MySQL optimization tips

max（）

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For example, a sql select max(money) from pay, When querying, the full table will be scanned to find out the maximum value , But if we give money Add an index , Execution efficiency will be fast , Because this is equivalent to an overlay index , Indexes are sequential , No need to scan for

count()

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count(*) The empty columns will also be calculated ,count(release_year), If you specify which field directly, the empty column will not be calculated

Sub query optimization

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Usually, the subquery is transformed into join To query , But pay attention to data duplication

limit Query optimization

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limit Usually accompanied by order by Sort , So it's going on order by When sorting fields, it is best to use indexed fields or primary keys

Index optimization

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How to select an appropriate column to create an index

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The dispersion refers to the 《 A big factory Java Analysis of interview questions + Back end development learning notes + The latest architecture explanation video + Practical project source code handout 》 Free open source Prestige search official account 【 Advanced programming 】 How many values are not repeated , The greater the dispersion , In the joint index, it should be placed in front of

Delete unused indexes and duplicate indexes

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Database table structure optimization

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Choose the right data type

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Paradigm and anti paradigm optimization

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Table vertical split

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Table split horizontally

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Horizontal splitting is to solve the problem of too much data in a single table , It can be split by modulo operation , The table structure of each table is the same , The resulting problems are query and background analysis statistics , When statistics are available, the table is summarized , Query should consider specific business scenarios for operation

System profile optimization

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innodb_buffer_pool_size