Associating Type Ids and Vehicle Types with Class Names

In this article, we’ll explore how to update columns 2 and 3 based on column 1 and then column 2. We’ll cover the basics of associative queries in SQL and provide a step-by-step guide on how to achieve this using an existing table.

Understanding the Problem

The problem at hand involves updating two columns, type_id and type, in a table based on the values in another column, class. The class column contains vehicle “classes” such as large cars, small SUVs, 2WD pickups, and more. We need to update the type_id column with corresponding numeric values (1-6) based on the class value and then use these values to determine the type for each row in the table.

Basic Associative Queries

An associative query is a type of SQL query that allows us to join data from multiple tables or columns. In this case, we’re using an associative query to map class names to their corresponding numeric type ids and then use these values to determine the vehicle type.

The general syntax for an associative query looks like this:

UPDATE table_name
SET column1 = value1,
    column2 = value2,
    ...
FROM (
    SELECT column1, column2, ...
    FROM another_table
) subquery
ON condition;

In our case, the subquery is a values table that contains the class names and their corresponding numeric type ids and vehicle types.

Associating Type Ids with Class Names

To start, we need to associate type ids with each class name. This can be done by creating a separate table that maps class names to their corresponding numeric type ids.

Here’s an example of how this table might look:

+-----------+---------+
| Class Name | Type Id |
+-----------+---------+
| Compact Cars | 1       |
| Midsize Station Wagons | 3      |
| Minivan - 2WD | 2       |
| Minivan - 4WD | 2       |
| ...        | ...     |
+-----------+---------+

This table can be used as a reference to determine the corresponding type id for each class name.

Using the Associative Query

Once we have our associative query set up, we can use it to update the type_id and type columns in our original table. The general syntax looks like this:

UPDATE mytable t
SET type_id = x.type_id,
    type = x.type
FROM (
    VALUES 
        ('Compact Cars', 1, 'sedan'),
        ('Midsize Station Wagons', 3, 'foo'),
        ('Minivan - 2WD', 2, 'pickup'),
        ('Minivan - 4WD', 2, 'pickup'),
)  x(class, type_id, type)
WHERE t.class = x.class;

This query uses a values table (x) to map class names to their corresponding numeric type ids and vehicle types. It then joins this table with the original table (t) on the class column.

Handling Large Numbers of Transcodifications

If we have a large number of transcodifications to perform, it might be simpler to store them all in a table that we can directly join with our query. This approach is often referred to as “normalized data” and can make our queries more efficient.

For example, we could create a separate table that contains all the class names and their corresponding numeric type ids and vehicle types:

+-----------+---------+--------+
| Class Name | Type Id | Vehicle Type |
+-----------+---------+--------+
| Compact Cars | 1       | sedan     |
| Midsize Station Wagons | 3      | foo       |
| Minivan - 2WD | 2       | pickup    |
| Minivan - 4WD | 2       | pickup    |
| ...        | ...     | ...       |
+-----------+---------+--------+

We can then use this table to join with our original query and perform the transcodifications.

Example Use Case

Let’s consider an example where we have a table mytable that contains the following data:

+-----------+-----------+
| Class Name | Vehicle Type |
+-----------+-----------+
| Large Car  | sedan      |
| Small SUV  | pickup     |
| ...        | ...        |
+-----------+-----------+

We want to update the type_id and type columns based on the values in the Class Name column. We can use our associative query to achieve this:

UPDATE mytable t
SET type_id = x.type_id,
    type = x.type
FROM (
    VALUES 
        ('Large Car', 1, 'sedan'),
        ('Small SUV', 2, 'pickup'),
        ('...'), ... (30 more values)
)  x(class, type_id, type)
WHERE t.class = x.class;

This query uses our associative query to map class names to their corresponding numeric type ids and vehicle types. It then joins this table with the original table on the class column.

Conclusion

In conclusion, associative queries provide a powerful way to join data from multiple tables or columns. By using these queries, we can update multiple columns based on values in another column. In this article, we covered how to use associative queries to associate type ids with class names and then use these values to determine the vehicle type for each row in the table.

We also discussed handling large numbers of transcodifications by storing them all in a separate table that can be directly joined with our query.

Last modified on 2025-03-23