to define the table and INSERT INTO to add the rows.

2

Create English and French text search configurations

Create a text search configuration called english_search based on the built-in english configuration. Also create a text search configuration called french_search based on the built-in french configuration.

PostgreSQL

CREATE TABLE books (
    id INTEGER,
    title TEXT
);

INSERT INTO books (id, title) VALUES
(1, 'The Great Gatsby'),
(2, 'Le Petit Prince'),
(3, 'Pride and Prejudice');

-- Create english_search and french_search configurations
-- Your code here

Hint

Use CREATE TEXT SEARCH CONFIGURATION with COPY = english or COPY = french to base on built-in configs.

3

Write a query using English text search configuration

Write a SELECT query to find all books where the title matches the search term 'great' using the english_search text search configuration. Use to_tsvector with english_search on title and to_tsquery with english_search on the search term.

PostgreSQL

CREATE TABLE books (
    id INTEGER,
    title TEXT
);

INSERT INTO books (id, title) VALUES
(1, 'The Great Gatsby'),
(2, 'Le Petit Prince'),
(3, 'Pride and Prejudice');

CREATE TEXT SEARCH CONFIGURATION english_search ( COPY = english );
CREATE TEXT SEARCH CONFIGURATION french_search ( COPY = french );

-- Write a SELECT query to find books matching 'great' using english_search
-- Your code here

Hint

Use to_tsvector and to_tsquery with the english_search configuration and the @@ operator to match.

4

Complete by creating a French search query

Write a SELECT query to find all books where the title matches the search term 'petit' using the french_search text search configuration. Use to_tsvector with french_search on title and to_tsquery with french_search on the search term.

PostgreSQL

CREATE TABLE books (
    id INTEGER,
    title TEXT
);

INSERT INTO books (id, title) VALUES
(1, 'The Great Gatsby'),
(2, 'Le Petit Prince'),
(3, 'Pride and Prejudice');

CREATE TEXT SEARCH CONFIGURATION english_search ( COPY = english );
CREATE TEXT SEARCH CONFIGURATION french_search ( COPY = french );

SELECT id, title
FROM books
WHERE to_tsvector('english_search', title) @@ to_tsquery('english_search', 'great');

-- Write a SELECT query to find books matching 'petit' using french_search
-- Your code here

Hint

Similar to the English query, but use french_search and the search term 'petit'.

Practice

1. What is the main purpose of a search configuration in PostgreSQL?

easy

A. To define how text is processed for full-text search in a specific language

B. To store user login information securely

C. To manage database connections and pooling

D. To backup and restore database data

Solution

1. Step 1: Understand search configuration role

   Search configurations tell PostgreSQL how to handle text for searching, especially for different languages.

2. Step 2: Compare options

   Options A, C, and D relate to security, connections, and backups, not text processing.

3. Final Answer:

   To define how text is processed for full-text search in a specific language -> Option A

4. Quick Check:

   Search configuration = text processing [OK]

Hint: Search configs define text processing rules for languages [OK]

Common Mistakes:

• Confusing search configuration with user or connection settings
• Thinking it manages backups or security
• Assuming it stores data instead of processing text

2. Which of the following is the correct syntax to create a new text search configuration named my_config based on the built-in english configuration?

easy

A. CREATE TEXT SEARCH CONFIGURATION my_config AS english;

B. CREATE TEXT SEARCH CONFIGURATION my_config FROM english;

C. CREATE TEXT SEARCH CONFIGURATION my_config ( COPY = english );

D. CREATE TEXT SEARCH CONFIGURATION my_config LIKE english;

Solution

1. Step 1: Recall correct CREATE syntax

   PostgreSQL uses CREATE TEXT SEARCH CONFIGURATION name ( COPY = existing_config ) to copy an existing config.

2. Step 2: Check options

   Only CREATE TEXT SEARCH CONFIGURATION my_config ( COPY = english ); uses the correct syntax with COPY = english. Others use invalid keywords.

3. Final Answer:

   CREATE TEXT SEARCH CONFIGURATION my_config ( COPY = english ); -> Option C

4. Quick Check:

   Use COPY = for cloning configs [OK]

Hint: Use COPY = existing_config to clone search configs [OK]

Common Mistakes:

• Using FROM or AS instead of COPY =
• Omitting parentheses around COPY clause
• Confusing syntax with table creation

3. Given the following SQL commands:

CREATE TEXT SEARCH CONFIGURATION my_english ( COPY = english );
ALTER TEXT SEARCH CONFIGURATION my_english
  ALTER MAPPING FOR asciiword, asciihword, hword_asciipart
  WITH simple;
SELECT to_tsvector('my_english', 'PostgreSQL is great!');

What is the output of the SELECT statement?

medium

A. 'postgresql':1 'great':3 'is':2 'simple':5

B. 'postgresql':1 'great':3 'is':2

C. 'postgresql':1 'great':3

D. Syntax error due to ALTER MAPPING

Solution

1. Step 1: Understand ALTER MAPPING effect

   The ALTER MAPPING changes how asciiword and related tokens are processed, using the simple dictionary which does not remove stop words.

2. Step 2: Analyze to_tsvector output

   The text 'PostgreSQL is great!' produces tokens: 'PostgreSQL' (pos 1, asciiword) -> 'postgresql':1; 'is' (pos 2, asciiword) -> 'is':2; 'great' (pos 3, asciiword) -> 'great':3. Simple indexes all without dropping stopwords. Matches 'postgresql':1 'great':3 'is':2.

3. Final Answer:

   'postgresql':1 'great':3 'is':2 -> Option B

4. Quick Check:

   Alter mapping changes dictionary used [OK]

Hint: ALTER MAPPING changes dictionary for word processing [OK]

Common Mistakes:

• Assuming stop words are always removed
• Confusing dictionary effects on stemming and stop words
• Expecting syntax error from ALTER MAPPING

4. You run the following command:

ALTER TEXT SEARCH CONFIGURATION my_config
  ALTER MAPPING FOR word WITH english_stem;

But you get an error: ERROR: dictionary "english_stem" does not exist
What is the most likely cause?

medium

A. The configuration name is reserved and cannot be changed

B. ALTER MAPPING cannot be used on existing configurations

C. You must drop the configuration before altering it

D. The dictionary name is misspelled or not created

Solution

1. Step 1: Analyze error message

   The error says the dictionary "english_stem" does not exist, indicating PostgreSQL cannot find that dictionary.

2. Step 2: Identify cause

   Most likely, the dictionary name is misspelled or the dictionary was never created in the database.

3. Final Answer:

   The dictionary name is misspelled or not created -> Option D

4. Quick Check:

   Dictionary must exist before use [OK]

Hint: Check dictionary exists before ALTER MAPPING [OK]

Common Mistakes:

• Assuming ALTER MAPPING is disallowed on configs
• Trying to drop config unnecessarily
• Ignoring dictionary creation step

5. You want to create a search configuration for French that uses the built-in french configuration but replaces the stopword dictionary with a custom dictionary named my_french_stop. Which sequence of commands correctly achieves this?

hard

A. CREATE TEXT SEARCH CONFIGURATION my_french ( COPY = french );
ALTER TEXT SEARCH CONFIGURATION my_french
ALTER MAPPING FOR stopword WITH my_french_stop;

B. CREATE TEXT SEARCH CONFIGURATION my_french ( COPY = french );
ALTER TEXT SEARCH CONFIGURATION my_french
ALTER MAPPING FOR word WITH my_french_stop;

C. CREATE TEXT SEARCH CONFIGURATION my_french AS french;
ALTER TEXT SEARCH CONFIGURATION my_french
ALTER MAPPING FOR stopword WITH my_french_stop;

D. CREATE TEXT SEARCH CONFIGURATION my_french ( COPY = french );
ALTER TEXT SEARCH CONFIGURATION my_french
ALTER MAPPING FOR stopword WITH french;

Solution

1. Step 1: Create configuration by copying french

   Use CREATE TEXT SEARCH CONFIGURATION my_french ( COPY = french ); to clone the built-in french config.

2. Step 2: Alter mapping for stopword dictionary

   Use ALTER MAPPING FOR stopword WITH my_french_stop; to replace the stopword dictionary with the custom one.

3. Final Answer:

   CREATE TEXT SEARCH CONFIGURATION my_french ( COPY = french ); ALTER TEXT SEARCH CONFIGURATION my_french ALTER MAPPING FOR stopword WITH my_french_stop; -> Option A

4. Quick Check:

   Copy config then alter stopword mapping [OK]

Hint: Copy config then ALTER MAPPING for custom dictionaries [OK]

Common Mistakes:

• Using AS instead of COPY = for creation
• Altering wrong token types like word instead of stopword
• Assigning built-in dictionary instead of custom one