Solutions:

1.
SELECT 
  Sale_ID, 
  Date,
  EXTRACT(YEAR FROM Date) AS Year,
  EXTRACT(MONTH FROM Date) AS Month,
  EXTRACT(DAY FROM Date) AS Day
FROM Sales_Transactions;

2.
SELECT 
  Sale_ID, 
  Date,
  DAYNAME(Date) AS Day_Of_Week
FROM Sales_Transactions
WHERE DAYOFWEEK(Date) IN (1, 7);

3.
SELECT 
  Sale_ID, 
  Date,
  DATEDIFF(CURRENT_DATE, Date) AS Days_Since_Sale
FROM Sales_Transactions;

4.
SELECT 
  s.SKU_Code, 
  p.Design_No, 
  s.Date
FROM Sales_Transactions s
JOIN Products p ON s.SKU_Code = p.SKU_Code
WHERE EXTRACT(MONTH FROM s.Date) BETWEEN 4 AND 6;

5.
SELECT 
  Operation_ID, 
  Operation_Type, 
  Date
FROM Warehouse_Ops
WHERE Date >= DATEADD(day, -30, CURRENT_DATE);

6.
SELECT 
  DAYNAME(Date) AS Day_Of_Week,
  AVG(Gross_Amount) AS Avg_Sales
FROM Sales_Transactions
GROUP BY DAYNAME(Date), DAYOFWEEK(Date)
ORDER BY DAYOFWEEK(Date);

7.
WITH CustomerDates AS (
  SELECT DISTINCT
    Customer_ID,
    Date
  FROM Sales_Transactions
),
ConsecutivePurchases AS (
  SELECT 
    Customer_ID,
    Date,
    LAG(Date) OVER (PARTITION BY Customer_ID ORDER BY Date) AS Prev_Date
  FROM CustomerDates
)
SELECT 
  c.Customer_ID,
  c.Customer_Name,
  CONCAT(cp.Date, ', ', cp.Prev_Date) AS Purchase_Dates
FROM ConsecutivePurchases cp
JOIN Customers c ON cp.Customer_ID = c.Customer_ID
WHERE DATEDIFF(cp.Date, cp.Prev_Date) = 1;

8.
WITH MonthlyProductSales AS (
  SELECT 
    SKU_Code,
    EXTRACT(MONTH FROM Date) AS Month,
    SUM(Gross_Amount) AS Monthly_Sales,
    RANK() OVER (PARTITION BY SKU_Code ORDER BY SUM(Gross_Amount) DESC) AS Sales_Rank
  FROM Sales_Transactions
  GROUP BY SKU_Code, EXTRACT(MONTH FROM Date)
)
SELECT 
  m.SKU_Code,
  m.Month AS Peak_Month,
  m.Monthly_Sales
FROM MonthlyProductSales m
WHERE m.Sales_Rank = 1;

9.
WITH InboundOps AS (
  SELECT SKU_Code, Date AS Inbound_Date
  FROM Warehouse_Ops
  WHERE Operation_Type = 'Inbound'
),
OutboundOps AS (
  SELECT SKU_Code, Date AS Outbound_Date
  FROM Warehouse_Ops
  WHERE Operation_Type = 'Outbound'
)
SELECT 
  i.SKU_Code,
  i.Inbound_Date,
  o.Outbound_Date,
  DATEDIFF(o.Outbound_Date, i.Inbound_Date) AS Days_In_Warehouse
FROM InboundOps i
JOIN OutboundOps o ON i.SKU_Code = o.SKU_Code;

10.
WITH YearlySales AS (
  SELECT 
    EXTRACT(MONTH FROM Date) AS Month,
    EXTRACT(YEAR FROM Date) AS Year,
    SUM(Gross_Amount) AS Yearly_Sales,
    LAG(SUM(Gross_Amount)) OVER (PARTITION BY EXTRACT(MONTH FROM Date) ORDER BY EXTRACT(YEAR FROM Date)) AS Previous_Year_Sales
  FROM Sales_Transactions
  GROUP BY EXTRACT(MONTH FROM Date), EXTRACT(YEAR FROM Date)
)
SELECT 
  Month,
  Yearly_Sales AS Current_Year_Sales,
  Previous_Year_Sales,
  ((Yearly_Sales - Previous_Year_Sales) / Previous_Year_Sales) * 100 AS Growth_Pct
FROM YearlySales
WHERE Previous_Year_Sales IS NOT NULL;

11.
SELECT 
  Operation_ID,
  Timestamp AS Original_Timestamp,
  CONVERT_TIMEZONE('UTC', Timestamp) AS UTC_Timestamp
FROM Warehouse_Ops;

12.
SELECT 
  EXTRACT(HOUR FROM Timestamp) AS Hour_Of_Day,
  COUNT(*) AS Transaction_Count
FROM Sales_Transactions
GROUP BY EXTRACT(HOUR FROM Timestamp)
ORDER BY COUNT(*) DESC
LIMIT 1;

13.
WITH CustomerIntervals AS (
  SELECT 
    Customer_ID,
    Date,
    DATEDIFF(Date, LAG(Date) OVER (PARTITION BY Customer_ID ORDER BY Date)) AS Days_Between
  FROM Sales_Transactions
)
SELECT 
  c.Customer_ID,
  AVG(ci.Days_Between) AS Avg_Days_Between_Purchases
FROM CustomerIntervals ci
JOIN Customers c ON ci.Customer_ID = c.Customer_ID
WHERE ci.Days_Between IS NOT NULL
GROUP BY c.Customer_ID;

14.
WITH ProductMonthlySales AS (
  SELECT 
    s.SKU_Code,
    EXTRACT(MONTH FROM s.Date) AS Month,
    SUM(s.Gross_Amount) AS Monthly_Sales,
    SUM(SUM(s.Gross_Amount)) OVER (PARTITION BY s.SKU_Code) AS Total_Sales
  FROM Sales_Transactions s
  GROUP BY s.SKU_Code, EXTRACT(MONTH FROM s.Date)
),
SeasonalProducts AS (
  SELECT 
    SKU_Code,
    STRING_AGG(Month, ', ' ORDER BY Month) AS Seasonal_Months,
    SUM(Monthly_Sales) / MAX(Total_Sales) * 100 AS Pct_Total_Sales
  FROM ProductMonthlySales
  GROUP BY SKU_Code
  HAVING SUM(Monthly_Sales) / MAX(Total_Sales) >= 0.8
    AND COUNT(DISTINCT Month) = 3
    AND MAX(Month) - MIN(Month) = 2
)
SELECT * FROM SeasonalProducts;

15.
WITH RECURSIVE DateRange AS (
  SELECT CAST('2021-01-01' AS DATE) AS Date
  UNION ALL
  SELECT DATEADD(day, 1, Date)
  FROM DateRange
  WHERE Date < '2023-12-31'
)
SELECT 
  Date,
  DAYNAME(Date) AS Day_Of_Week,
  MONTHNAME(Date) AS Month,
  CONCAT('Q', QUARTER(Date)) AS Quarter,
  EXTRACT(YEAR FROM Date) AS Year,
  CASE WHEN DAYOFWEEK(Date) IN (1,7) THEN 1 ELSE 0 END AS Is_Weekend
FROM DateRange;