SQL

what is the difference between union and union all

UNION ALL:
COMBINES THE RESULT OF 2 QUERY AND
DOESN'T REMOVE DUPLICATE ROWS
AND DOESN'T SORT BY FIRST COLUMN

UNION:
COMBINES THE RESULT OF 2 QUERY AND
REMOVES DUPLICATE ROWS AND
SORTS BY FIRST COLUMN 

union vs union all in sql

UNION ALL:
COMBINES THE RESULT OF 2 QUERY AND
DOESN'T REMOVE DUPLICATE ROWS
AND DOESN'T SORT BY FIRST COLUMN

UNION:
COMBINES THE RESULT OF 2 QUERY AND
REMOVES DUPLICATE ROWS AND
SORTS BY FIRST COLUMN 

union and union all difference

UNION: only keeps unique records
UNION ALL: keeps all records, including duplicates

SELECT City FROM student  
UNION  
SELECT City FROM student2

SELECT City FROM student  
UNION ALL
SELECT City FROM student2

union and union all

select null
union all
select null