Article Introduction：MySQL is a widely used relational database management system. During development, indexes can improve query efficiency, but sometimes you encounter index failure, which causes queries to slow down or even make it impossible to use the index. This article will introduce the causes of index failure, how to detect index failure, how to optimize the index, and some practical cases. 1. Reasons for index failure 1. Functions are used on index columns. For example: SELECT * FROM user WHERE DATE_FORMAT(create_time,'%Y-%m-%d

2023-05-14 comment 0  2377

Article Introduction：MySQL is a popular relational database management system, and indexes are one of the important tools for performance optimization in MySQL. Although indexes can improve query performance, the performance of a MySQL database will be severely affected when indexes become invalid. This article will explore the causes of index failure in MySQL and how to avoid this situation. 1. Reasons for index failure 1. Data duplication When data in a table is duplicated, MySQL's query planner may decide to give up using the index because it believes that a full table scan is faster and more effective. This is because in the index

2023-05-14 comment 0  2083

Article Introduction：1. 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

2023-06-04 comment 0  2881

Article Introduction：This article will record a Mysql index failure and analyze the reasons for Mysql index failure. I hope it will be helpful to you!

2021-11-02 comment 0  4837

Article Introduction：In Oracle, you can use the "select status from user_indexes where index_name='index name';" statement to determine whether the index is invalid; if the returned result is VALID, it means that the index is not invalid, otherwise it means that the index is invalid.

2022-05-25 comment 0  6185

Article Introduction：Several 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,

2024-02-18 comment 0  1030

Article Introduction：MySQL is a commonly used relational database management system, and indexes are crucial for optimizing the performance of database queries. However, sometimes it is found that even if an index is built, the query is still very slow. At this time, it is necessary to consider the cause of index failure and perform corresponding optimization. Among them, in query may be one of the common causes of index failure. 1. In query In query is a commonly used query method in MySQL, which can match multiple values ​​or multiple ranges in one query. For example: ```SELECT * FROM table WHE

2023-05-14 comment 0  4968

Article Introduction：Method: 1. Use the "select status from user_indexes where index_name='index name'" statement. If the result returns VALID, the index is not invalid; 2. Use the "select status from DBA_IND_PARTITIONS" statement to view the partition index status; 3. Use "select status from dba_indexes" to view the normal index status.

2022-06-10 comment 0  16018

Article Introduction：The situations where the index fails include: 1. When calculating a column or using a function; 2. When using reverse operation or link operation; 3. When using or in the where statement, if one column does not have an index, then the other columns will be indexed. will fail.

2019-04-29 comment 0  37580

Article Introduction：Several cases of mysql index failure: 1. There is or in the condition, even if there is a condition with an index, it will not be used; 2. For a multi-column index, if the first part is not used, the index will not be used; 3. Like query starts with %, the index is invalid; 4. When the field type is a string, the data in the condition is not quoted in quotation marks.

2020-10-09 comment 0  18038

Article Introduction：The IN statement in MySQL is a very common query statement that can query multiple values ​​at one time, for example: SELECT * FROM table WHERE id IN (1,2,3,4); this query statement will return the id of 1, Rows 2, 3, and 4. The benefit of the IN statement is that it allows us to query multiple values ​​at once without having to use multiple OR statements. However, when there are many values ​​in the IN statement, it may cause index failure, which will seriously affect query efficiency. Let’s take a look at why index failure occurs

2023-05-18 comment 0  1039

Article Introduction：Conclusion The following specific cases describe in detail the scenarios that are not suitable for indexing: it is not recommended to create indexes for tables with relatively small data volumes. It is not recommended to create indexes for fields with a large amount of repeated data (similar to: gender fields). It is not recommended to create indexes for tables that require frequent updates. The unused fields behind the index where, groupby, and orderby are not indexed. Do not define redundant indexes. Scenarios for index failure: Use the filter condition not equal to (!=,). Use isnotnull for the filter condition. Use functions or calculations on the index fields. When using a joint index, you need to satisfy the "best left prefix rule", otherwise it will be invalid. When using type conversion, it will also cause index failure. When using range queries, some fields of the joint index will be invalid (wh

2023-06-02 comment 0  1780

Article Introduction：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.

2022-01-05 comment 0  57482

Article Introduction：Indexes are a very important chapter for MySQL. There are also a lot of index knowledge points. If you want to master them thoroughly, you need to break down each knowledge point one by one. Today, let’s first talk about the situations that will cause index failure.

2020-11-30 comment 0  3864

Article Introduction：PHP and MySQL index failure situations and how to avoid and solve them Introduction: PHP and MySQL are often commonly used programming languages ​​and databases when developing web applications. When processing large amounts of data, indexing is one of the important factors to improve query performance. However, index failure can cause queries to slow down, impacting application performance. This article aims to introduce the failure of PHP and MySQL indexes, and provide some practical solutions and avoidance measures. 1. What is index failure? Index failure refers to the

2023-10-15 comment 0  802

Article Introduction：MySQL indexes will fail when querying without using index columns, mismatching data types, improper use of prefix indexes, using functions or expressions for querying, incorrect order of index columns, frequent data updates, and too many or too few indexes. . 1. Do not use index columns for queries. In order to avoid this situation, you should use appropriate index columns in the query; 2. Data types do not match. When designing the table structure, you should ensure that the index columns match the data types of the query; 3. , Improper use of prefix index, you can use prefix index.

2023-08-09 comment 0  9866

Article Introduction：Reasons for Oracle index failure: 1. Not using the WHERE clause; 2. Using "IS NULL" and "IS NOT NULL"; 3. Using functions in the WHERE clause; 4. Using LIKE for fuzzy queries; 5. Using WHERE Use the not equal operation in the clause; 6. Compare unmatched data types, etc.

2022-01-26 comment 0  11158