MySQL 5.7

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CREATE TABLE Test_A (skey INTEGER, OrderName VARCHAR(6));

INSERT INTO Test_A (skey, OrderName) VALUES
  ('100', 'Pen'),
  ('100', 'Cutter'),
  ('101', 'any');

SELECT * FROM Test_A;


skey
OrderName


100
Pen

100
Cutter

101
any


CREATE TABLE Test_B (skey INTEGER, OrderName VARCHAR(6), kit VARCHAR(4));

INSERT INTO Test_B (skey, OrderName, kit) VALUES
  ('100', 'Pen', 'True'),
  ('100', 'Cutter', null);
  
SELECT * FROM Test_B;  


skey
OrderName
kit


100
Pen
True

100
Cutter
null


SELECT a.* 
FROM Test_A a LEFT JOIN Test_B b
ON b.skey = a.skey AND b.OrderName = a.OrderName 
WHERE b.kit = 'True'
   OR (b.kit IS NULL AND NOT EXISTS (SELECT 1 FROM Test_B WHERE skey = a.skey AND kit = 'True'))


skey
OrderName


100
Pen

101
any


SELECT a.* 
FROM Test_A a 
WHERE EXISTS (SELECT 1 FROM Test_B b WHERE b.skey = a.skey AND b.OrderName = a.OrderName AND b.kit = 'True') 
OR NOT EXISTS (SELECT 1 FROM Test_B b WHERE b.skey = a.skey AND b.kit = 'True') 


skey
OrderName


100
Pen

101
any