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Make use of Indexing: Ensure that the columns used in the WHERE clause are indexed. Indexing enables the database engine to quickly locate the required rows, reducing the time taken to fetch the results. Use the EXPLAIN statement or database profiling tools to verify index usage.
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Avoid Functions or Expressions: Applying functions or expressions on columns in the WHERE clause can prevent the use of indexes, resulting in slower query execution. If possible, modify the query structure to avoid wrapping columns with functions or expressions.
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Use Appropriate Comparison Operators: Choose the most appropriate comparison operator for the specific condition. For example, use “=” for exact matches, “<>” for non-matches, and “<” or “>” for range queries. Using the correct operator improves the chances of index utilization and query performance.
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Be Mindful of NULL Values: NULL values can impact query results and performance. Ensure that your WHERE clause handles NULL values correctly, using the IS NULL or IS NOT NULL operators. Be cautious when using equality operators with NULL values, as they may produce unexpected results.
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Avoid Wildcard Matching at the Start of LIKE Clauses: When using the LIKE operator, avoid starting the pattern with a wildcard character (“%”). Starting the pattern with a wildcard prevents index usage and forces a table scan. Instead, consider using a full-text search solution or place the wildcard at the end of the pattern for more efficient searching.
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Combine Conditions Using Logical Operators: Use logical operators (AND, OR) to combine multiple conditions in the WHERE clause efficiently. Group related conditions together using parentheses to ensure the correct order of evaluation. Using logical operators effectively helps narrow down the search space.
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Regularly Update Statistics: Keep table statistics up-to-date to enable the query optimizer to make informed decisions. Outdated statistics can lead to suboptimal execution plans and hinder query performance.
Remember that optimization techniques may vary across different database management systems. So familiarize yourself with the specific syntax and features of your chosen platform.
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