Using query to fetch large data and display in HTML table with flask in Python

Browser will freeze when you pull that much data.

To avoid that use server-side pagination and provide queries with page number to backend.

PAGE_SIZE = 10def get_paginated_result(page):    # creating connection Object which will contain SQL Server Connection        connection = pypyodbc.connect('Driver={SQL Server}; Server=Server; Database=DB; UID=UserID; PWD= {Password};')  # Creating Cursor        cursor = connection.cursor()        order_by = 'id'  # should always be validated (if you get from args)    offset = (page - 1) * PAGE_SIZE    cursor.execute(        "select A, B, C, D from TABLE ORDER BY %s OFFSET %d ROWS FETCH NEXT %d ROWS ONLY"        % (order_by, offset, PAGE_SIZE)    )        Result=cursor.fetchall()    return result@app.route('/index', methods=['GET', 'POST'])def view_index():    page = abs(int(request.args.get('page')))    Result = get_paginated_result(page)    return render_template('index.html', Result=Result)@app.route('/ajax_table', methods=['GET'])def ajax_table():    page = abs(int(request.args.get('page')))    Result = get_paginated_result(page)    return render_template('ajax_table.html', Result=Result)

After that you'll need to extract table to separate HTML file ajax_table.html. So you'll have main page and table that can be paginated. For pagination recommend to use Bootstrap Pagination and add JS code to load from /ajax_table and replace table content with another page.