How to calculate a bank's deposit growth from one call report to the next, as a percentage? - google-bigquery

Question

I downloaded the entire FDIC bank call reports dataset, and uploaded it to BigQuery.
The table I currently have looks like this:
What I am trying to accomplish is adding a column showing the deposit growth rate since the last quarter for each bank:
Note:The first reporting date for each bank (e.g. 19921231) will not have a "Quarterly Deposit Growth". Hence the two empty cells for the two banks.
I would like to know if a bank is increasing or decreasing its deposits each quarter/call report (viewed as a percentage).
e.g. "On their last call report (19921231)First National Bank had deposits of 456789 (in 1000's). In their next call report (19930331)First National bank had deposits of 567890 (in 1000's). What is the percentage increase (or decrease) in deposits"?
This "_%_Change_in_Deposits" column would be displayed as a new column.
This is the code I have written so far:
select
SFRNLL.repdte, SFRNLL.cert, SFRNLL.name, SFRNLL.city, SFRNLL.county, SFRNLL.stalp, SFRNLL.specgrp AS `Loan_Specialization`, SFRNLL.lnreres as `_1_to_4_Residential_Loans`, AL.dep as `Deposits`, AL.lnlsnet as `loans_and_leases`,
IEEE_DIVIDE(SFRNLL.lnreres, AL.lnlsnet) as SFR2TotalLoanRatio
FROM usa_fdic_call_reports_1992.All_Reports_19921231_1_4_Family_Residential_Net_Loans_and_Leases as SFRNLL
JOIN usa_fdic_call_reports_1992.All_Reports_19921231_Assets_and_Liabilities as AL
ON SFRNLL.cert = AL.cert
where SFRNLL.specgrp = 4 and IEEE_DIVIDE(SFRNLL.lnreres, AL.lnlsnet) <= 0.10
UNION ALL
select
SFRNLL.repdte, SFRNLL.cert, SFRNLL.name, SFRNLL.city, SFRNLL.county, SFRNLL.stalp, SFRNLL.specgrp AS `Loan_Specialization`, SFRNLL.lnreres as `_1_to_4_Residential_Loans`, AL.dep as `Deposits`, AL.lnlsnet as `loans_and_leases`,
IEEE_DIVIDE(SFRNLL.lnreres, AL.lnlsnet) as SFR2TotalLoanRatio
FROM usa_fdic_call_reports_1993.All_Reports_19930331_1_4_Family_Residential_Net_Loans_and_Leases as SFRNLL
JOIN usa_fdic_call_reports_1993.All_Reports_19930331_Assets_and_Liabilities as AL
ON SFRNLL.cert = AL.cert
where SFRNLL.specgrp = 4 and IEEE_DIVIDE(SFRNLL.lnreres, AL.lnlsnet) <= 0.10
The table looks like this:
Additional notes:
I would also like to view the last column (SFR2TotalLoansRatio) as a percentage.
This code runs correctly, however, previously I was getting a "division by zero" error when attempting to run 50,000 rows (1992 to the present).

Answer 1

Addressing each of your question individually.
First) Retrieving SFR2TotalLoanRatio as percentage, I assume you want to see 9.988% instead of 0.0988 in your results. Currently, in BigQuery you can achieve this by casting the field into a STRING then, concatenating the % sign. Below there is an example with sample data:
WITH data as (
SELECT 0.0123 as percentage UNION ALL
SELECT 0.0999 as percentage UNION ALL
SELECT 0.3456 as percentage
)
SELECT CONCAT(CAST(percentage*100 as String),"%") as formatted_percentage FROM data
And the output,
Row formatted_percentage
1 1.23%
2 9.99%
3 34.56%
Second) Regarding your question about the division by zero error. I am assuming IEEE_DIVIDE(arg1,arg2) is a function to perform the division, in which arg1 is the divisor and arg2 is the dividend. Therefore, I would adivse your to explore your data in order to figured out which records have divisor equals to zero. After gathering these results, you can determine what to do with them. In case you decide to discard them you can simply add within your WHERE statement in each of your JOINs: AL.lnlsnet = 0. On the other hand, you can also modify the records where lnlsnet = 0 using a CASE WHEN or IF statements.
UPDATE:
In order to add this piece of code your query, you u have to wrap your code within a temporary table. Then, I will make two adjustments, first a temporary function in order to calculate the percentage and format it with the % sign. Second, retrieving the previous number of deposits to calculate the desired percentage. I am also assuming that cert is the individual id for each of the bank's clients. The modifications will be as follows:
#the following function MUST be the first thing within your query
CREATE TEMP FUNCTION percent(dep INT64, prev_dep INT64) AS (
Concat(Cast((dep-prev_dep)/prev_dep*100 AS STRING), "%")
);
#followed by the query you have created so far as a temporary table, notice the the comma I added after the last parentheses
WITH data AS(
#your query
),
#within this second part you need to select all the columns from data, and LAG function will be used to retrieve the previous number of deposits for each client
data_2 as (
SELECT repdte, cert, name, city, county, stalp, Loan_Specialization, _1_to_4_Residential_Loans,Deposits, loans_and_leases, SFR2TotalLoanRatio,
CASE WHEN cert = lag(cert) OVER (PARTITION BY id ORDER BY d) THEN lag(Deposits) OVER (PARTITION BY id ORDER BY id) ELSE NULL END AS prev_dep FROM data
)
SELECT repdte, cert, name, city, county, stalp, Loan_Specialization, _1_to_4_Residential_Loans,Deposits, loans_and_leases, SFR2TotalLoanRatio, percent(Deposits,prev_dep) as dept_growth_rate FROM data_2
Note that the built-in function LAG is used together with CASE WHEN in order to retrieve the previous amount of deposits per client.