Joe Celko's SQL for Smarties, 3rd Edition

21.5. The LIST() Aggregate Function

The LIST([DISTINCT] <string expression>) is part of Sybase’s SQL Anywhere (formerly WATCOM SQL). It is the only aggregate function to work on character strings. It takes a column of strings, removes the NULLs and merges them into a single result string with commas between each of the original strings. The DISTINCT option removes duplicates as well as NULLs before concatenating the strings. This function is a generalized version of concatenation, just as SUM() is a generalized version of addition.

MySQL 4.1 extended this function into the GROUP_CONCAT() function, which does the same thing but adds options for ORDER BY and SEPARATOR.

This is handy when you use SQL to write SQL queries. As one simple example, ...