How Can I Pivot a Table Without Using Aggregate Functions?

Pivot table data conversion without aggregate functions

In the field of data processing, sometimes it is necessary to reshape data into a format that is more user-friendly or more convenient for analysis. One of the most common techniques for achieving this is pivoting, where data is transformed into a wider layout. Although pivoting usually involves aggregated values, it can also be performed without using any aggregate functions.

Consider the following table:

<code class="language-sql">CREATE TABLE Data (
  CustomerID int,
  DBColumnName varchar(50),
  Data varchar(50)
);

INSERT INTO Data (CustomerID, DBColumnName, Data)
VALUES
  (1, 'FirstName', 'Joe'),
  (1, 'MiddleName', 'S'),
  (1, 'LastName', 'Smith'),
  (1, 'Date', '12/12/2009'),
  (2, 'FirstName', 'Sam'),
  (2, 'MiddleName', 'S'),
  (2, 'LastName', 'Freddrick'),
  (2, 'Date', '1/12/2009'),
  (3, 'FirstName', 'Jaime'),
  (3, 'MiddleName', 'S'),
  (3, 'LastName', 'Carol'),
  (3, 'Date', '12/1/2009');</code>

This table contains data for multiple customers, where each record represents a specific attribute (FirstName, MiddleName, LastName, Date) and its associated value. The goal is to pivot this data into a more readable format:

<code class="language-sql">CREATE TABLE PivotedData (
  CustomerID int,
  FirstName varchar(50),
  MiddleName varchar(50),
  LastName varchar(50),
  Date varchar(50)
);

INSERT INTO PivotedData (CustomerID, FirstName, MiddleName, LastName, Date)
VALUES
  (1, 'Joe', 'S', 'Smith', '12/12/2009'),
  (2, 'Sam', 'S', 'Freddrick', '1/12/2009'),
  (3, 'Jaime', 'S', 'Carol', '12/1/2009');</code>

It is important to note that this transformation does not aggregate the data. Instead, it retains a unique value for each attribute for each customer.

To achieve this transformation without using aggregate functions, we can use a CASE expression in a grouped SELECT statement:

<code class="language-sql">SELECT
  CustomerID,
  MIN(CASE DBColumnName WHEN 'FirstName' THEN Data END) AS FirstName,
  MIN(CASE DBColumnName WHEN 'MiddleName' THEN Data END) AS MiddleName,
  MIN(CASE DBColumnName WHEN 'LastName' THEN Data END) AS LastName,
  MIN(CASE DBColumnName WHEN 'Date' THEN Data END) AS Date
FROM Data
GROUP BY CustomerID;</code>

This query uses a series of CASE expressions to conditionally select the value associated with each attribute for each customer. The MIN() function is used to retrieve a single value that meets a specified condition, ensuring that we only contain one value per attribute. By grouping the results by CustomerID, we create a row for each customer with its corresponding attributes and values.

This technique allows for flexible pivoting of data without the use of aggregate functions. It is particularly useful when the data requires minimal transformation and the original values ​​need to be preserved.

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