前言
在mysql中,多表連接查詢是很常見的需求,在使用多表查詢時,可以from多個表,也可以使用join連接連個表
這兩種查詢有什么區(qū)別?哪種查詢的效率更高呢? 帶著這些疑問,決定動手試試
1.先在本地的mysql上先建兩個表one和two
one表
| CREATE TABLE `one` ( `id` int(0) NOT NULL AUTO_INCREMENT, `one` varchar(100) NOT NULL, PRIMARY KEY (`id`)) ENGINE = InnoDB CHARACTER SET = utf8; |
two表
| CREATE TABLE `two` ( `id` int(0) NOT NULL AUTO_INCREMENT, `two` varchar(100) NOT NULL, PRIMARY KEY (`id`)) ENGINE = InnoDB CHARACTER SET = utf8; |
先隨便插入幾條數(shù)據(jù),查詢看一下;
| select one.id,one.one,two.id,two.two from one,two where one.id=two.id; |
| select one.id,one.one,two.id,two.two from one join two on one.id=two.id; |
對比這兩次的查詢,查詢時間幾乎沒有區(qū)別,查看sql運行分析,也沒有區(qū)別
為了突出兩種查詢的性能差異,往one表中插入100w條數(shù)據(jù),往two表中插入10w條數(shù)據(jù),在大量數(shù)據(jù)面前,一絲一毫的差別也會被無限放大;這時候在來比較一下差異
先使用python往數(shù)據(jù)庫中插入數(shù)據(jù),為啥用python,因為python寫起了簡單
上代碼
| import pymysqldb = pymysql.connect("127.0.0.1", 'root', "123456", "bruce")cursor = db.cursor()sql = "INSERT INTO one (one) values (%s)"for i in range(1000000): cursor.executemany(sql, ['one' + str(i)]) if i % 10000 == 0: db.commit() print(str(i) + '次 commit')db.commit()print('insert one ok')sql2 = "INSERT INTO two (two) values (%s)"for i in range(100000): cursor.executemany(sql2, ['two' + str(i)]) if i % 10000 == 0: db.commit() print(str(i) + '次 commit')db.commit()print('insert two ok') |
