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Common situations of mysql index failure
PHP Chinese website brings to you common situations in which mysql indexes fail: 1. Using functions or operations; 2. Implicit type conversion; 3. Using not equal to (!= or <>); 4. Using the LIKE operator, and Starting with a wildcard; 5. OR condition; 6. NULL value; 7. Low index selectivity, etc.
Several situations of mysql index failureCommon situations: 1. Use functions or operations; 2. Implicit type conversion; 3. Use not equal to (!= or <>); 4. Use the LIKE operator and start with a wildcard; 5. OR conditions; 6. NULL Value; 7. Low index selectivity; 8. Leftmost prefix principle of composite index; 9. Optimizer decision; 10. FORCE INDEX and IGNORE INDEX.
Situation causing MySQL index failureSeveral situations of MySQL index failure and code examples Introduction: In the MySQL database, indexes are one of the important factors to improve query performance. However, sometimes we find that the index does not play the expected role, query performance is not improved, and even causes the query to become slower. The reason is probably that the index is invalid. This article will introduce several common situations that cause MySQL index failure and give corresponding code examples. 1. Use functions or expressions to perform operations on index columns. If the index columns are used in the query statement,
How to solve MySQL index failure1. Preface When performing an index query on a SQL statement, you will encounter an index failure, which has a crucial impact on the feasibility and performance efficiency of the statement. This article analyzes why the index fails and what situations will cause the index to fail. As well as optimization solutions for index failure, it focuses on the leftmost prefix matching principle, MySQL logical architecture and optimizer, index failure scenarios and why it fails. 2. The leftmost prefix matching principle. I have previously written an article about the characteristics and optimization issues of adding indexes to MySQL. The following will introduce the relevant content of index failure. First, introduce a principle that will be used in the subsequent causes of index failure: the leftmost prefix matching principle. The underlying principle of the leftmost prefix: when establishing a joint index in MySQL
What are the situations in which mysql index fails?Index failure: 1. The like query starts with "%"; 2. The index is not used before and after the or statement; 3. The first column index is not used in the combined index; 4. "IS NULL" or "IS NULL" is used on the index column. IS NOT NULL" operation; 5. Use "not", "<>", "!=", etc. on the index field.
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