Brief description of SQL optimization problems

SQL Optimization of the 7 In terms of

1. Create index
2. Avoid index invalidation
3. Lock granularity （ Row lock or watch lock ）
4. Paging query optimization
5. Avoid querying all fields
6. analysis SQL Implementation plan of
7. show profile analysis SQL Execution performance

Create index

• It is forbidden to create a separate index for each column in a table
• Every Innodb Table must have a primary key
• Pay attention to the field order of the combined index
• Override index first
• Avoid using foreign key constraints

Avoid index invalidation （ Failure scenario ）

• With % At the beginning LIKE Inquire about
• Operations on index columns , function upper() etc. ,or、!=、<>、not in wait
• Composite index created , But the query conditions are not satisfied “ The leftmost match ” principle
• Use... In query conditions or, And or There is no condition in the index before and after , Then the indexes involved will not be used

Lock granularity （ Row lock   still   Table locks ）

• MySQL Our storage engines fall into two broad categories ： MyISAM and InnoDB 
• MyISAM Only supported Table locks
• InnoDB Support Row lock and Table locks
• update operation when , In order to ensure the accuracy of table data , Usually Lock , In order to improve the high concurrency of the system , We usually recommend Row lock , Reduce lock conflicts 、 Lock wait time . therefore , Storage engines usually choose InnoDB

Paging query optimization

Avoid querying all fields

analysis SQL Implementation plan of

show profile analysis SQL Execution performance

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The follow-up will gradually improve ... Make a point in this chapter first