|
|
Wed Feb 01 02:37:46 GMT 2023 Note of SQL performance tuningNote of this book - http://www.ocelot.ca/tuning.htm 1) Order of "and" and "or" is matter, if no cost-base optimizer where column1 = 'a' and column2 = 'b' -> where column2 = 'b' and column1 = 'a' if column2 'b' is less likely 2) <> is more expensive than = 3) Can force to use index if SELECT * FROM table WHERE indexed_column > 0 4) UPPER(column) might lose information, use LOWER is better 5) WHERE column = 'WORD' or column = 'word' is always faster than WHERE LOWER(column) = 'word' , even faster version is test if database if case-insensitive: WHERE column = 'WORD' or ('WORD' <> 'word' AND column = 'word') 6) 32bit integer is the fastest datatype for 32bit OS 7) column in (?, ?) is faster than column =? or column = ? for some database, and don't slow in any database 8) For aggregate functions, prevent using having, try to use fewer columns in group by and use subquery if possible 9) In fact, count(1) is not faster than count(*) 10) CAST before aggregate function: SELECT CAST(SUM(column) AS INT) -> SELECT SUM(CAST(column as INT)) 11) Use constant as much as possible, e.g.: select * from t1, t2 where t1.c1 = t2.c1 and t1.c1 = 1 -> select * from t1, t2 where t1.c1=1 andn t2.c1=1 12) Information of Join vs Subqueries 13) Information of optimum column type (VARCHAR, TIMESTAMP, WORD size INT and CHAR(1) usually better), shift effect for page 14) prevent NULL for porting issue 15) Low level table physical information Some related links - http://www.techartifact.com[..]9/12/sql-optimization-tipsquestions.html 16) Prevent database level transaction, prevent joining, prevent locking ( like auto increment key ), pretty good suggestion - http://www.aviransplace.com/2015/08/12/mysql-is-a-great-nosql/ 17) Reduce dataset for aggregation - https://www.periscopedata.com[..]-subqueries-to-count-distinct-50x-faster Few good tips, like avoid cursors - http://www.javaworld.com[..]ent/21-rules-for-faster-sql-queries.html 7 Tips for Query Optimization in SQL Servers - https://learningdaily.dev[..]optimization-in-sql-servers-fb3653c910f1 (google search) (amazon search) second |