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Overview

The UNIX_MILLIS() function returns a given timestamp to a UNIX timestamp in milliseconds from 1970-01-01 00:00:00-00 (can be negative). Its syntax is illustrated below: 
SELECT UNIX_MILLIS(TIMESTAMP)
Its input type is a TIMESTAMP expression, and the return data type is BIGINT representing time in milliseconds.

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Examples

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Case #1: Basic UNIX_MILLIS() function

The below example uses the UNIX_MILLIS() function to convert a given timestamp into a UNIX timestamp in milliseconds: 
SELECT UNIX_MILLIS(TIMESTAMP "1996-5-02 7:15:00+00") AS unix_millisvalues;
The final output will be as follows: 
+-----------------------------+
| unix_millisvalues           |
+-----------------------------+
| 831021300000.000000         |
+-----------------------------+

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Case #2: UNIX_MILLIS() function using columns

Let’s suppose we have a table named time_example with the following timestamp values in the time_stamp column: 
CREATE TABLE time_example (
  time_stamp timestamp
);

INSERT INTO time_example VALUES 
('2004-07-23 11:30:00+00'),
('2011-02-12 04:45:00+00'),
('1975-08-03 07:50:00+00');

SELECT * FROM time_example;
The above query will show the following table: 
+-------------------------+
| time_example            | 
+-------------------------+
| 2004-07-23 11:30:00     |
| 2011-02-12 04:45:00     |
| 1975-08-03 07:50:00     |
+-------------------------+
We want to convert all timestamp values into UNIX timestamp values in milliseconds. To do that, we have to run the following query: 
SELECT time_stamp, UNIX_MILLIS(time_stamp) AS time_millis FROM time_example;
The output displays all the timestamp entries of the table in the **time_stamp **column and the converted UNIX milliseconds timestamp entries in the column time_millis. 
+-------------------------+-----------------------+
| time_stamp              | time_millis           |
+-------------------------+-----------------------+
| 2004-07-23 11:30:00     | 1090582200000.000000  |
| 2011-02-12 04:45:00     | 1297485900000.000000  |
| 1975-08-03 07:50:00     | 176284200000.000000   |
+-------------------------+-----------------------+