Recently a function query was slow for a minute, so I managed to optimize it and finally optimized it to within 8 seconds.
Summary: The optimized code is mainly optimized from these parts:
1.sql
2. Code
3. Data
4. Index
<!--[if !supportLists]--> 1. <!--[endif]--> Check the execution plan through sql explain , which parts do not use indexes and which parts of sql execute slowly, and locate them carefully
<!--[if !supportLists]--> 2. <!--[endif]--> Optimize sql to minimize the use of subqueries and use join
<!--[if !supportLists]--> 3. <!--[endif]-->Check whether the speed is faster by adding an index
<!--[if !supportLists]--> 4. <!--[endif]--> If it doesn't work, see if other code is dragging down the query
<!--[if !supportLists]--> 5. <!--[endif]--> If there is no above problem, check whether there is garbage data generated in the data, resulting in data expansion
<!--[if !supportLists]--> 6. <!--[endif]--> Check the code again to see what caused the garbage data
<!--[if !supportLists]--> 7. <!--[endif]--> Mysql left join does not go to the index, pay attention to this problem