sinat_29193161的博客

通过计算选择性来确定前缀索引的选择性全列选择性：SELECT COUNT(DISTINCT column_name) / COUNT(*) FROM table_name;某一字段长度前缀的选择性SELECT COUNT(DISTINCT LEFT(column_name, prefix_length)) / COUNT(*) FROM table_name;当前缀的选择性越接近全列选择性的时候，索引效果越好...

碰到大坑。。就是因为卸载不干净brew services stop mysql@5.6brew uninstal mysql@5.6brew unlink mysql@5.6rm -rf /usr/local/bin/mysql/rm -rf /usr/local/include/mysql/rm -rf /usr/local/var/mysql/rm -rf /usr/local/Cellar/mysql@5.6/# rm -rf /usr/local/share/mysql

修改 my.ini 文件sql_mode=STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION

MySQL已启用了slow query log且long_query_time=0.01，为什么有些慢SQL还是没被记录呢？1、在线动态设置long_query_time=0.01，但该设置对当前已建立的连接不会生效2、log_slow_admin_statements=0，因此ALTER、CREATE INDEX、ANALYZE TABLE等操作即使超过long_query_time不会记录...