SQL optimization

limit Optimize

once SQL Analysis of query optimization principle （900W+ data , from 17s To 300ms）

There's a financial statement , Not divided into databases and tables , The current amount of data is 9555695, Paging query uses limit, Query time before optimization 16 s 938 ms (execution: 16 s 831 ms, fetching: 107 ms), Adjust as follows SQL after , Time consuming 347 ms (execution: 163 ms, fetching: 184 ms);

 operation ：  The query criteria are placed in the subquery , Subqueries only look up primary keys ID, Then use the primary key Association determined in the subquery to query other attribute fields ;

 principle ：  Reduce the return operation , Use delay association or subquery to optimize the super multi page scenario .

--  Before optimization SQL
SELECT   Various fields 
FROM `table_name`
WHERE  Various conditions 
LIMIT 0,10;

--  After optimization SQL
SELECT   Various fields 
FROM `table_name` main_tale
RIGHT JOIN
(
SELECT   Subqueries only look up primary keys 
FROM `table_name`
WHERE  Various conditions 
LIMIT 0,10;
) temp_table ON temp_table. Primary key  = main_table. Primary key