MySQL: Creating Dynamic Views to Work with Query Parameters

Introduction

In recent times, the need to create dynamic views that can adapt to different query parameters has become increasingly important. In this article, we will explore how to achieve this using MySQL.

We’ll start by understanding the limitations of creating static views and then dive into a solution using a more dynamic approach.

Understanding Static Views

A view in MySQL is essentially a virtual table based on the result-set of an SQL statement. By default, you can’t pass parameters directly to a view declaration. However, this doesn’t mean that we can’t create dynamic views at all. Instead, we need to use a different approach to filter the results.

The Problem with Static Views

Let’s take a look at an example of how static views are typically created and used:

CREATE VIEW cuenta_contable_union_view_with_code_32 AS
(
SELECT
    cc.code, cc.description
FROM
    cuenta_contable cc
WHERE
    cc.code = '32'
)
UNION
(
SELECT
    cc1.code,
    cc1.description
FROM
    cuenta_contable cc1
INNER JOIN
    cuenta_contable cc2
ON
    cc1.parent_cuenta_contable = cc2.id_cuenta_contable
WHERE
    cc2.code = '32'
)
ORDER BY
    code ASC;

SELECT * FROM cuenta_contable_union_view_with_code_32;

As you can see, this view returns all rows where cc.code is equal to '32'. However, we want a more dynamic approach that allows us to pass query parameters.

Limitations of Using ? in Views

When we try to replace the hardcoded values with parameterized queries, MySQL throws an error. The problem lies in how views are parsed and executed by the database server.

CREATE VIEW cuenta_contable_union_view_with_code AS
(
SELECT
    cc.code, cc.description
FROM
    cuenta_contable cc
WHERE
    cc.code = '?
)
UNION
(
SELECT
    cc1.code,
    cc1.description
FROM
    cuenta_contable cc1
INNER JOIN
    cuenta_contable cc2
ON
    cc1.parent_cuenta_contable = cc2.id_cuenta_contable
WHERE
    cc2.code = '?'
)
ORDER BY
    code ASC;

This results in an error because MySQL doesn’t know how to replace the ? placeholder with actual values. So, what’s the alternative?

Dynamic Views Using Filtering

The solution lies in using filtering instead of parameterized queries directly within views. We’ll need to create a dynamic version of our view and then use it with query parameters.

Here’s an example:

CREATE VIEW cuenta_contable_union AS (
    SELECT cc.code, cc.description, cc.code selector_code
      FROM cuenta_contable cc
     UNION
    SELECT cc1.code, cc1.description, cc2.code selector_code
      FROM cuenta_contable cc1
      JOIN cuenta_contable cc2 
             ON cc1.parent_cuenta_contable = cc2.id_cuenta_contable
);

Then, we can use this view with query parameters to filter the results:

SELECT code, description
  FROM cuenta_contable_union
 WHERE selector_code = 32
 ORDER BY code ASC;

Or, if you want to support multiple values:

SELECT code, description
  FROM cuenta_contable_union
 WHERE selector_code IN (10, 20, 30)
 ORDER BY code ASC;

Best Practices

When creating dynamic views, make sure that the view is indeed faster than the original query. This can be achieved by using UNION ALL instead of UNION, which doesn’t remove duplicate rows.

Also, always consider performance when implementing dynamic views in your database schema.

Last modified on 2023-06-18