Database nesting queries

:) Off-Topic

Long time no writing essays recently always for other things to worry about reverse telecommuting emotional problems and mood is low and so bad mood is not easy to get sick yesterday burned a day well all over the family is my all want to support me and bring me a large part of the pressure of the program Monkey Baby or a lot of improve themselves bar (old?????? ) Old

Select t1.*,
Case when coalesce (T2. score,0) = 0 Then 0 else
round (t1. Score-t2.score)/t2. score*100,2) End SCORE_HB,//Condition: The current field is not empty and is not 0 o'clock, you can perform a chain operation
Case when COALESCE (T2. analyze_delay,0) = 0 Then 0 else
Round (t1. Analyze_delay-t2.analyze_delay)/t2. analyze_delay*100,2) End ANALYZE_DELAY_HB,
Case when COALESCE (T2. link_delay,0) = 0 Then 0 else
Round (t1. Link_delay-t2.link_delay)/t2. link_delay*100,2) End LINK_DELAY_HB,
Case when COALESCE (T2. first_get_delay,0) = 0 Then 0 else
Round (t1. First_get_delay-t2.first_get_delay)/t2. first_get_delay*100,2) End FIRST_GET_DELAY_HB,
Case when COALESCE (T2. first_page_delay,0) = 0 Then 0 else
Round (t1. First_page_delay-t2.first_page_delay)/t2. first_page_delay*100,2) End FIRST_PAGE_DELAY_HB,
Case when COALESCE (T2. download_rate,0) = 0 Then 0 else
Round (t1. Download_rate-t2.download_rate)/t2. download_rate*100,2) End DOWNLOAD_RATE_HB,
Case when COALESCE (T2. webload_delay,0) = 0 Then 0 else
Round (t1. Webload_delay-t2.webload_delay)/t2. webload_delay*100,2) End WEBLOAD_DELAY_HB,
Case when COALESCE (T2. total_delay,0) = 0 Then 0 else
Round (t1. Total_delay-t2.total_delay)/t2. total_delay*100,2) End TOTAL_DELAY_HB,
Case when COALESCE (T2. download_delay,0) = 0 Then 0 else
Round (t1. Download_delay-t2.download_delay)/t2. download_delay*100,2) End DOWNLOAD_DELAY_HB,
Case when COALESCE (T2. analyze_suc_rate,0) = 0 Then 0 else
Round (t1. Analyze_suc_rate-t2.analyze_suc_rate)/t2. analyze_suc_rate*100,2) End ANALYZE_SUC_RATE_HB,
Case when COALESCE (T2. link_suc_delay,0) = 0 Then 0 else
Round (t1. Link_suc_delay-t2.link_suc_delay)/t2. link_suc_delay*100,2) End LINK_SUC_DELAY_HB,
Case when COALESCE (T2. download_size,0) = 0 Then 0 else
Round (t1. Download_size-t2.download_size)/t2. download_size*100,2) End DOWNLOAD_SIZE_HB,
Case when COALESCE (T2. useable_rate,0) = 0 Then 0 else
Round (t1. Useable_rate-t2.useable_rate)/t2. useable_rate*100,2) End USEABLE_RATE_HB
From

(SELECT
Day_key,
City_key,
Oper_key,
App_type_key,
App_subtype_key,
Host_key,
round (score,2) as score,//To define aliases for data columns after any processing
Analyze_delay,
Link_delay,
First_get_delay,
First_page_delay,
Download_rate,
Webload_delay,
Total_delay,
Download_delay,
Round (analyze_suc_rate,2) as Analyze_suc_rate,
Link_suc_delay,
Download_size,
Round (useable_rate,2) as Useable_rate,
Num
From Dw_ft_web_city_l2_dy
where 1=1
$[and City_key = (: {city})]
$[and Day_key = (: {time})]) t1

Left join //Correlation query
(
Select
Day_key,
City_key,
Oper_key,
App_type_key,
App_subtype_key,
Host_key,
Round (score,2) as score,
Analyze_delay,
Link_delay,
First_get_delay,
First_page_delay,
Download_rate,
Webload_delay,
Total_delay,
Download_delay,
Round (analyze_suc_rate,2) as Analyze_suc_rate,
Link_suc_delay,
Download_size,
Round (useable_rate,2) as Useable_rate,
Num
From Dw_ft_web_city_l2_dy
where 1=1
$[and City_key = (: {city})]
$[and Day_key = To_number (To_char (To_date (': {time} ', ' YyyyMMdd ')-1, ' YYYYMMDD ')]) T2
on T1. City_key=t2. City_key and T1. Oper_key=t2. Oper_key

Database nesting queries