平均密度

The optimization methods of database SQL query were studied and some available query optimization Methods were given out as follows: The incompatible data type should avoid to be used; More redundancy search parameters should be given as join condition in join query; In some condition, the number of note hitted to target was estimated by optimizing implement using the average density; Some other maths operating symbol should avoid to be used as condition parameters in WHERE clause; Some operating symbol and its sentence should avoid to be used also; When the cluster function was used,the WHERE clause should be paied attention to more,and so on.

作者单位：（重庆工学院商贸信息学院，重庆 400050）摘要：数据库SQL查询语句的优化，须注意：避免使用不兼容数据类型；连接查询中应多给连接条件提供一些冗余的搜索参数；某种条件下优化器只能使用其平均密度以估计命中的记录数；避免对WHERE子句中条件参数使用其它数学操作符；避免使用某些操作符及相应语句；聚簇函数的使用应注意WHERE子句。

And the number of species and mean density showed seasonal tendencies.

该水域仔稚鱼的种类和平均密度具有季节性变化趋势。

Galaxies, for instance, are 106 times more dense than the universe's mean density.

比如星系，其密度比宇宙的平均密度要大100万倍。

The incidence relative intensity and mean density of infection fluctuated irregularly in different month in a year.

不同月份中外栉绕宫吸虫在宿主肠道内的感染率、感染强度和种群平均密度没有明显的变化规律。

The main results are as follows: 1. From the specimens we observed 5 phyla 53 genus 106 species of phytoplankton. The mean density and biomass of phytoplankton are 80.954xl04 ind/L and 0.567 mg/L.

结果如下： 1。样品中共检出浮游植物5门53属106种，浮游植物的平均密度和生物量分别为80.954×10~4 ind／L和0.567 mg／L。

The results indicated that the mean density of sperm was (1.17±0.09)×10^10ml^(-1) and the vitality was greatly affected by different salinities.

试验结果表明：精子平均密度为(1.17±0.09)×10^10ml^(-1)，盐度对大黄鱼精子活力影响较大。

Wet lung disease of neonatal ; Spiral CT ; Lung mean density ; Diagnosis

新生儿湿肺症；螺旋CT ；肺平均密度值；诊断

Beds of less than normal density are slightly uplifted.

低于平均密度的地面微微隆起。

Q.19 What is your Double Occupancy Factor?

问题19：全年每间客房的平均住客人数/平均密度（全年住客总人数除以全年出租客房间夜总数）？

"Its mean density is only about 0.2 grams per cubic centimeter, or about the density of balsa wood," said study leader Georgi Mandushev of the Lowell Observatory in Arizona.

&其平均密度只有约每平方厘米0.2克，或者说相当于轻质木材的密度，&研究小组组长、亚利桑那州洛厄尔天文台的乔吉·曼德舍夫说，&由于该行星对上层大气的引力相对较小，很可能其中部分大气呈慧尾状而逃逸掉。&

I didn't watch TV last night, because it .

昨晚我没有看电视，因为电视机坏了。

Since this year, in a lot of villages of Beijing, TV of elevator liquid crystal was removed.

今年以来，在北京的很多小区里，电梯液晶电视被撤了下来。