sqlite> SELECT c.id, c.fname, COUNT(*)
   ...> FROM customer c INNER JOIN sales_order so
   ...> WHERE c.id = so.cust_id AND c.id IN (
   ...> SELECT s.cust_id
   ...> FROM sales_order s
   ...> WHERE s.sales_rep = 129)
   ...> GROUP BY c.id, c.fname;
101|Michaels|11
103|Erin|8
104|Meghan|11
107|Kelly|11
110|Michael|10
111|Dylan|8
116|Brian|7
117|Meredith|8
119|Tomm|6
121|Pete|8
122|Al|6
126|Sam|5
127|Mary|6
128|Hardy|6
131|Daljit|5
132|Marilyn|7
136|Tommie|8
137|Polly|6
138|Regus|6
143|Peter|6
144|Fangmei|7
149|Hans|6
155|Milo|4
157|William|6
162|Melba|3
167|Nicklas|4
168|Almen|6
170|Manh|5
173|Grover|3
178|Suresh|4
179|Marsha|4
180|Edith|4
182|Leilani|7
184|Anoush|4
189|Herbert|8
190|Randy|7
191|Marta|6
194|Jen-Chang|5
197|Maio|6
198|Sheng|9
199|Ella|9
201|Amit|11
202|Bubba|8
204|Robert|11
205|Elmo|8

sqlite> SELECT c.id, c.fname, COUNT(*)
   ...> FROM customer c INNER JOIN sales_order so
   ...> ON c.id = so.cust_id
   ...> GROUP BY c.id, c.fname
   ...> HAVING so.sales_rep = 129;
121|Pete|8
127|Mary|6
131|Daljit|5
137|Polly|6
157|William|6
170|Manh|5
173|Grover|3
194|Jen-Chang|5
199|Ella|9
205|Elmo|8