MySQL 8.0

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CREATE TABLE x SELECT 'aaa' a, '999' b UNION ALL SELECT 'bbb', '888' UNION ALL SELECT 'ccc', '777';
show create table x;

Table
Create Table

x
CREATE TABLE `x` (
  `a` varchar(3) NOT NULL DEFAULT '',
  `b` varchar(3) NOT NULL DEFAULT ''
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

select * from x;

a
b

aaa
999

bbb
888

ccc
777

select * from x order by a<b;
select * from x order by a=b;
select * from x order by a<>b;
select * from x order by a<>b,b;

a
b

aaa
999

bbb
888

ccc
777

a
b

aaa
999

bbb
888

ccc
777

a
b

aaa
999

bbb
888

ccc
777

a
b

ccc
777

bbb
888

aaa
999