1.对于硬编码的解决方法：
在类所需要引用用的类，采用在构造器其中设置参数为接口
两个Integer不能直接比较值
2.((Integer)session).intValue() == ((Integer)str).intValue()
要用上面的方法比较session和str的值（都是Integer类型的）
3.注意map中不能有key相同的值，否则会取得
4.sql中select的结果集作为新的查询“表”
SELECT
abc.ID,ab.COMPANY_ID
FROM
(
SELECT DISTINCT
a.ID
FROM
accident_measure a,
company com
WHERE
a.ID = 1
) abc,
accident_measure ab
实例2：
StringBuffer sql=new StringBuffer("select t.uId AS userId, t.uName AS name, t.cName AS clsName, t.stuNum AS stuNum, ")
.append(" t.SCORE AS score, t.TOP AS top, t.END_TIME AS endTime , t.testStatus AS studnetTestStatus, t.approveStatus AS approveStatus")
.append(" from ( select t1.uId, t1.uName, t1.cId,t1.cName, t1.stuNum, t2.SCORE, CASE WHEN t2.top IS NULL THEN 10000 ELSE t2.top END AS TOP,")
.append(" t2.END_TIME, t2.testStatus, t2.approveStatus from ( select us.id AS uId, us.`NAME` AS uName,c.ID as cId, c.CLS_NAME AS cName,")
.append(" stu.STU_NUM AS stuNum from tb_class c, tb_student stu, tb_user us, tb_test_paper_class tpc WHERE tpc.EXAM_ID =? ")
.append(" AND tpc.CLASS_ID = c.ID AND c.ID = stu.CLASS_ID AND stu.USER_ID = us.ID and us.STATUS=0 ) t1 ")
.append(" LEFT JOIN ( select us.id AS uId, us.`NAME` AS uName, c.CLS_NAME AS cName, stu.STU_NUM AS stuNum, tc.SCORE AS SCORE,")
.append(" tc.TOP AS top, tc.END_TIME END_TIME, tc.TEST_STATUS testStatus, tc.APPROVE_STATUS approveStatus from tb_test_score tc,")
.append(" tb_student stu, tb_class c, tb_user us WHERE tc.EXAM_ID =? AND tc.STU_ID = us.ID AND us.ID = stu.USER_ID ")
.append(" AND stu.CLASS_ID = c.ID ) t2 ON t1.uid = t2.uid ) t where 1=1 ");
5.mysql中解决查询某个表时不能修改该表问题
UPDATE company c
SET c.`NAME` = 'abcdef'
WHERE
c.ID = (
SELECT abc.ID FROM(
SELECT DISTINCT a.ID FROM accident_measure a, company com WHERE a.ID = 1 ) abc
)
引入一个“中间表”，这种方式的效率应该不怎么高，可以查分成多个sql实现该功能。
6.声明一个变量接收这个查询的值,在sql后面用来计算
SELECT
@examCount \:= (
SELECT
COUNT(1) Complete
FROM
tb_test_score tb1,
tb_exam_manage tb2,
tb_test_paper tb3,
tb_user tb4,
tb_student tb5
WHERE
tb1.EXAM_ID = tb2.ID
AND tb2.TEST_PAGE_ID = tb3.ID
AND tb1.STU_ID = tb4.ID
AND tb1.CLASS_ID = tb5.CLASS_ID
AND tb1.STU_ID = tb5.USER_ID
AND tb4. STATUS = 0
AND tb1.EXAM_ID =?
AND tb1.CLASS_ID = t1.CLASS_ID
) Complete,
count(1) -@examCount Notfinished
FROM
tb_student t1,
tb_user t2
WHERE
t1.CLASS_ID =?
AND t1.USER_ID = t2.ID
AND t2. STATUS = 0
实例2：
SELECT
address,@tes := (SELECT m.id FROM modeltest m where m.id=1) testde
FROM
modeltest
WHERE @tes>0