BETWEEN range filtering in MySQL - Time & Space Complexity

Time Complexity: BETWEEN range filtering

O(n)

Understanding Time Complexity

When we use BETWEEN to filter data in a database, we want to know how the time to find matching rows changes as the data grows.

We ask: How does the number of rows affect the time it takes to filter with BETWEEN?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

SELECT *
FROM orders
WHERE order_date BETWEEN '2023-01-01' AND '2023-01-31';
    

This query selects all orders placed in January 2023 by checking if the order_date falls within the given date range.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Checking each row's order_date to see if it falls in the date range.
• How many times: Once for every row in the orders table.

How Execution Grows With Input

As the number of rows grows, the database checks more rows to find matches.

Input Size (n)	Approx. Operations
10	10 checks
100	100 checks
1000	1000 checks

Pattern observation: The number of checks grows directly with the number of rows.

Final Time Complexity

Time Complexity: O(n)

This means the time to filter grows in a straight line as the table gets bigger.

Common Mistake

[X] Wrong: "BETWEEN instantly finds the rows without checking many entries."

[OK] Correct: Without an index, the database must look at each row to see if it fits the range, so it takes longer as data grows.

Interview Connect

Understanding how filtering with BETWEEN scales helps you explain query performance clearly and shows you know how databases handle data.

Self-Check

"What if we add an index on order_date? How would the time complexity change?"

Practice

1. What does the BETWEEN operator do in a MySQL query?

easy

A. Filters rows where a column's value is NULL.

B. Filters rows where a column's value is within a specified range, inclusive.

C. Filters rows where a column's value is outside a specified range.

D. Filters rows where a column's value is exactly equal to one value.

Solution

1. Step 1: Understand the purpose of BETWEEN

   The BETWEEN operator is used to filter rows where a column's value falls between two values, including both ends.

2. Step 2: Compare options with definition

   Filters rows where a column's value is within a specified range, inclusive. correctly describes this inclusive range filtering. Other options describe different filters.

3. Final Answer:

   Filters rows where a column's value is within a specified range, inclusive. -> Option B

4. Quick Check:

   BETWEEN means inclusive range filter = D [OK]

Hint: BETWEEN includes both start and end values in range [OK]

Common Mistakes:

• Thinking BETWEEN excludes the end values
• Confusing BETWEEN with equality (=)
• Assuming BETWEEN works only with numbers

2. Which of the following is the correct syntax to select rows where the column age is between 18 and 30?

easy

A. SELECT * FROM users WHERE age BETWEEN 18 & 30;

B. SELECT * FROM users WHERE age BETWEEN (18, 30);

C. SELECT * FROM users WHERE age BETWEEN 18 TO 30;

D. SELECT * FROM users WHERE age BETWEEN 18 AND 30;

Solution

1. Step 1: Recall correct BETWEEN syntax

   The correct syntax uses BETWEEN value1 AND value2 without parentheses or other connectors.

2. Step 2: Check each option

   SELECT * FROM users WHERE age BETWEEN 18 AND 30; uses correct syntax. Options B, C, and D use invalid syntax with commas, TO, or &.

3. Final Answer:

   SELECT * FROM users WHERE age BETWEEN 18 AND 30; -> Option D

4. Quick Check:

   BETWEEN ... AND ... syntax = A [OK]

Hint: BETWEEN syntax always uses AND, no commas or TO [OK]

Common Mistakes:

• Using commas inside BETWEEN
• Replacing AND with TO or &
• Adding parentheses around range values

3. Given the table products with a column price, what will this query return?

SELECT * FROM products WHERE price BETWEEN 50 AND 100;

medium

A. All products with price greater than 50 and less than 100, excluding 50 and 100.

B. All products with price exactly 50 or 100 only.

C. All products with price from 50 up to 100, including both 50 and 100.

D. All products with price less than 50 or greater than 100.

Solution

1. Step 1: Understand BETWEEN inclusiveness

   BETWEEN includes both boundary values, so prices 50 and 100 are included.

2. Step 2: Analyze query result

   The query returns products priced from 50 to 100 inclusive, matching All products with price from 50 up to 100, including both 50 and 100..

3. Final Answer:

   All products with price from 50 up to 100, including both 50 and 100. -> Option C

4. Quick Check:

   BETWEEN includes boundaries = C [OK]

Hint: BETWEEN includes start and end values in results [OK]

Common Mistakes:

• Thinking BETWEEN excludes boundary values
• Confusing BETWEEN with > and < operators
• Assuming BETWEEN works only for numbers

4. Identify the error in this query:

SELECT * FROM orders WHERE order_date BETWEEN '2023-01-01' AND '2023-12-31'

medium

A. No error; the query is correct.

B. BETWEEN cannot be used with date values.

C. The date format is incorrect for BETWEEN.

D. Missing semicolon at the end of the query.

Solution

1. Step 1: Check BETWEEN usage with dates

   BETWEEN works perfectly with date values in MySQL when dates are in 'YYYY-MM-DD' format.

2. Step 2: Verify query syntax

   The query syntax is correct; semicolon is optional in many clients and not an error here.

3. Final Answer:

   No error; the query is correct. -> Option A

4. Quick Check:

   BETWEEN works with dates correctly = A [OK]

Hint: BETWEEN works with numbers, dates, and text [OK]

Common Mistakes:

• Thinking BETWEEN can't filter dates
• Expecting semicolon is mandatory always
• Using wrong date formats like MM-DD-YYYY

5. You want to find all employees hired between January 1, 2020, and December 31, 2022, but your query returns no rows:

SELECT * FROM employees WHERE hire_date BETWEEN '2020-01-01' AND '2022-12-31 23:59:59';

What is the most likely reason and how to fix it?

hard

A. hire_date column stores only dates without time; remove time part from end date.

B. BETWEEN does not work with datetime values; use >= and <= instead.

C. The date format is wrong; use MM-DD-YYYY format.

D. The query is correct; the table is empty.

Solution

1. Step 1: Understand data type of hire_date

   If hire_date stores only DATE (no time), comparing with '2022-12-31 23:59:59' fails because time part is ignored or mismatched.

2. Step 2: Fix the query

   Use '2022-12-31' without time to match date-only values correctly.

3. Final Answer:

   hire_date column stores only dates without time; remove time part from end date. -> Option A

4. Quick Check:

   Match data type format in BETWEEN range = B [OK]

Hint: Match data types exactly when using BETWEEN with dates [OK]

Common Mistakes:

• Adding time to date-only columns in BETWEEN
• Assuming BETWEEN fails with datetime
• Using wrong date formats