An aggregate function that returns a single string representing the argument value concatenated together for each row of the result set. If the optional separator string is specified, the separator is added between each pair of concatenated values.

Usage notes: concat() and concat_ws() are appropriate for concatenating the values of multiple columns within the same row, while group_concat() joins together values from different rows.

By default, returns a single string covering the whole result set. To include other columns or values in the result set, or to produce multiple concatenated strings for subsets of rows, include a GROUP BY clause in the query.

Return type: STRING