SQL WHERE

The WHERE clause is fundamental to SQL queries, allowing you to filter data based on specific conditions.

Key Concepts:

• Basic WHERE syntax
• Comparison operators
• Logical operators
• Pattern matching
• NULL handling

Common Use Cases:

• Finding specific records
• Filtering by date ranges
• Matching patterns
• Excluding data
• Complex conditions

Best Practices:

• Use appropriate operators
• Consider index usage
• Optimize conditions
• Handle NULL values
• Test edge cases

Example Syntax:

SELECT 
    name,
    price,
    category
FROM products
WHERE 
    price >= 100
    AND category = 'Electronics'
    AND stock > 0;

Master basic comparison operators in WHERE clauses.

Business Scenario: Find premium products in your inventory.

Write a query that:

• Lists products
• Filters by price
• Shows key details
• Uses comparison
• Maintains clarity

Requirements:

• Price over $100
• Include name
• Show category
• Clear formatting
• Logical order

Tips:

• Use clear conditions
• Check data types
• Consider ranges
• Format output
• Think about users

Learn to combine multiple conditions using AND and OR operators.

Business Scenario: Find active electronics products.

Write a query that:

• Filters by category
• Checks stock level
• Verifies status
• Combines conditions
• Ensures availability

Key Concepts:

• AND operator
• OR operator
• Operator precedence
• Condition grouping
• Logic flow

Tips:

• Group conditions
• Consider order
• Test combinations
• Use parentheses
• Validate logic

Master pattern matching using LIKE and wildcards.

Business Scenario: Search products by name pattern.

Write a query that:

• Matches patterns
• Uses wildcards
• Shows results
• Handles case
• Improves search

Advanced Concepts:

• LIKE operator
• % wildcard
• _ wildcard
• Case sensitivity
• Pattern efficiency

Tips:

• Use wildcards wisely
• Consider performance
• Test patterns
• Handle special chars
• Think about UX

Learn to filter data within specific ranges.

Business Scenario: Find mid-range products.

Write a query that:

• Checks price range
• Shows products
• Includes details
• Uses BETWEEN
• Maintains clarity

Advanced Techniques:

• BETWEEN operator
• Range boundaries
• Multiple ranges
• Date ranges
• Number ranges

Tips:

• Include boundaries
• Check data types
• Consider indexes
• Test edge cases
• Document ranges

Master the IN operator for multiple value matching.

Business Scenario: Find products in specific categories.

Write a query that:

• Matches categories
• Lists products
• Shows details
• Uses IN clause
• Maintains order

Best Practices:

• List values clearly
• Consider subqueries
• Check performance
• Handle NULL
• Format lists

Tips:

• Group values
• Test membership
• Consider order
• Document choices
• Validate data

Learn to properly handle NULL values in WHERE clauses.

Business Scenario: Find incomplete product records.

Write a query that:

• Checks NULL values
• Shows missing data
• Identifies gaps
• Uses IS NULL
• Improves quality

Advanced Concepts:

• IS NULL
• IS NOT NULL
• NULL comparisons
• Three-valued logic
• Data quality

Tips:

• Never use =NULL
• Check all fields
• Consider meaning
• Plan updates
• Document gaps