GIN index for arrays and JSONB in PostgreSQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a GIN index on a JSONB column named 'data'.

PostgreSQL

CREATE INDEX idx_data_gin ON my_table USING [1] (data);

Drag options to blanks, or click blank then click option'

Agist

Bhash

Cbtree

Dgin

Attempts:

3 left

💡 Hint

Common Mistakes

Using btree index type which does not support JSONB efficiently.

Using hash index which is not suitable for JSONB.

Using gist index which is less efficient for JSONB arrays.

The GIN index type is used for indexing JSONB columns efficiently in PostgreSQL.

2fill in blank

medium

Complete the code to create a GIN index on an array column named 'tags'.

PostgreSQL

CREATE INDEX idx_tags_gin ON articles USING gin([1]);

Drag options to blanks, or click blank then click option'

AARRAY[tags]

Btags[]

Ctags

Dtags::text

Attempts:

3 left

💡 Hint

Common Mistakes

Adding brackets or casting the column which causes syntax errors.

Using ARRAY[] syntax which is invalid in this context.

The column name 'tags' is used directly inside the index definition for GIN indexing of arrays.

3fill in blank

hard

Fix the error in the code to create a GIN index on a JSONB column 'info'.

PostgreSQL

CREATE INDEX idx_info_gin ON users USING gin (info [1]);

Drag options to blanks, or click blank then click option'

Ajsonb_ops

Bjsonb_path_ops

Cjson_ops

Djsonb_index_ops

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'json_ops' which is invalid for JSONB.

Using 'jsonb_index_ops' which does not exist.

The 'jsonb_ops' operator class is the default and supports all JSONB queries.

4fill in blank

hard

Fill both blanks to create a GIN index on a JSONB column 'attributes' with a specific operator class.

PostgreSQL

CREATE INDEX idx_attributes_gin ON products USING [1] (attributes [2]);

Drag options to blanks, or click blank then click option'

Agin

Bbtree

Cjsonb_path_ops

Dgist

Attempts:

3 left

💡 Hint

Common Mistakes

Using btree or gist index types which are not suitable.

Omitting the operator class or using an invalid one.

Use 'gin' as the index type and 'jsonb_path_ops' as the operator class for efficient JSONB indexing.

5fill in blank

hard

Fill all three blanks to create a GIN index on an array column 'keywords' with a custom operator class.

PostgreSQL

CREATE INDEX idx_keywords_gin ON documents USING [1] ([2] [3]);

Drag options to blanks, or click blank then click option'

Agin

Bkeywords

Carray_ops

Dbtree

Attempts:

3 left

💡 Hint

Common Mistakes

Using btree index type which is invalid for arrays.

Using wrong operator class or omitting it.

Use 'gin' as the index type, the column name 'keywords', and the operator class 'array_ops' for integer arrays.

Practice

1. What is the main purpose of a GIN index in PostgreSQL when used with arrays or JSONB columns?

easy

A. To speed up searches for specific elements inside arrays or JSONB data

B. To compress the data stored in arrays or JSONB columns

C. To automatically update array or JSONB data when rows change

D. To enforce uniqueness on array or JSONB columns

Solution

1. Step 1: Understand GIN index purpose

   GIN indexes are designed to speed up searches inside complex data types like arrays and JSONB by indexing their elements.

2. Step 2: Compare options

   Options B, C, and D describe compression, automatic updates, and uniqueness enforcement, which are not the main roles of GIN indexes.

3. Final Answer:

   To speed up searches for specific elements inside arrays or JSONB data -> Option A

4. Quick Check:

   GIN index purpose = speed up element search [OK]

Hint: GIN indexes speed up element searches inside arrays/JSONB [OK]

Common Mistakes:

• Confusing GIN with data compression
• Thinking GIN enforces uniqueness
• Assuming GIN auto-updates data

2. Which of the following is the correct syntax to create a GIN index on a JSONB column named data in a table items?

easy

A. CREATE INDEX idx_data ON items USING HASH (data);

B. CREATE INDEX idx_data ON items USING GIN (data);

C. CREATE INDEX idx_data ON items USING GIN (data jsonb_path_ops);

D. CREATE INDEX idx_data ON items USING BTREE (data);

Solution

1. Step 1: Identify correct index type for JSONB

   GIN indexes are created using USING GIN and applied directly on the JSONB column.

2. Step 2: Check syntax correctness

   CREATE INDEX idx_data ON items USING GIN (data); uses correct syntax: CREATE INDEX idx_data ON items USING GIN (data); CREATE INDEX idx_data ON items USING GIN (data jsonb_path_ops); is invalid because jsonb_path_ops must be specified inside parentheses, e.g., data jsonb_path_ops is incorrect syntax here.

3. Final Answer:

   CREATE INDEX idx_data ON items USING GIN (data); -> Option B

4. Quick Check:

   Correct GIN index syntax = CREATE INDEX idx_data ON items USING GIN (data); [OK]

Hint: Use 'USING GIN (column)' to create GIN index on JSONB [OK]

Common Mistakes:

• Using BTREE or HASH instead of GIN
• Incorrect syntax with jsonb_path_ops
• Missing USING keyword

3. Given the table products with a JSONB column tags and a GIN index on tags, what will the following query return?

SELECT id FROM products WHERE tags @> '["organic"]';

medium

A. All product ids where the tags array contains the element 'organic'

B. All product ids where the tags array is exactly '["organic"]'

C. All product ids where the tags array contains any element

D. Syntax error due to incorrect JSONB operator

Solution

1. Step 1: Understand the JSONB containment operator @>

   The operator @> checks if the left JSONB contains the right JSONB. Here, it checks if tags contains the element 'organic'.

2. Step 2: Analyze the query result

   The query returns all product ids where the tags array includes 'organic' anywhere, not just exact match or any element.

3. Final Answer:

   All product ids where the tags array contains the element 'organic' -> Option A

4. Quick Check:

   tags @> '["organic"]' means contains 'organic' [OK]

Hint: Use @> to check if JSONB contains specific element [OK]

Common Mistakes:

• Thinking @> means exact match
• Confusing @> with existence of any element
• Assuming syntax error with @>

4. You created a GIN index on a JSONB column info but your queries using info @> '{"key": "value"}' are still slow. What is the most likely cause?

medium

A. GIN indexes do not support the @> operator

B. The queries are missing the WHERE clause

C. The GIN index was created without the jsonb_path_ops operator class

D. The JSONB column contains NULL values

Solution

1. Step 1: Understand GIN index operator classes

   GIN indexes on JSONB can use default or jsonb_path_ops operator class. The latter is optimized for existence queries using @>.

2. Step 2: Identify cause of slow queries

   If the index was created without jsonb_path_ops, the index may not efficiently support @> queries, causing slow performance.

3. Final Answer:

   The GIN index was created without the jsonb_path_ops operator class -> Option C

4. Quick Check:

   Missing jsonb_path_ops = slow @> queries [OK]

Hint: Use jsonb_path_ops for faster @> queries on JSONB [OK]

Common Mistakes:

• Assuming GIN doesn't support @>
• Ignoring operator class choice
• Blaming NULL values for index slowness

5. You want to create a GIN index on a table orders with a column items that stores an array of integers. Which statement correctly creates the index and optimizes queries checking if an integer is present in the array?

hard

A. CREATE INDEX idx_items_gin ON orders USING GIN (items gin_int_ops);

B. CREATE INDEX idx_items_gin ON orders USING GIN (items gin__int_ops);

C. CREATE INDEX idx_items_gin ON orders USING GIN (items gin__intarray_ops);

D. CREATE INDEX idx_items_gin ON orders USING GIN (items);

Solution

1. Step 1: Identify correct GIN index syntax for integer arrays

   For integer arrays, the default GIN index supports containment and membership queries without specifying operator classes.

2. Step 2: Validate options

   Options B, C, and D use invalid operator class names like gin__int_ops or gin__intarray_ops, which do not exist in PostgreSQL.

3. Final Answer:

   CREATE INDEX idx_items_gin ON orders USING GIN (items); -> Option D

4. Quick Check:

   Default GIN index on array column = CREATE INDEX idx_items_gin ON orders USING GIN (items); [OK]

Hint: Use default GIN index on array column without extra ops [OK]

Common Mistakes:

• Using non-existent operator classes
• Adding unnecessary syntax after column name
• Confusing GIN with other index types