MySQL是一種常用的關(guān)系型數(shù)據(jù)庫(kù)管理系統(tǒng),分表是在數(shù)據(jù)較大時(shí)提高查詢效率的一種常用方法,但是如何在分表后進(jìn)行排序查詢呢?下面是一些方法:
1.在不按照分表鍵排序的情況下,可以使用MySQL的union技術(shù)將每個(gè)分表的數(shù)據(jù)排序后進(jìn)行查詢,例如:
select * from (select * from table1 order by timestamp desc limit 100) t1 union all (select * from table2 order by timestamp desc limit 100) t2 order by timestamp desc limit 100;
2.如果按照分表鍵進(jìn)行排序,可以使用帶分表鍵的order by語(yǔ)句,例如:
select * from table1 order by timestamp desc, id desc limit 100;
3.如果表格按照某個(gè)字段進(jìn)行垂直分割(如大訂單表根據(jù)客戶ID拆分成幾個(gè)小表),可以通過(guò)UNION ALL語(yǔ)句將子表合并,并使用MySQL的子查詢進(jìn)行排序,例如:
select * from (select * from table1 where customer_id='123' order by timestamp desc limit 100) t1 union all (select * from table2 where customer_id='123' order by timestamp desc limit 100) t2 order by timestamp desc limit 100;
在以上方法中,關(guān)鍵在于如何將數(shù)據(jù)合并并按照要求排序,在實(shí)際操作過(guò)程中需要根據(jù)具體情況進(jìn)行選擇。