DECODE用法：
DECODE(value,if1,then1,if2,then2,if3,then3,...,else)
含义为：
if 条件=值1 then
return(value 1)
else if 条件=值2 then
return(value 2)
......
else if 条件=值n then
return(value 3)
else
return(default)
END IF
ps：
A,B在数据库为float类型
decode(A,B,0,1) ：当A=B，返回0，否则返回1
select httz.HETONG_BIAOHAO,HETONG_ZONGJINE,heji,decode(HETONG_ZONGJINE,heji,0,1)
from t_htybz_httz httz left join (select HETONG_BIANHAO,sum(JIESUAN_HEJIA) hejifrom T_HTYBZ_WLJSDB group by HETONG_BIANHAO
) sdb
on httz.HETONG_BIAOHAO=sdb.HETONG_BIANHAO