Finding the Highest Total Price and Converting It

In this article, we will explore a SQL query that finds the highest total price in a database table, converts it to US dollars using an exchange rate, and returns the trade ID, stock ID, and converted price.

Background

Database tables are used to store data for various purposes. In this case, we have three tables: trade, stock_exchange, and currency. The trade table contains information about trades, including the trade ID, stock ID, transaction time, shares, and price total. The stock_exchange table stores information about stock exchanges, including the stock exchange ID, name, symbol, and currency ID. The currency table contains information about currencies, including the currency ID, name, and symbol.

The conversion process involves joining these tables to get the correct data and then applying an exchange rate to convert the price total from the local currency to US dollars.

Problem Statement

Given a query that lists trade IDs, stock IDs, and total prices converted to US dollars, we need to find the highest total price and return the corresponding trade ID, stock ID, and converted price.

SQL Query Analysis

The provided SQL query is as follows:

SELECT 
    tr.trade_id, tr.stock_id, round(tr.price_total * con.exchange_rate,2) 
    AS "US Dollars"

FROM trade tr 
JOIN stock_exchange se 
ON se.STOCK_EX_ID = tr.STOCK_EX_ID

JOIN currency curr 
ON curr.CURRENCY_ID = se.currency_id

JOIN conversion con 
ON con.from_CURRENCY_ID = curr.CURRENCY_ID

WHERE (tr.PRICE_TOTAL) = (SELECT Max(price_total) FROM trade)
    AND curr.name = 'Dollar'
    AND tr.stock_ex_id IS NOT NULL
GROUP BY tr.trade_id, tr.stock_id, round(tr.price_total), tr.price_total, 
round(tr.price_total * con.exchange_rate,2);

The query starts by joining the trade table with the stock_exchange and currency tables on their respective IDs. It then joins the conversion table to apply an exchange rate.

However, there are several issues with this query:

The WHERE clause is using a subquery to find the maximum price total, but it’s not correctly filtering the data.
The GROUP BY clause is listing all columns from the query, which is unnecessary and can lead to incorrect results.
The round(tr.price_total * con.exchange_rate,2) expression is repeated in the SELECT and GROUP BY clauses, which is unnecessary.

Solutions

To fix these issues, we need to modify the query to correctly filter the data and remove unnecessary expressions. Here are two possible solutions:

Solution 1: Filter Data Using a Subquery

We can start by running a subquery to find the maximum price total in the trade table:

SELECT 
    tr.trade_id, tr.stock_id, round(tr.price_total * con.exchange_rate,2) 
    AS "US Dollars"

FROM trade tr 
JOIN stock_exchange se 
ON se.STOCK_EX_ID = tr.STOCK_EX_ID

JOIN currency curr 
ON curr.CURRENCY_ID = se.currency_id

JOIN conversion con 
ON con.from_CURRENCY_ID = curr.CURRENCY_ID

WHERE tr.price_total = (SELECT Max(trm.price_total) FROM trade trm)
    AND curr.name = 'Dollar'
    AND tr.stock_ex_id IS NOT NULL;

This query uses a subquery to find the maximum price total in the trade table and then filters the data based on this value.

Solution 2: Use a JOIN with a LEFT JOIN

Another approach is to use a JOIN with a LEFT JOIN to filter the data:

SELECT 
    tr.trade_id, tr.stock_id, round(tr.price_total * con.exchange_rate,2) 
    AS "US Dollars"

FROM trade tr 
LEFT JOIN stock_exchange se 
ON se.STOCK_EX_ID = tr.STOCK_EX_ID

LEFT JOIN currency curr 
ON curr.CURRENCY_ID = se.currency_id
AND curr.name = 'Dollar'

LEFT JOIN conversion con 
ON con.from_CURRENCY_ID = curr.CURRENCY_ID

WHERE tr.price_total = (SELECT Max(trm.price_total) FROM trade trm)
    AND se.STOCK_EX_ID IS NOT NULL;

This query uses LEFT JOINs to join the tables and then filters the data based on the maximum price total.

Conclusion

Finding the highest total price in a database table and converting it to US dollars using an exchange rate requires careful analysis of the SQL query. By using subqueries or JOINs with LEFT JOINs, we can correctly filter the data and get the desired results.

In this article, we have explored two possible solutions for finding the highest total price and converting it to US dollars. We have also discussed the importance of carefully analyzing the SQL query and removing unnecessary expressions to avoid incorrect results.

Example Use Cases

The following example use cases demonstrate how to find the highest total price in a database table:

Finding the highest total price for a specific stock:

SELECT trade.trade_id, trade.stock_id, round(trade.price_total * conversion.exchange_rate,2) AS “US Dollars”

FROM trade JOIN stock_exchange ON stock_exchange.STOCK_EX_ID = trade.STOCK_EX_ID

WHERE trade.stock_id = ‘Stock ID’ AND (trade.price_total * conversion.exchange_rate) = (SELECT Max(price_total) FROM trade);


*   Finding the highest total price for all stocks:
    ```markdown
SELECT 
    trade.trade_id, trade.stock_id, round(trade.price_total * conversion.exchange_rate,2) 
    AS "US Dollars"

FROM trade 
JOIN stock_exchange 
ON stock_exchange.STOCK_EX_ID = trade.STOCK_EX_ID

WHERE (trade.price_total * conversion.exchange_rate) = (SELECT Max(price_total) FROM trade);

Finding the highest total price for a specific currency:

SELECT trade.trade_id, trade.stock_id, round(trade.price_total * conversion.exchange_rate,2) AS “US Dollars”

FROM trade JOIN stock_exchange ON stock_exchange.STOCK_EX_ID = trade.STOCK_EX_ID

WHERE (trade.price_total * conversion.exchange_rate) = (SELECT Max(price_total) FROM trade)

AND currency.name = ‘Dollar’;


Note that these examples assume that the `conversion` table contains an exchange rate for US dollars. The actual SQL query may need to be modified based on the specific requirements of your database.

Last modified on 2024-07-16