how to add condition in group group_concat in mysql code example

Example 1: group_concat mysql

GROUP_CONCAT(expr);

Example 2: mysql group concat

/* By deafult separe itens by "," */
group_concat(p.nameItem) as listProdItem
/* Used <br> to list itens one below the other in HTML page */
group_concat(p.nameItem separator '<br>') as listProdItem