Password policies in MySQL - Time & Space Complexity

Time Complexity: Password policies

O(n)

Understanding Time Complexity

When checking password policies in a database, we want to know how the time to verify passwords changes as more passwords or rules are involved.

We ask: How does the work grow when we check many passwords or apply multiple rules?

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

-- Check if a password meets policy rules
SELECT password
FROM users
WHERE LENGTH(password) >= 8
  AND password REGEXP '[A-Z]'
  AND password REGEXP '[a-z]'
  AND password REGEXP '[0-9]'
  AND password NOT REGEXP '[ ]';
    

This code checks each user's password against several rules: minimum length, contains uppercase, lowercase, digit, and no spaces.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: Checking each password against multiple pattern rules.
• How many times: Once per password in the users table.

How Execution Grows With Input

As the number of users grows, the database checks more passwords one by one.

Input Size (n)	Approx. Operations
10	Checks 10 passwords against all rules
100	Checks 100 passwords against all rules
1000	Checks 1000 passwords against all rules

Pattern observation: The work grows directly with the number of passwords; doubling passwords doubles the checks.

Final Time Complexity

Time Complexity: O(n)

This means the time to check passwords grows in a straight line with the number of passwords.

Common Mistake

[X] Wrong: "Checking multiple rules makes the time grow much faster than the number of passwords."

[OK] Correct: Each password is checked against all rules in a fixed number of steps, so the total time grows mainly with how many passwords there are, not the number of rules.

Interview Connect

Understanding how password checks scale helps you design systems that stay fast even as users grow. This skill shows you can think about real-world database performance.

Self-Check

"What if we added a loop to check each password against a list of 10 different forbidden words? How would the time complexity change?"

Practice

1. What is the purpose of MySQL's validate_password_policy variable?

easy

A. To set rules for creating strong passwords

B. To control user access privileges

C. To define database storage engines

D. To manage query cache size

Solution

1. Step 1: Understand the variable name

   The variable validate_password_policy relates to password validation rules.

2. Step 2: Identify its function

   It sets rules to ensure passwords are strong and secure.

3. Final Answer:

   To set rules for creating strong passwords -> Option A

4. Quick Check:

   Password policy = Set rules for strong passwords [OK]

Hint: Policy variables control password strength rules [OK]

Common Mistakes:

• Confusing password policy with user privileges
• Thinking it manages database storage
• Assuming it controls query cache

2. Which of the following is the correct syntax to check the current password policy level in MySQL?

easy

A. SHOW PASSWORD POLICY;

B. SELECT * FROM validate_password_policy;

C. SHOW VARIABLES LIKE 'validate_password_policy';

D. GET VARIABLES 'validate_password_policy';

Solution

1. Step 1: Recall how to view system variables

   MySQL uses SHOW VARIABLES LIKE 'variable_name'; to display variable values.

2. Step 2: Match the variable name

   The variable for password policy is validate_password_policy, so the correct syntax is SHOW VARIABLES LIKE 'validate_password_policy';

3. Final Answer:

   SHOW VARIABLES LIKE 'validate_password_policy'; -> Option C

4. Quick Check:

   SHOW VARIABLES LIKE 'validate_password_policy' [OK]

Hint: Use SHOW VARIABLES LIKE for system settings [OK]

Common Mistakes:

• Using SELECT on a variable name
• Trying non-existent commands like SHOW PASSWORD POLICY
• Using GET VARIABLES which is invalid syntax

3. Given the following commands executed in MySQL:

SET GLOBAL validate_password_length = 10;
SHOW VARIABLES LIKE 'validate_password_length';

What will be the output of the SHOW VARIABLES command?

medium

A. Variable_name: validate_password_length, Value: 10

B. Variable_name: validate_password_length, Value: 8

C. Syntax error

D. Variable_name: validate_password_policy, Value: 10

Solution

1. Step 1: Understand the SET GLOBAL command

   The command sets the global password length requirement to 10 characters.

2. Step 2: SHOW VARIABLES output

   The SHOW VARIABLES LIKE 'validate_password_length'; will display the current value, which is now 10.

3. Final Answer:

   Variable_name: validate_password_length, Value: 10 -> Option A

4. Quick Check:

   SET GLOBAL changes variable, SHOW displays updated value [OK]

Hint: SET GLOBAL changes variable, SHOW displays current value [OK]

Common Mistakes:

• Expecting default value instead of updated
• Confusing variable names
• Assuming syntax error from SET GLOBAL

4. You tried to set the password policy level with this command:

SET GLOBAL validate_password_policy = 'STRONG';

But MySQL returned an error. What is the likely cause?

medium

A. The command requires quotes around the variable name

B. The variable name is incorrect

C. You must use SET SESSION instead of SET GLOBAL

D. The value should be an integer, not a string

Solution

1. Step 1: Check variable type for validate_password_policy

   This variable expects an integer value (0,1,2) representing policy levels, not strings.

2. Step 2: Understand error cause

   Using a string like 'STRONG' causes a type mismatch error.

3. Final Answer:

   The value should be an integer, not a string -> Option D

4. Quick Check:

   Policy level = integer, not string [OK]

Hint: Policy levels use numbers, not words [OK]

Common Mistakes:

• Using string values instead of integers
• Mistyping variable name
• Confusing SET GLOBAL with SET SESSION

5. You want to enforce a password policy that requires passwords to be at least 12 characters long, include mixed case letters, numbers, and special characters. Which combination of MySQL variables should you set to achieve this?

hard

A. SET GLOBAL validate_password_length = 10; SET GLOBAL validate_password_policy = 0;

B. SET GLOBAL validate_password_length = 12; SET GLOBAL validate_password_policy = 2;

C. SET GLOBAL validate_password_length = 12; SET GLOBAL validate_password_policy = 1;

D. SET GLOBAL validate_password_length = 8; SET GLOBAL validate_password_policy = 0;

Solution

1. Step 1: Understand password length requirement

   You want at least 12 characters, so validate_password_length must be set to 12.

2. Step 2: Understand policy levels

   Policy level 2 (STRONG) requires mixed case, numbers, and special characters.

3. Step 3: Match variables to requirements

   Setting validate_password_policy = 2 and length to 12 enforces all requirements.

4. Final Answer:

   SET GLOBAL validate_password_length = 12; SET GLOBAL validate_password_policy = 2; -> Option B

5. Quick Check:

   Length 12 + policy 2 = strong password rules [OK]

Hint: Policy 2 = strong; length sets minimum characters [OK]

Common Mistakes:

• Using policy 0 or 1 which are weaker
• Setting length less than required
• Confusing policy levels with string values