mysql - having trouble writing a query that list all salesmen that did not sell to a particular customer -

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i successful in writing query lists salesmen did sell particular customer, not have not. suspect because same salesmen sold specific customer, sold other customers. 

  select a.name salesperson inner join orders b on    a.salesperson_id = b.salesperson_id cust_id="4";

i thinking modifying same query trick:

  .... a.salesperson_id <> b.salesperson_id cust_id="4";

but result lists salesmen. due fact same salesmen returned in original query, sold other customers

the 3 tables this: 

               salesperson table                       salesperson_id,     name,     age,      salary                           1                   abe        61       140000                          2                   bob        34        44000                          5                  chris       34        40000                          7                   dan        41        52000                          8                   ken        57       115000                          11                  joe        38        38000                      customer table                     cust_id,       name,     city           industry type                        4            faralon    sacramento            h                       6             apple       cupertino           s                       7            honda       ny                   b                       9            kolb      oshkosh                b               orders table               number,        order_date,   cust_id,  salesperson_id,   amount              10              8/2/1996           4             2         540              20             1/30/1999          4             8        1800              30             7/14/1995          9             1         460             40             1/29/1998           7             2        2400             50             2/3/1998            6              7        600             60             3/2/1998            6              7        720             70             5/6/1998            9              7        150

any appreciated. ~alpinehyker

you can this:

select a.name salesperson  left join orders b on a.salesperson_id = b.salesperson_id , b.cust_id="4" b.number null

so, salepersons, left join orders customer 4, , return rows there no such order.

i assuming number primary key orders, or @ least not null.


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