How Can I Count Items in a Comma-Separated List in MySQL?

Counting Items in a Comma-Separated List in MySQL

Determining the number of items within a comma-separated list stored in a MySQL column can be a common task in data analysis.

Using String Length Manipulation

To achieve this without using additional functions, you can exploit the difference between the original list string and its comma-stripped counterpart:

LENGTH(fooCommaDelimColumn) - LENGTH(REPLACE(fooCommaDelimColumn, ',', ''))

This expression subtracts the length of the comma-stripped string from the original string length. Since commas contribute to the overall length, their absence indicates the number of items.

Trailing Comma Handling

Note that in this case, the provided data includes an additional trailing comma. This is particularly relevant because traditional string length calculations include this trailing comma, resulting in an incorrect count. By excluding it using the REPLACE function, the accurate count is obtained.

General Case with No Trailing Comma

In general cases where the comma-separated string does not have a trailing comma, such as "foo,bar,baz," a modified expression is necessary:

LENGTH(col) - LENGTH(REPLACE(col, ',', '')) + 1

The additional 1 accounts for the missing trailing comma, ensuring a correct item count.

By employing these string manipulation techniques, you can efficiently count the items within a comma-separated list using pure SQL queries.

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