How Can I Easily Split Comma-Separated Values in SQLite Using Common Table Expressions?

Creating an Easy Approach to Split Comma-Separated Values in SQLite

Introduction

Extracting individual values from comma-separated strings is a common requirement in data analysis. In SQLite, there's no straightforward equivalent to SQL's SubString() function, making this task somewhat challenging. However, with the help of Common Table Expressions (CTEs), we can create an efficient and intuitive solution.

The Solution: Using a CTE

A CTE allows us to define and name a temporary result set. By leveraging recursion within a CTE, we can iteratively parse the comma-separated string, extracting each value one at a time.

The CTE declaration in our case looks something like this:

WITH split(word, csv) AS (
  -- 'initial query' (see SQLite docs linked above)
  SELECT 
    '', 
    'Auto,A,1234444'||','
  
  -- 'recursive query'
  UNION ALL SELECT
    substr(csv, 0, instr(csv, ',')), 
    substr(csv, instr(csv, ',') + 1)
  FROM split
  WHERE csv != ''
)

In the 'initial query,' we create a starting point for the recursive portion of the CTE. We specify an empty string for 'word' and append a comma-separated string with an extra comma to indicate the end of the CSV.

The 'recursive query' is where the magic happens. It uses the instr() function to find the position of the first comma in the 'csv' field. Then, it splits the 'csv' field using substr() into 'word' and the remaining 'csv' portion.

Recursion is used to continue splitting the remaining 'csv' portion until there are no more commas left, effectively extracting all the comma-separated values.

Retrieving the Split Values

Once the CTE has defined the split values, we can retrieve them using a simple query:

SELECT word FROM split 
WHERE word!='';

The WHERE clause filters out the empty strings that represent the initial and terminal values.

Output and Benefits

The output of the query is as follows:

Auto
A
1234444

This approach provides several benefits:

• It uses a recursive CTE, which is an elegant and efficient way to handle the iterative nature of splitting.
• The output is easy to understand and work with.
• It doesn't require using Replace() and Trim() functions, which can be more complex and error-prone.

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