Refactoring SQL code for performance

6. loan_nbr customer_nbr code value
1 1 amount 1500.00
1 1 date 20080110
1 1 type personal
2 2 amount 3500.00
2 2 date 20080215
2 2 type personal
CREATE TABLE EAV_Loans (
loan_nbr INT NOT NULL,
customer_nbr INT NOT NULL,
code VARCHAR(30) NOT NULL,
value VARCHAR(200),
CONSTRAINT pk_eav_loans
PRIMARY KEY (loan_nbr, customer_nbr, code));

7. -- Customers with personal loans over 1000.00 for the period
-- Jan 1, 2008 through Jan 31, 2008
SELECT A.loan_nbr,
A.customer_nbr,
CAST(A.value AS DATETIME) AS loan_date,
CAST(B.value AS DECIMAL(15, 2)) AS loan_amount
FROM EAV_Loans AS A
INNER JOIN EAV_Loans AS B
ON A.loan_nbr = B.loan_nbr
AND A.customer_nbr = B.customer_nbr
INNER JOIN EAV_Loans AS C
ON A.loan_nbr = C.loan_nbr
AND A.customer_nbr = C.customer_nbr
WHERE A.code = 'date'
AND CAST(A.value AS DATETIME) >= '20080101'
AND CAST(A.value AS DATETIME) < '20080201'
AND B.code = 'amount'
AND CAST(B.value AS DECIMAL(15, 2)) > 1000.00
AND C.code = 'type'
AND C.value = 'personal';

9. SELECT A.loan_nbr,
A.customer_nbr,
loan_date,
loan_amount
FROM (SELECT loan_nbr, customer_nbr,
CAST(value AS DATETIME) AS loan_date
FROM EAV_Loans
WHERE code = 'date') AS A
INNER JOIN (SELECT loan_nbr, customer_nbr,
CAST(value AS DECIMAL(15, 2))
AS loan_amount
FROM EAV_Loans
WHERE code = 'amount') AS B
ON A.loan_nbr = B.loan_nbr
AND A.customer_nbr = B.customer_nbr
INNER JOIN (SELECT loan_nbr, customer_nbr,
value AS loan_type
FROM EAV_Loans
WHERE code = 'type') AS C
ON A.loan_nbr = C.loan_nbr
AND A.customer_nbr = C.customer_nbr
WHERE loan_date >= '20080101'
AND loan_date < '20080201'
AND loan_amount > 1000.00
AND loan_type = 'personal';

10. SELECT loan_nbr,
customer_nbr,
loan_date,
loan_amount
FROM (SELECT loan_nbr,
customer_nbr,
MAX(CASE WHEN code = 'date'
THEN CAST(value AS DATETIME) END),
MAX(CASE WHEN code = 'amount'
THEN CAST(value AS DECIMAL(15, 2)) END),
MAX(CASE WHEN code = 'type'
THEN value END)
FROM EAV_Loans
GROUP BY loan_nbr, customer_nbr
)
AS L(loan_nbr, customer_nbr, loan_date, loan_amount, loan_type)
WHERE loan_date >= '20080101'
AND loan_date < '20080201'
AND loan_amount > 1000.00
AND loan_type = 'personal';

11. loan_nbr customer_nbr loan_date loan_amount loan_type
1 1 2008-01-10 00:00:00.000 1500.00 personal
2 2 2008-02-15 00:00:00.000 3500.00 personal
CREATE TABLE Loans (
loan_nbr INT NOT NULL,
customer_nbr INT NOT NULL,
loan_date DATETIME NOT NULL,
loan_amount DECIMAL(15, 2) NOT NULL,
loan_type VARCHAR(10) NOT NULL,
CONSTRAINT ck_loan_type
CHECK (loan_type IN ('personal', 'business')),
CONSTRAINT pk_loans
PRIMARY KEY (loan_nbr));

12. -- Convert EAV table to normalized
INSERT INTO Loans
(loan_nbr, customer_nbr, loan_date, loan_amount, loan_type)
SELECT loan_nbr,
customer_nbr,
MAX(CASE WHEN code = 'date'
THEN CAST(value AS DATETIME) END),
MAX(CASE WHEN code = 'amount'
THEN CAST(value AS DECIMAL(15, 2)) END),
MAX(CASE WHEN code = 'type' THEN value END)
FROM EAV_Loans
GROUP BY loan_nbr, customer_nbr;

13. -- Customers with personal loans over 1000.00
-- for period Jan 1, 2008 through Jan 31, 2008
SELECT loan_nbr, customer_nbr, loan_date, loan_amount
FROM Loans
WHERE loan_date >= '20080101'
AND loan_date < '20080201'
AND loan_amount > 1000.00
AND loan_type = 'personal';

14. -- Replacement view for legacy code
CREATE VIEW EAV_Loans
(loan_nbr, customer_nbr, code, value)
AS
SELECT loan_nbr, customer_nbr,
CAST('date' AS VARCHAR(30)),
CONVERT(VARCHAR(200), loan_date, 112)
FROM Loans
UNION
SELECT loan_nbr, customer_nbr,
CAST('amount' AS VARCHAR(30)),
CAST(loan_amount AS VARCHAR(200))
FROM Loans
UNION
SELECT loan_nbr, customer_nbr,
CAST('type' AS VARCHAR(30)),
CAST(loan_type AS VARCHAR(200))
FROM Loans;

17. loan_nbr loan_date loan_amount loan_type rk
3 2008-03-11 00:00:00.000 5000.00 business 1
6 2008-03-27 00:00:00.000 4000.00 business 2
7 2008-04-10 00:00:00.000 3500.00 business 3
4 2008-03-12 00:00:00.000 2000.00 personal 1
8 2008-04-12 00:00:00.000 2000.00 personal 2
1 2008-01-01 00:00:00.000 1500.00 personal 3
5 2008-03-25 00:00:00.000 1200.00 personal 4
2 2008-02-15 00:00:00.000 1000.00 personal 5

18. SELECT loan_nbr, loan_date, loan_amount,
loan_type,
(SELECT COUNT(*)
FROM Loans AS L2
WHERE L2.loan_type = L1.loan_type
AND (L2.loan_amount > L1.loan_amount
OR L2.loan_amount = L1.loan_amount
AND L2.loan_nbr <= L1.loan_nbr)) AS rk
FROM Loans AS L1
ORDER BY loan_type, rk;

19. SELECT loan_nbr, loan_date, loan_amount, loan_type,
ROW_NUMBER() OVER(PARTITION BY loan_type
ORDER BY loan_amount DESC,
loan_nbr) AS rk
FROM Loans
ORDER BY loan_type, rk;

21. loan_nbr customer_nbr loan_date loan_amount loan_type
2 2 2008-02-15 00:00:00.000 1000.00 personal
3 1 2008-03-11 00:00:00.000 4500.00 business
4 3 2008-03-12 00:00:00.000 2000.00 personal
loan_nbr customer_nbr loan_date loan_amount loan_type
1 1 2008-01-01 00:00:00.000 1500.00 personal
2 2 2008-02-15 00:00:00.000 1000.00 personal
3 1 2008-03-11 00:00:00.000 5000.00 business
loan_nbr customer_nbr loan_date loan_amount loan_type
2 2 2008-02-15 00:00:00.000 1000.00 personal
3 1 2008-03-11 00:00:00.000 4500.00 business
4 3 2008-03-12 00:00:00.000 2000.00 personal

22. -- Update changed
UPDATE Loans
SET loan_amount = (SELECT D.loan_amount
FROM DailyChangedLoans AS D
WHERE D.loan_nbr = Loans.loan_nbr
AND D.loan_amount <> Loans.loan_amount)
WHERE EXISTS(SELECT *
FROM DailyChangedLoans AS D
WHERE D.loan_nbr = Loans.loan_nbr
AND D.loan_amount <> Loans.loan_amount);
-- Insert new loans
INSERT INTO Loans
(loan_nbr, customer_nbr, loan_date, loan_amount, loan_type)
SELECT loan_nbr,
customer_nbr,
loan_date,
loan_amount,
loan_type
FROM DailyChangedLoans AS D
WHERE NOT EXISTS(SELECT *
FROM Loans AS L
WHERE D.loan_nbr = L.loan_nbr);
-- Remove deleted
DELETE FROM Loans
WHERE NOT EXISTS(SELECT *
FROM DailyChangedLoans AS D
WHERE D.loan_nbr = Loans.loan_nbr);

23. -- Using a single MERGE statement
MERGE INTO Loans AS L
USING DailyChangedLoans AS D
ON D.loan_nbr = L.loan_nbr
WHEN MATCHED
AND L.loan_amount <> D.loan_amount
THEN UPDATE SET loan_amount = D.loan_amount
WHEN NOT MATCHED
THEN INSERT VALUES(D.loan_nbr,
D.customer_nbr,
D.loan_date,
D.loan_amount,
D.loan_type)
WHEN NOT MATCHED BY SOURCE
THEN DELETE;

26. loan_nbr customer_nbr loan_date loan_amount loan_type
1 1 2008-01-01 00:00:00.000 1500.00 personal
2 2 2008-01-02 00:00:00.000 1000.00 personal
3 1 2008-01-03 00:00:00.000 5000.00 business
4 3 2008-01-12 00:00:00.000 2000.00 personal
5 4 2008-01-13 00:00:00.000 1200.00 personal
6 3 2008-01-29 00:00:00.000 4000.00 business
7 5 2008-01-30 00:00:00.000 3500.00 business
8 2 2008-01-31 00:00:00.000 2000.00 personal
start_date end_date
2008-01-01 00:00:00.000 2008-01-03 00:00:00.000
2008-01-12 00:00:00.000 2008-01-13 00:00:00.000
2008-01-29 00:00:00.000 2008-01-31 00:00:00.000

27. -- Find last date for date range
-- and use as grouping factor
SELECT MIN(loan_date) AS start_date,
MAX(loan_date) AS end_date
FROM (SELECT loan_date,
(SELECT MIN(L2.loan_date)
FROM Loans AS L2
WHERE L2.loan_date >= L1.loan_date
AND NOT EXISTS
(SELECT *
FROM Loans AS L3
WHERE L3.loan_date =
DATEADD(DAY, 1, L2.loan_date))
) AS base
FROM Loans AS L1) AS L
GROUP BY base;

28. -- Preparation for solution
SELECT loan_date,
DATEDIFF(DAY, '19000101', loan_date) AS days_since_base_date,
ROW_NUMBER() OVER(ORDER BY loan_date) AS rn
FROM Loans;
loan_date days_since_base_date rn
2008-01-01 00:00:00.000 39446 1
2008-01-02 00:00:00.000 39447 2
2008-01-03 00:00:00.000 39448 3
2008-01-12 00:00:00.000 39457 4
2008-01-13 00:00:00.000 39458 5
2008-01-29 00:00:00.000 39474 6
2008-01-30 00:00:00.000 39475 7
2008-01-31 00:00:00.000 39476 8

29. -- Solution with ROW_NUMBER
SELECT MIN(loan_date) AS start_date,
MAX(loan_date) AS end_date
FROM (SELECT loan_date,
DATEDIFF(DAY, '19000101', loan_date) -
ROW_NUMBER() OVER(ORDER BY loan_date) AS base
FROM Loans) AS L
GROUP BY base;