Can I compare MysQL timestamp with datetime columns? is it bad? -

so, have table columns "abc" timestamp , "bcd" datetime.

if this:

select * mytable abc > bcd 

is bad? , affect performance?

how compare in terms of performance?

yes, can compare datetime timestamp. it's not bad, aware of following:

remember although datetime, date, , timestamp values can specified using same set of formats, types not have same range of values. example, timestamp values cannot earlier 1970 utc or later '2038-01-19 03:14:07' utc.

this means date such '1968-01-01', while legal datetime or date value, not valid timestamp value , converted 0.

from mysql reference manual :: datetime, date, , timestamp types.

note how following test cases works fine:

create table t1 (d1 datetime, d2 timestamp);  insert t1 values ('1968-01-01 00:00:00', '1980-01-01 00:00:00'); insert t1 values ('2040-01-01 00:00:00', '1980-01-01 00:00:00');  select * t1 d2 < d1; +---------------------+---------------------+ | d1                  | d2                  | +---------------------+---------------------+ | 2040-01-01 00:00:00 | 1980-01-01 00:00:00 | +---------------------+---------------------+ 1 row in set (0.00 sec)  select * t1 d2 > d1; +---------------------+---------------------+ | d1                  | d2                  | +---------------------+---------------------+ | 1968-01-01 00:00:00 | 1980-01-01 00:00:00 | +---------------------+---------------------+ 1 row in set (0.00 sec)  select * t1 d2 < '2040-01-01 00:00:00'; +---------------------+---------------------+ | d1                  | d2                  | +---------------------+---------------------+ | 1968-01-01 00:00:00 | 1980-01-01 00:00:00 | | 2040-01-01 00:00:00 | 1980-01-01 00:00:00 | +---------------------+---------------------+ 2 rows in set (0.00 sec)  select * t1 d2 > '2040-01-01 00:00:00'; empty set (0.00 sec)