我有一个包含varchar（6），datetime和两个浮点数的表。它有超过3000万条记录
varchar和datetime用作具有超过500k记录的表的连接条件，以及结果中使用的两个浮点数的总和和平均值。
我正在接受索引建议以加快速度。
有112个唯一的varchar值，以及525k个唯一的日期时间值。
加入条件为import javax.swing.JOptionPane;
public class Temp3 {
public static void main(String[] args) {
// String sentence = "This is a Java program for converting
// temperatures.";
String [] options = {"Convert from Celsius to fahrenheit", "Convert from Fahrenheit to Celsios","Exit"};
int choice=0;
do{ //do while is used so that the loop will run AT LEAST ONCE
choice = JOptionPane.showOptionDialog(null,"What do you want to do?",
"Choose an option", JOptionPane.YES_NO_CANCEL_OPTION, //option type
JOptionPane.QUESTION_MESSAGE,
null, options, options[0]);
convertTemp(choice);
}while(choice!=2);
}
private static void convertTemp(int choice) {
// TODO Auto-generated method stub
String from = "", to = "";
if(choice==0){ //set to and form so that you don't need to type the units again and again
from="Celsius";
to ="Fahrenheit";
}else if(choice==1){
to="Celsius";
from ="Fahrenheit";
}else{
JOptionPane.showMessageDialog(null,"Goodbye","Exit",JOptionPane.INFORMATION_MESSAGE);
//I often put message type to make it more presentable
return; //exit method :)
}
Float tempFrom= Float.parseFloat(JOptionPane.
showInputDialog("You are now converting from "+from+" to "+ to+"."
+ "Please enter degrees in "+from +".")); //get input
while(tempFrom<-100 ||tempFrom>100){ //check if input is valid
if(tempFrom>100){
tempFrom = Float.parseFloat(JOptionPane.showInputDialog(null, "That number is too high. "
+ "Please enter a temperature between -100 & 100 degress "+from , "Temperature too high"
, JOptionPane.ERROR_MESSAGE));//inform the user about the error and ask for the input at the same time
}else{
tempFrom = Float.parseFloat(JOptionPane.showInputDialog(null, "That number is too low. "
+ "Please enter a temperature between -100 & 100 degress "+from , "Temperature too low"
, JOptionPane.ERROR_MESSAGE));//inform the user about the error and ask for the input at the same time
}
}
double answer =0;
if(choice==0){ //celsius to fahrenheit
answer = (tempFrom * 1.8) + 32;
}else{ //fahrenheit to celsius
answer = (tempFrom- 32) / 1.8;
}
JOptionPane.showMessageDialog(null, "The temperature in "+ to +" is " +
answer
,to,
JOptionPane.INFORMATION_MESSAGE);
}
}
我一直在玩聚类，非聚簇，复合和覆盖索引的各种组合，但我不是真正的专家，所以我很欣赏人们的意见。
我的主要问题是这里首选的聚集或非聚集索引，为什么？覆盖指数更好，为什么？
我在改变事物的过程中看到了对执行路径的各种更改，但我不知道具有嵌套循环的Eager Index Spool是否优于散列匹配。
欢呼任何帮助。