Filter by date using SQL

问题

I would like to know what do you think:

I have to get all the connections I had to the system during a session. To automatize this process, I decided to use current_date%, which won't work because current_date is not a string, it's a function.

So my question is if anyone can help me with the query to get the number of all the connections of the current day.

Thanks in advance!

My shitty code:

SELECT COUNT(id) FROM user_connections
WHERE connectiondate LIKE 'CURRENT_DATE%'

回答1:

The best way (from a performance perspective) is to use logic like this:

WHERE connectiondate >= CURRENT_DATE AND
      connectiondate < CURRENT_DATE + INTERVAL '1 DAY'

Not all databases support ISO/ANSI standard syntax for dates, so the exact expression in your database may differ.

回答2:

You only need connectiondate >= CURRENT_DATE:

SELECT COUNT(id) FROM user_connections
WHERE connectiondate >= CURRENT_DATE

if the data type of connectiondate is datetime.
If it is date then a simple connectiondate = CURRENT_DATE will do.

来源：https://stackoverflow.com/questions/55026314/filter-by-date-using-sql