SQL性能优化 Customer表定义如下 CREATE TABLE `test01` (     custid` int(10) NOT NULL,     custname` varchar(100) NOT NULL,     date` datetime default NULL,     money` int(10) default NULL,     PRIMARY KEY  (`custid`),     KEY `index_test01_custname` (`custname`),     KEY `index_test01_custname_union` (`money`,` date`,`custname`,), ) secondinfo 表定义如下 CREATE TABLE `test02` (   secid` int(10) NOT NULL,   firstid` int(10) NOT NULL,   custid` int(10) default NULL,   PRIMARY KEY (`secid`),   KEY `Index_test02_custid` (`custid `) ) 下列SQL执行速度比较慢，请分析原因并做优化： 1)    SELECT  *  FROM  test01  WHERE  substring(custname,1,4)='beizhi'; 2)    SELECT  *  FROM  test01  WHERE  money/30<1000;  3)    SELECT  *  FROM  test01  WHERE  custname=3721;  4)    SELECT * FROM test02 s WHERE s.custid NOT IN (SELECT c.custid FROM test01 c); 5)    select * from test01 where money<1000 union select * from test01 where date >’20150101’;