// Optimal SQL Solution using NOT EXISTS
char* sqlQuery = 
"SELECT DISTINCT p.product_id, p.product_name\n"
"FROM Product p\n"
"INNER JOIN Sales s ON p.product_id = s.product_id\n"
"WHERE s.sale_date >= '2019-01-01'\n"
"  AND s.sale_date <= '2019-03-31'\n"
"  AND NOT EXISTS (\n"
"    SELECT 1\n"
"    FROM Sales s2\n"
"    WHERE s2.product_id = p.product_id\n"
"      AND (s2.sale_date < '2019-01-01' OR s2.sale_date > '2019-03-31')\n"
"  );";

// C implementation
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct {
    int product_id;
    char product_name[100];
} Product;

typedef struct {
    int product_id;
    char sale_date[11];
} Sale;

typedef struct {
    int product_id;
    char product_name[100];
} Result;

Result* optimalSolution(Product* products, int productCount, 
                       Sale* sales, int saleCount, int* resultSize) {
    Result* result = (Result*)malloc(productCount * sizeof(Result));
    *resultSize = 0;
    
    // Check each product
    for (int i = 0; i < productCount; i++) {
        int productId = products[i].product_id;
        int hasQ1Sale = 0;
        int hasNonQ1Sale = 0;
        
        // Check all sales for this product
        for (int j = 0; j < saleCount; j++) {
            if (sales[j].product_id == productId) {
                if (strcmp(sales[j].sale_date, "2019-01-01") >= 0 && 
                    strcmp(sales[j].sale_date, "2019-03-31") <= 0) {
                    hasQ1Sale = 1;
                } else {
                    hasNonQ1Sale = 1;
                }
            }
        }
        
        // Include product if it has Q1 sales but no non-Q1 sales
        if (hasQ1Sale && !hasNonQ1Sale) {
            result[*resultSize].product_id = productId;
            strcpy(result[*resultSize].product_name, products[i].product_name);
            (*resultSize)++;
        }
    }
    
    return result;
}