Full-text indexes in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a full-text index in MySQL?

A full-text index is a special type of index in MySQL that allows fast searching of text columns for words or phrases, enabling efficient text-based searches.

beginner

Which MySQL storage engines support full-text indexes?

MyISAM and InnoDB storage engines support full-text indexes in MySQL.

beginner

How do you create a full-text index on a column named 'content' in a table 'articles'?

You use the SQL command:
CREATE FULLTEXT INDEX idx_content ON articles(content);

beginner

What SQL clause is used to perform a full-text search in MySQL?

The MATCH() AGAINST() clause is used to perform full-text searches in MySQL.

intermediate

What is the difference between natural language mode and boolean mode in full-text searches?

Natural language mode searches for relevant words without operators, ranking results by relevance. Boolean mode allows use of operators like +, -, * to refine search conditions.

Which MySQL command creates a full-text index on the 'description' column of the 'products' table?

A CREATE FULLTEXT INDEX idx_desc ON products(description);

B CREATE INDEX idx_desc ON products(description);

C CREATE TEXT INDEX idx_desc ON products(description);

D CREATE FULLTEXT KEY idx_desc ON products(description);

The correct syntax to create a full-text index is CREATE FULLTEXT INDEX followed by the index name and the table and column.

Which storage engine in MySQL supports full-text indexes by default?

A MEMORY

B InnoDB

C CSV

D ARCHIVE

InnoDB supports full-text indexes starting from MySQL 5.6 and later.

What does the MATCH() function do in a full-text search?

A Filters rows by exact match

B Defines the index to use

C Creates a new full-text index

D Specifies the columns to search in

MATCH() specifies which columns to search for the given text in a full-text search.

Which mode allows use of operators like + and - in full-text searches?

A Boolean mode

B Natural language mode

C Query expansion mode

D Exact match mode

Boolean mode allows operators to refine search queries.

What is a limitation of full-text indexes in MySQL?

A They only work on numeric columns

B They cannot be used on InnoDB tables

C They require text-based columns like CHAR, VARCHAR, or TEXT

D They automatically index all columns

Full-text indexes work only on text-based columns such as CHAR, VARCHAR, or TEXT.

Explain how to create and use a full-text index in MySQL for searching text data.

Think about the steps from creating the index to querying with it.

Describe the benefits and limitations of using full-text indexes in MySQL.

Consider both what full-text indexes help with and what to watch out for.

Practice

1. What is the main purpose of a FULLTEXT index in MySQL?

easy

A. To speed up searching for words inside text columns

B. To enforce uniqueness on text columns

C. To sort text columns alphabetically

D. To compress text data for storage

Solution

1. Step 1: Understand what FULLTEXT indexes do

   FULLTEXT indexes are designed to make searching for words inside large text columns faster and more efficient.

2. Step 2: Compare with other index types

   Unlike unique or sorting indexes, FULLTEXT indexes focus on text search, not uniqueness or ordering.

3. Final Answer:

   To speed up searching for words inside text columns -> Option A

4. Quick Check:

   FULLTEXT index = speeds up text search [OK]

Hint: FULLTEXT indexes are for fast word searches in text columns [OK]

Common Mistakes:

• Confusing FULLTEXT with UNIQUE index
• Thinking FULLTEXT sorts data
• Assuming FULLTEXT compresses data

2. Which of the following is the correct syntax to create a FULLTEXT index on the column description in a table products?

easy

A. CREATE INDEX idx_desc FULLTEXT ON products(description);

B. CREATE INDEX idx_desc ON products(description) FULLTEXT;

C. CREATE FULLTEXT INDEX idx_desc ON products(description);

D. CREATE FULLTEXT ON products(description) INDEX idx_desc;

Solution

1. Step 1: Recall correct FULLTEXT index syntax

   The correct syntax is: CREATE FULLTEXT INDEX index_name ON table_name(column_name);

2. Step 2: Match syntax with options

   CREATE FULLTEXT INDEX idx_desc ON products(description); matches the correct syntax exactly.

3. Final Answer:

   CREATE FULLTEXT INDEX idx_desc ON products(description); -> Option C

4. Quick Check:

   CREATE FULLTEXT INDEX ... ON ... [OK]

Hint: FULLTEXT index syntax: CREATE FULLTEXT INDEX name ON table(column) [OK]

Common Mistakes:

• Placing FULLTEXT keyword after INDEX
• Using wrong order of keywords
• Omitting INDEX keyword

3. Given a table articles with a FULLTEXT index on the content column, what will the following query return?

SELECT id FROM articles WHERE MATCH(content) AGAINST('database');

medium

A. Syntax error because MATCH() requires multiple columns

B. All article IDs sorted alphabetically by content

C. All article IDs where content exactly equals 'database'

D. All article IDs where the word 'database' appears in content

Solution

1. Step 1: Understand MATCH() AGAINST() usage

   This function searches the FULLTEXT indexed column for the given word or phrase.

2. Step 2: Interpret the query result

   The query returns IDs of rows where 'database' appears anywhere in the content column.

3. Final Answer:

   All article IDs where the word 'database' appears in content -> Option D

4. Quick Check:

   MATCH() AGAINST() = full-text search result [OK]

Hint: MATCH() AGAINST() finds rows containing the search word [OK]

Common Mistakes:

• Thinking it matches exact whole content
• Assuming it sorts results
• Believing MATCH() needs multiple columns

4. You wrote this query but it returns no results even though matching rows exist:

SELECT * FROM posts WHERE MATCH(body) AGAINST('the');

The body column has a FULLTEXT index. What is the likely problem?

medium

A. AGAINST() requires the IN BOOLEAN MODE modifier

B. The word 'the' is too common and ignored by default stopword list

C. FULLTEXT index must be created on multiple columns

D. MATCH() cannot be used on a single column

Solution

1. Step 1: Recall FULLTEXT stopword behavior

   MySQL ignores very common words (stopwords) by default in FULLTEXT searches.

2. Step 2: Understand why no results appear

   If 'the' is in the stopword list, the search ignores it, returning no matches.

3. Final Answer:

   The word 'the' is too common and ignored by default stopword list -> Option B

4. Quick Check:

   Stopwords cause no results for common words [OK]

Hint: Common words may be ignored by FULLTEXT stopword list [OK]

Common Mistakes:

• Thinking MATCH() needs multiple columns
• Assuming IN BOOLEAN MODE is always required
• Believing FULLTEXT index must cover multiple columns

5. You want to find rows in the reviews table where the comment column contains either 'fast' or 'reliable'. The comment column has a FULLTEXT index. Which query correctly finds these rows using boolean mode?

hard

A. SELECT * FROM reviews WHERE MATCH(comment) AGAINST('fast | reliable' IN BOOLEAN MODE);

B. SELECT * FROM reviews WHERE MATCH(comment) AGAINST('+fast +reliable' IN BOOLEAN MODE);

C. SELECT * FROM reviews WHERE MATCH(comment) AGAINST('fast reliable' IN BOOLEAN MODE);

D. SELECT * FROM reviews WHERE MATCH(comment) AGAINST('"fast reliable"' IN BOOLEAN MODE);

Solution

1. Step 1: Understand boolean mode operators

   In boolean mode, | means OR, + means AND, and quotes mean phrase search.

2. Step 2: Identify correct OR query

   To find rows containing either 'fast' OR 'reliable', use 'fast | reliable'.

3. Step 3: Check other options

   SELECT * FROM reviews WHERE MATCH(comment) AGAINST('fast reliable' IN BOOLEAN MODE); searches for both words but not as OR; SELECT * FROM reviews WHERE MATCH(comment) AGAINST('+fast +reliable' IN BOOLEAN MODE); requires both words; SELECT * FROM reviews WHERE MATCH(comment) AGAINST('"fast reliable"' IN BOOLEAN MODE); searches exact phrase.

4. Final Answer:

   SELECT * FROM reviews WHERE MATCH(comment) AGAINST('fast | reliable' IN BOOLEAN MODE); -> Option A

5. Quick Check:

   Boolean OR uses | operator [OK]

Hint: Use | for OR in boolean full-text searches [OK]

Common Mistakes:

• Using space for OR instead of |
• Using + which means AND
• Using quotes for phrase instead of OR