PostgreSQL - CURRENT_TIME Function

In PostgreSQL, the CURRENT_TIME function returns the current time, including the time zone. It's formatted as 'HH:MM:SS' or 'HH:MM:SS.US' (with microseconds) depending on the context, and it includes the time zone information by default.

Here's how you can use CURRENT_TIME:

1. To get the current time with time zone:

SELECT CURRENT_TIME;

2. Using it in a WHERE clause:

Imagine you have a table log_entries with a time column entry_time. If you want to fetch all logs after 3:00 PM today, you might use:

SELECT * 
FROM log_entries 
WHERE entry_time > CAST(CURRENT_DATE AS TIMESTAMP) + INTERVAL '15 hour';

(Note: This example assumes entry_time is a timestamp, so we cast the CURRENT_DATE to a timestamp and then add the hours to it.)

3. Using it in combination with interval:

To get the time 2 hours 30 minutes ago:

SELECT CURRENT_TIME - INTERVAL '2 hours 30 minutes';

Or to get the time 45 minutes from now:

SELECT CURRENT_TIME + INTERVAL '45 minutes';

Remember, CURRENT_TIME returns just the time with the time zone. If you only want the time without the time zone, you can use LOCALTIME. And if you need the current timestamp (including both date and time), you'd use CURRENT_TIMESTAMP or now().

Retrieving the current time with CURRENT_TIME in PostgreSQL:
- Description: Retrieves the current time.
- Code:
```
SELECT CURRENT_TIME;
```
Using CURRENT_TIME in WHERE clauses in PostgreSQL:
- Description: Filters records based on the current time.
- Code:
```
SELECT *
FROM your_table
WHERE time_column = CURRENT_TIME;
```
Formatting time with CURRENT_TIME in PostgreSQL:
- Description: Formats the current time as a string.
- Code:
```
SELECT TO_CHAR(CURRENT_TIME, 'HH24:MI:SS');
```
Performing time arithmetic with CURRENT_TIME in PostgreSQL:
- Description: Performs calculations involving the current time.
- Code:
```
SELECT CURRENT_TIME + INTERVAL '1 hour';
```
Handling time zones with CURRENT_TIME in PostgreSQL:
- Description: Considers time zones in time operations.
- Code:
```
SET TIME ZONE 'UTC';
SELECT CURRENT_TIME AT TIME ZONE 'America/New_York';
```
Combining CURRENT_TIME with other time functions in PostgreSQL:
- Description: Utilizes other time functions in conjunction with the current time.
- Code:
```
SELECT CURRENT_TIME, EXTRACT(HOUR FROM CURRENT_TIME), AGE(CURRENT_TIME, '12:00:00'::TIME);
```

Extracting components (hour, minute, second) with CURRENT_TIME in PostgreSQL:

Description: Extracts specific components from the current time.

Code:

SELECT EXTRACT(HOUR FROM CURRENT_TIME) AS hour,
       EXTRACT(MINUTE FROM CURRENT_TIME) AS minute,
       EXTRACT(SECOND FROM CURRENT_TIME) AS second;

Using CURRENT_TIME in INSERT and UPDATE statements in PostgreSQL:

Description: Inserts or updates records with the current time.

Code:

INSERT INTO your_table (column1, time_column) VALUES ('value', CURRENT_TIME);

UPDATE your_table SET time_column = CURRENT_TIME WHERE condition;