mysql group by 字段多,怎么优化?
比如现在有个sql语句是这样的:select count(score) from students group by school_name,grade,student_name
students里面大概一百万条数据,怎么添加索引才能优化查询?
mysql
mysql优化
mysql索引
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待解决
给
school_name,grade,student_name
做个索引就完事了