Untitled
Let’s break down the provided SQL query step by step to understand how it works. The query is designed to calculate the sum of tiv_2016
for policyholders who meet two specific conditions:
- They share the same
tiv_2015
value with at least one other policyholder. - Their
(lat, lon)
location is unique (i.e., no other policyholder shares the same location).
The query uses Common Table Expressions (CTEs) to simplify the logic. Here’s a detailed explanation of each part:
1. unique_locations
CTE
WITH unique_locations AS ( SELECT lat, lon FROM Insurance GROUP BY lat, lon HAVING COUNT(*) = 1 )
Purpose:
This CTE identifies all unique (lat, lon)
pairs in the Insurance
table. A location is considered unique if it appears only once in the table.
How it works:
- The
GROUP BY lat, lon
groups rows by their(lat, lon)
pairs. - The
HAVING COUNT(*) = 1
filters the groups to include only those where the count of rows is exactly 1. This ensures that only unique locations are selected.
Output:
A list of (lat, lon)
pairs that appear only once in the Insurance
table.
2. shared_tiv_2015
CTE
shared_tiv_2015 AS ( SELECT tiv_2015 FROM Insurance GROUP BY tiv_2015 HAVING COUNT(*) > 1 )
Purpose:
This CTE identifies all tiv_2015
values that are shared by at least two policyholders.
How it works:
- The
GROUP BY tiv_2015
groups rows by theirtiv_2015
values. - The
HAVING COUNT(*) > 1
filters the groups to include only those where the count of rows is greater than 1. This ensures that onlytiv_2015
values shared by multiple policyholders are selected.
Output:
A list of tiv_2015
values that appear more than once in the Insurance
table.
3. Main Query
SELECT ROUND(SUM(tiv_2016)::numeric, 2) AS tiv_2016 FROM Insurance WHERE tiv_2015 IN (SELECT tiv_2015 FROM shared_tiv_2015) AND (lat, lon) IN (SELECT lat, lon FROM unique_locations);
Purpose:
This part of the query calculates the sum of tiv_2016
for policyholders who meet both conditions:
- Their
tiv_2015
value is shared with at least one other policyholder. - Their
(lat, lon)
location is unique.
How it works:
-
Filtering by
tiv_2015
:- The
WHERE tiv_2015 IN (SELECT tiv_2015 FROM shared_tiv_2015)
condition ensures that only policyholders with ativ_2015
value that appears in theshared_tiv_2015
CTE are included. These are policyholders who share theirtiv_2015
value with at least one other policyholder.
- The
-
Filtering by Unique Locations:
- The
AND (lat, lon) IN (SELECT lat, lon FROM unique_locations)
condition ensures that only policyholders with a unique(lat, lon)
pair (as identified in theunique_locations
CTE) are included.
- The
-
Summing and Rounding
tiv_2016
:- The
SUM(tiv_2016)
calculates the totaltiv_2016
for all policyholders who meet the above conditions. - The
ROUND(SUM(tiv_2016)::numeric, 2)
rounds the sum to two decimal places.
- The
Output:
The query returns a single value: the sum of tiv_2016
for all policyholders who meet the criteria, rounded to two decimal places.
Example Walkthrough
Input Table (Insurance
):
pid | tiv_2015 | tiv_2016 | lat | lon |
---|---|---|---|---|
1 | 224.17 | 952.73 | 32.4 | 20.2 |
2 | 224.17 | 900.66 | 52.4 | 32.7 |
3 | 824.61 | 645.13 | 72.4 | 45.2 |
4 | 424.32 | 323.66 | 12.4 | 7.7 |
5 | 424.32 | 282.9 | 12.4 | 7.7 |
6 | 625.05 | 243.53 | 52.5 | 32.8 |
7 | 424.32 | 968.94 | 72.5 | 45.3 |
8 | 624.46 | 714.13 | 12.5 | 7.8 |
9 | 425.49 | 463.85 | 32.5 | 20.3 |
10 | 624.46 | 776.85 | 12.4 | 7.7 |
Step 1: unique_locations
CTE
- Identifies unique
(lat, lon)
pairs:(32.4, 20.2)
(52.4, 32.7)
(72.4, 45.2)
(52.5, 32.8)
(12.5, 7.8)
(32.5, 20.3)
Step 2: shared_tiv_2015
CTE
- Identifies shared
tiv_2015
values:224.17
(shared by pid 1 and 2)424.32
(shared by pid 4, 5, and 7)624.46
(shared by pid 8 and 10)
Step 3: Main Query
- Filters policyholders who:
- Have
tiv_2015
in(224.17, 424.32, 624.46)
. - Have a unique
(lat, lon)
pair.
- Have
- Sums their
tiv_2016
values and rounds the result to two decimal places.
Output:
tiv_2016 |
---|
8206.2 |
Key Points
- CTEs Simplify Logic: The use of CTEs (
unique_locations
andshared_tiv_2015
) makes the query modular and easier to understand. - Filtering Conditions: The
WHERE
clause ensures that only policyholders who meet both conditions are included in the final calculation. - Rounding: The
ROUND
function ensures the result is formatted to two decimal places.
This query is efficient and correctly solves the problem as described. Let me know if you have further questions!