CURRENT_TIMESTAMP in milliseconds

Question

Is there any way to get milliseconds out of a timestamp in MySql or PostgreSql (or others just out of curiosity)?

SELECT CURRENT_TI         


        

Answer 1

The main misunderstanding in MySQL with timestamps is that MySQL by default both returns and stores timestamps without a fractional part.

SELECT current_timestamp()  => 2018-01-18 12:05:34

which can be converted to seconds timestamp as

SELECT UNIX_TIMESTAMP(current_timestamp()) => 1516272429

To add fractional part:

SELECT current_timestamp(3) => 2018-01-18 12:05:58.983

which can be converted to microseconds timestamp as

SELECT CAST( 1000*UNIX_TIMESTAMP(current_timestamp(3)) AS UNSIGNED INTEGER) ts => 1516272274786

There are few tricks with storing in tables. If your table was created like

    CREATE TABLE `ts_test_table` (
      `id` int(1) NOT NULL,
      `not_fractional_timestamp` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

than MySQL will NOT store fractional part within it:

    id, not_fractional_timestamp
    1,  2018-01-18 11:35:12

If you want to add fractional part into your table, you need to create your table in another way:

    CREATE TABLE `ts_test_table2` (
      `id` int(1) NOT NULL,
      `some_data` varchar(10) COLLATE utf8mb4_unicode_ci NOT NULL,
      `fractional_timestamp` timestamp(3) NULL DEFAULT CURRENT_TIMESTAMP(3) ON UPDATE CURRENT_TIMESTAMP(3),
      PRIMARY KEY (`id`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

that leads to required result:

    id, some_data, fractional_timestamp
    1,  8,         2018-01-18 11:45:40.811

current_timestamp() function is allowed to receive value up to 6, but I've found out (at least in my installed MySQL 5.7.11 version on Windows) that fraction precision 6 leads to the same constant value of 3 digits at the tail, in my case 688

    id, some_data, fractional_timestamp
    1,  2,         2018-01-18 12:01:54.167688
    2,  4,         2018-01-18 12:01:58.893688

That means that really usable timestamp precision of MySQL is platform-dependent:

• on Windows: 3
• on Linux: 6