MySQL 8.0

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-- View base column sizes
create table tmp as (select 19000+1000 ,020000, 20000 ,2.222) ;

-- Third column truncated in MySQL 8.0, but not MariaDB 10.2
create table tmp2 as (select 19000+1000 , 020000, 20000 ,2 ) union( select 2.222 , 2.222 , 2.222 , 2.222 )
-- OK in both as expected, but big difference in column sizes
create table tmp3 as (select 2.222 as a , 2.222 as b , 2.222 as c , 2.222 as d )union (select 19000+1000 , 020000, 20000 ,2.2  )
describe tmp;


Field
Type
Null
Key
Default
Extra


19000+1000
int(7)
NO

0


020000
int(6)
NO

0


20000
int(5)
NO

0


2.222
decimal(4,3)
NO

0.000



select * from tmp


19000+1000
020000
20000
2.222


20000
20000
20000
2.222


describe tmp2


Field
Type
Null
Key
Default
Extra


19000+1000
decimal(9,3)
NO

0.000


020000
decimal(8,3)
NO

0.000


20000
decimal(7,3)
NO

0.000


2
decimal(4,3)
NO

0.000



select * from tmp2


19000+1000
020000
20000
2


20000.000
20000.000
9999.999
2.000

2.222
2.222
2.222
2.222


describe tmp3


Field
Type
Null
Key
Default
Extra


a
decimal(9,3)
NO

0.000


b
decimal(9,3)
NO

0.000


c
decimal(8,3)
NO

0.000


d
decimal(4,3)
NO

0.000



select * from tmp3


a
b
c
d


2.222
2.222
2.222
2.222

20000.000
20000.000
20000.000
2.200

Field	Type	Null	Default
19000+1000	int(7)	NO	0
020000	int(6)	NO	0
20000	int(5)	NO	0
2.222	decimal(4,3)	NO	0.000

Field	Type	Null
19000+1000	decimal(9,3)	NO
020000	decimal(8,3)	NO
20000	decimal(7,3)	NO
2	decimal(4,3)	NO