PostgreSQL query the current time timestamp

First, the problem

　　Using PostgreSQL to get the current system time stamp. As we all know, in MySQL like this:

   select UNIX_TIMESTAMP(NOW())

Second, the solution

(1) to the nearest second

　　select floor(extract(epoch from now())); 结果："1574826646"

 

(2) accurate to fractions of a second

　　select extract(epoch from now());结果："1574826646.79929"

 

(3) to the millisecond:

　　select floor(extract(epoch from((current_timestamp - timestamp '1970-01-01 00:00:00')*1000)));