Low performance, too long execution time, too long waiting time, connection query, and index failure .
(1) Writing process
select distinct ... from ... join ... on ... where ... group by ... having ... order by ... limit ...
(2) Parsing process
from ... on ... join ... where ... group by ... having ... select distinct ... order by ... limit ...
The index is equivalent to the table of contents of the book.
The data structure of the index is a B-tree.
The above is the detailed content of Under what circumstances should sql optimization be performed in MySQL?. For more information, please follow other related articles on the PHP Chinese website!