public static StringExpression groupConcat(Expression<String> expr, String separator) {
        return Expressions.stringOperation(SQLOps.GROUP_CONCAT2, expr, Expressions.constant(separator));
    }
Get a group_concat(expr, separator) expression

@param expr expression to be aggregated
@param separator separator string
@return group_concat(expr, separator)
querydsl-sql/src/main/java/com/querydsl/sql/SQLExpressions.java