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.
The above is the detailed content of How to Split Comma-Separated Rows in SQL?. For more information, please follow other related articles on the PHP Chinese website!

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