mysql tuning

mysql tuning
One: Avoid full table scan in where   order by involves field setting index
     1. Avoid using it in where condition ! =  >  < , otherwise the engine will give up using the index and perform a full table scan.
    2. Avoid the where condition to judge null, otherwise the engine will give up the use of the index and perform a full table scan.
        You can set null to 0 to indicate
     3. The where condition avoids or to judge, otherwise the engine will give up the use of the index and perform a full table scan.
        select id from tablename where name = ' Tom '  or name = ' Que '   Error

        select id from tablename where name = ' Tom '  union  all (union query)
         select id from tablename where name = ' Que '                 True
     4 . Do not use fuzzy query, otherwise the engine will give up using the index and perform a full table scan.
        select id from tablename where  like  ' %ang% ' Error
        To improve efficiency, consider full-text search.
    5.in  not in用法
        select id from tablename where score in(90,91,92) Error
        For consecutive numbers you can use between
        select id from tablename where score between  90  and  91 
    6. Avoid modifying the value of the field, otherwise the engine will give up using the index and perform a full table scan.
        select name from tablename where score + 1 = 60      Error
         select name from tablename where score = 60 - 1         True
          where condition ' = ' If the function expression cannot be calculated on the left side, the engine will give up using the index and perform a full table scan.        
             -- Try to avoid functional operations on fields in the where statement
    7. Many times using exists instead of in is a good choice
         select name from tablename wherer name in ( select name from tablename1) Erroe
         select name from tablename where  exists ( select name from tablename1 where name = tablename.name) True