basic internal structure

internal/service/main.go

@@ -0,0 +1,16 @@
+package service
+
+import (
+	"Portifolio/internal/model"
+	"database/sql"
+
+	_ "github.com/mattn/go-sqlite3"
+)
+
+func AddCompany(input model.CompanyInput, db *sql.DB) error {
+	_, err := db.Exec(
+		`INSERT INTO companies (name, shares_outstanding, price, currency_id) VALUES (?, ?, ?, ?)`,
+		input.Name, input.SharesOutstanding, input.Price, input.CurrencyID,
+	)
+	return err
+}