EXPLAIN plan for query analysis in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to show the execution plan of a query.

SQL

EXPLAIN [1] SELECT * FROM employees;

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

AANALYZE

BPLAN

CQUERY

DEXECUTE

Attempts:

3 left

💡 Hint

Common Mistakes

Using EXPLAIN PLAN instead of EXPLAIN ANALYZE.

Using EXPLAIN QUERY which is not valid.

Using EXPLAIN EXECUTE which is incorrect.

The EXPLAIN ANALYZE command runs the query and shows the actual execution plan with timing details.

2fill in blank

medium

Complete the code to get a summary of the query plan without running the query.

SQL

EXPLAIN [1] FOR SELECT * FROM orders WHERE order_date > '2023-01-01';

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

AANALYZE

BPLAN

CSELECT

DVERBOSE

Attempts:

3 left

💡 Hint

Common Mistakes

Using EXPLAIN ANALYZE which runs the query.

Using EXPLAIN VERBOSE which is not standard.

Using EXPLAIN SELECT which is invalid.

EXPLAIN PLAN shows the estimated execution plan without running the query.

3fill in blank

hard

Fix the error in the EXPLAIN command to correctly show the query plan.

SQL

EXPLAIN [1] SELECT name FROM customers WHERE city = 'Paris';

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

AANALYZE

BEXECUTE

CPLAN

DRUN

Attempts:

3 left

💡 Hint

Common Mistakes

Using EXPLAIN PLAN which does not run the query.

Using EXPLAIN EXECUTE which is invalid.

Using EXPLAIN RUN which is not a valid keyword.

The correct keyword to run the query and show the actual plan is ANALYZE.

4fill in blank

hard

Fill both blanks to create a query that explains the plan and shows detailed output.

SQL

EXPLAIN [1] [2] SELECT * FROM products WHERE price > 100;

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

AANALYZE

BVERBOSE

CPLAN

DEXECUTE

Attempts:

3 left

💡 Hint

Common Mistakes

Using PLAN instead of ANALYZE to run the query.

Using EXECUTE which is invalid.

Swapping the order of ANALYZE and VERBOSE.

Using EXPLAIN ANALYZE VERBOSE runs the query and shows a detailed execution plan.

5fill in blank

hard

Fill all three blanks to explain the query plan with analyze, verbose, and buffers options.

SQL

EXPLAIN [1] [2] [3] SELECT * FROM sales WHERE amount > 500;

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

AANALYZE

BVERBOSE

CBUFFERS

DPLAN

Attempts:

3 left

💡 Hint

Common Mistakes

Using PLAN instead of ANALYZE to run the query.

Missing BUFFERS option for buffer info.

Wrong order of options.

EXPLAIN ANALYZE VERBOSE BUFFERS runs the query and shows detailed plan with buffer usage.

Practice

1. What is the main purpose of using EXPLAIN before running a SQL query?

easy

A. To see how the database plans to execute the query

B. To delete data from the database

C. To create a new table

D. To insert new rows into a table

Solution

1. Step 1: Understand the role of EXPLAIN

   EXPLAIN shows the steps the database will take to run a query, like a map of the plan.

2. Step 2: Identify the correct purpose

   It helps find slow parts and optimize queries, not to modify data or structure.

3. Final Answer:

   To see how the database plans to execute the query -> Option A

4. Quick Check:

   EXPLAIN = query plan [OK]

Hint: EXPLAIN shows query steps, not data changes [OK]

Common Mistakes:

• Thinking EXPLAIN modifies data
• Confusing EXPLAIN with data manipulation commands
• Assuming EXPLAIN creates or deletes tables

2. Which of the following is the correct syntax to get the execution plan of a query in SQL?

easy

A. EXPLAIN SELECT * FROM users;

B. PLAN EXPLAIN SELECT * FROM users;

C. SHOW PLAN FOR SELECT * FROM users;

D. RUN EXPLAIN ON SELECT * FROM users;

Solution

1. Step 1: Recall standard EXPLAIN syntax

   The standard way to get a query plan is to put EXPLAIN before the query.

2. Step 2: Check each option

   Only EXPLAIN SELECT * FROM users; uses the correct syntax: EXPLAIN SELECT ...; others are invalid or non-standard.

3. Final Answer:

   EXPLAIN SELECT * FROM users; -> Option A

4. Quick Check:

   EXPLAIN + query = correct syntax [OK]

Hint: Put EXPLAIN before the query to see the plan [OK]

Common Mistakes:

• Adding extra keywords like PLAN or RUN
• Using SHOW PLAN which is not standard SQL
• Placing EXPLAIN after the query

3. Given the query SELECT * FROM orders WHERE customer_id = 5;, what does the EXPLAIN plan typically show?

medium

A. The syntax errors in the query

B. The total number of rows in the orders table

C. The list of all customers in the database

D. The steps to scan the orders table and filter rows where customer_id = 5

Solution

1. Step 1: Understand what EXPLAIN outputs

   EXPLAIN shows how the database will find rows, like scanning and filtering steps.

2. Step 2: Match the query with the plan description

   The query filters orders by customer_id = 5, so the plan shows scanning and filtering those rows.

3. Final Answer:

   The steps to scan the orders table and filter rows where customer_id = 5 -> Option D

4. Quick Check:

   EXPLAIN = scan + filter steps [OK]

Hint: EXPLAIN shows how rows are found and filtered [OK]

Common Mistakes:

• Thinking EXPLAIN shows data counts
• Expecting EXPLAIN to list unrelated tables
• Confusing EXPLAIN output with errors

4. You run EXPLAIN SELECT name FROM employees WHERE age > 30; but get an error. What is the most likely cause?

medium

A. The EXPLAIN keyword is not supported in your SQL dialect

B. The query is missing a semicolon at the end

C. The table employees does not exist

D. The WHERE clause uses an invalid operator

Solution

1. Step 1: Check common EXPLAIN errors

   EXPLAIN syntax is usually supported; missing semicolon rarely causes errors in many tools.

2. Step 2: Consider table existence

   If the table does not exist, EXPLAIN cannot analyze the query and will error.

3. Final Answer:

   The table employees does not exist -> Option C

4. Quick Check:

   Missing table = EXPLAIN error [OK]

Hint: Check if tables exist before EXPLAIN [OK]

Common Mistakes:

• Assuming EXPLAIN is unsupported
• Blaming missing semicolon
• Thinking WHERE operator is invalid

5. You want to optimize a slow query joining two large tables. How can using EXPLAIN help you improve performance?

hard

A. By deleting duplicate rows from the tables

B. By showing which table is scanned first and if indexes are used

C. By automatically rewriting the query for better speed

D. By increasing the database server memory

Solution

1. Step 1: Understand EXPLAIN's role in optimization

   EXPLAIN shows the order of table scans and whether indexes help speed up lookups.

2. Step 2: Identify how this helps optimization

   Knowing scan order and index use helps rewrite queries or add indexes to improve speed.

3. Final Answer:

   By showing which table is scanned first and if indexes are used -> Option B

4. Quick Check:

   EXPLAIN reveals scan order and index use [OK]

Hint: EXPLAIN reveals scan order and index usage [OK]

Common Mistakes:

• Expecting EXPLAIN to fix queries automatically
• Confusing EXPLAIN with data cleanup
• Thinking EXPLAIN changes server settings