MySQL 8.0

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CREATE TABLE A (x varchar(20));      

    INSERT INTO A
    (x )
    VALUES
         ( 'ab'),
         ( 'zx'),
         ( 'ab'),
         ( 'cb'),
         ( 'cc'),
         ( 'cc');

    SELECT * FROM A;

Records: 6  Duplicates: 0  Warnings: 0




x


ab

zx

ab

cb

cc

cc


CREATE TABLE B (x1 varchar(20), t varchar(20));

    INSERT INTO B
    (x1 , t )
    VALUES
         ( 'ab', 'tom' ),
         ( 'zx', 'banks' );

    SELECT * FROM B;

Records: 2  Duplicates: 0  Warnings: 0




x1
t


ab
tom

zx
banks


select distinct A.x from A
where A.x NOT IN (Select distinct B.x1 from B);


x


cb

cc


 with cte1 as(
   Select * 
  from A LEFT JOIN B 
  on A.x = B.x1
)
   Select * from cte1;


x
x1
t


ab
ab
tom

zx
zx
banks

ab
ab
tom

cb
null
null

cc
null
null

cc
null
null


 with cte1 as(
   Select * 
  from A LEFT JOIN B 
  on A.x = B.x1
)
   Select distinct x from cte1 where t is NULL;


x


cb

cc

x	x1	t
ab	ab	tom
zx	zx	banks
ab	ab	tom
cb	null	null
cc	null	null
cc	null	null