数据库学习

SQL及索引优化
如何发现有问题的SQL？
使用MySQL慢查日志对有效率问题的SQL进行监控
show variables like 'slow_query_log'
set global slow_query_log_file=‘/home/mysql/sql_log/mysql-slow.log'
set global log_queries_not_using_indexes=on；
set global long_query_time=1

mysql查询表是否存在：
SELECT table_name FROM information_schema.TABLES WHERE table_name ='am_no_meter_reading_2014';

SELECT COUNT(*) FROM information_schema.TABLES WHERE LCASE(table_name)='am_no_meter_reading_2014'

 SELECT  COUNT(1) FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA='ysy_ammeter' AND TABLE_NAME=#{tableName}