How to Split Comma-Separated Rows in SQL?

Split comma separated rows in SQL

In SQL, you may encounter scenarios where you need to split a column containing comma-separated values ​​into individual rows. This can be achieved through a variety of techniques, including pure SQL queries or external tools.

An efficient way to split comma separated rows in pure SQL is to use a combination of the SUBSTRING_INDEX() and CROSS JOIN functions. SUBSTRING_INDEX() Function extracts a substring from a given string based on the specified delimiter and position. CROSS JOIN Function multiplies multiple rows from different tables, creating a Cartesian product.

Using these functions, you can generate a sequence of numbers and iterate over it. For each number, you can use the SUBSTRING_INDEX() function to extract the desired comma separated values ​​from the source column. Here is a sample query:

SELECT SUBSTRING_INDEX(SUBSTRING_INDEX(t.values, ',', n.n), ',', -1) value
FROM table1 t CROSS JOIN 
(
   SELECT a.N + b.N * 10 + 1 n
     FROM 
    (SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
   ,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
    ORDER BY n
) n
WHERE n.n <= LENGTH(t.values) - LENGTH(REPLACE(t.values, ',', '')) + 1;

This query creates a sequence of numbers from 1 to 100 and iterates over it to extract comma separated values ​​from each source row. The SUBSTRING_INDEX() function is used to extract the desired value based on the position of the number in the sequence. The WHERE clause ensures that only existing comma-separated values ​​are extracted, avoiding out-of-bounds errors.

Alternatively, you can use a persistent count table to generate numeric sequences and simplify queries. The resulting query will be similar to the query above, but the subquery will be replaced by a reference to the count table.

Together, these techniques allow you to split comma-separated rows in SQL without the need for complex queries or external tools. The choice of method depends on the specific requirements of the application and performance considerations.

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