How to Convert Comma-Separated Columns into Multiple Rows in Db2
Many applications require data to be stored in a relational table structure, where each record represents a unique entity and its attributes. However, sometimes data may be structured differently, such as in a comma-separated format within a single column. Transforming such data into a relational structure can be challenging, but Db2 offers a solution using recursive SQL.
Let's consider an example where a table contains a column with comma-separated values:
Id | FK_ID | Reference ----------------------- 1 2100 GI2, GI32 2 2344 GI56
Our goal is to transform this data into a table with multiple rows, where each row represents a distinct reference:
Id | FK_ID | Reference ----------------------- 1 2100 GI2 2 2100 GI32 3 2344 GI56
The recursive SQL query below achieves this transformation:
WITH unpivot (lvl, id, fk_ref, reference, tail) AS ( SELECT 1, id, fk_ref, CASE WHEN LOCATE(',',reference) > 0 THEN TRIM(LEFT(reference, LOCATE(',',reference)-1)) ELSE TRIM(reference) END, CASE WHEN LOCATE(',',reference) > 0 THEN SUBSTR(reference, LOCATE(',',reference)+1) ELSE '' END FROM yourtable UNION ALL SELECT lvl + 1, id, fk_ref, CASE WHEN LOCATE(',', tail) > 0 THEN TRIM(LEFT(tail, LOCATE(',', tail)-1)) ELSE TRIM(tail) END, CASE WHEN LOCATE(',', tail) > 0 THEN SUBSTR(tail, LOCATE(',', tail)+1) ELSE '' END FROM unpivot WHERE lvl <p>This query unpivots and iteratively splits the comma-separated values into separate rows. The result is a relational table in the desired format. Note: the query has not been tested and may require minor adjustments.</p>
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