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This article mainly explains "what are the reasons for the slow execution of SQL statements". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what are the reasons for the slow execution of SQL statements?"

A SQL statement executes slowly in two cases:

Most cases are normal, sometimes very slow.

1. When the database is busy with data, updates or new data will be temporarily recorded in the redo log log, and when it is free, the data will be synchronized to disk. Assuming that the database has been busy, updated frequently, and the redo log is full, we have to pause other operations to synchronize data to disk, which may cause our SQL statements to execute very slowly.

2. Table lock row lock is encountered during execution. When others use table or row data to lock the database, they can only slowly wait for others to release the lock.

This SQL statement has been slow.

1. No index is used, for example, the field does not use an index

2. Due to the operation of the field, the function operation does not use the index.

3. Database sampling prediction index foundation error, resulting in the system did not go to the index, but to take the full table scan

Thank you for your reading, the above is "what are the reasons for the slow execution of SQL statements?" after the study of this article, I believe you have a deeper understanding of the reasons for the slow execution of SQL statements, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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