Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Some day soon (5.6.4), MySQL will provide <a href="http://dev.mysql.com/doc/refman/5.6/en/fractional-seconds.html" rel="noreferrer">fractional seconds</a> in TIMESTAMP columns, however, even fractional seconds aren't guaranteed to be unique, though theoretically, they'd most often be unique, especially if you limited MySQL to a single thread.</p> <p>You can use a <a href="http://dev.mysql.com/doc/refman/5.5/en/miscellaneous-functions.html#function_uuid" rel="noreferrer">UUID</a> if you need a unique number that is ordered temporally.</p> <p><code>SELECT UUID()</code> yields something like:</p> <pre><code>45f9b8d6-8f00-11e1-8920-842b2b55ce56 </code></pre> <p>And some time later:</p> <pre><code>004b721a-8f01-11e1-8920-842b2b55ce56 </code></pre> <p>The first three portions of a UUID consist of the time, however, they're in order from highest precision to least, so you'd need to reverse the first three portions using <code>SUBSTR()</code> and <code>CONCAT()</code> like this:</p> <pre><code>SELECT CONCAT(SUBSTR(UUID(), 15, 4), '-', SUBSTR(UUID(), 10, 4), '-', SUBSTR(UUID(), 1, 8)) </code></pre> <p>Yields:</p> <pre><code>11e1-8f00-45f9b8d6 </code></pre> <p>You obviously couldn't use a function like this as a default value, so you'd have to set it in code, but it's a guaranteed unique temporally ordered value. UUID() works at a much lower level than seconds (clock cycles), so it's guaranteed unique with each call and has low overhead (no locking like auto_increment).</p> <p>Using the UUID() on the database server may be preferred to using a similar function, such as PHP's <code>microtime()</code> function on the application server because your database server is more centralized. You may have more than one application (web) server, which may generate colliding values, and microtime() still doesn't guarantee unique values.</p>
    singulars
    1. This table or related slice is empty.
    1. POCan I get a unique TIMESTAMP for every record in MySQL
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USMarcus Adams
    1. USMarcus Adams
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POCan I get a unique TIMESTAMP for every record in MySQL
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. CO+1 great info. Few questions however arised. How does the three first numbers guarantee temporal order? Manual says just vaguely: "The first three numbers are generated from a timestamp." Should the full `UUID` be always used (just the first three values reversed for ordering)? Where to find more info about this function. Manual didn't mention the "highest precision to least" order?
      singulars
      1. PO
      1. USZZ-bb
    2. CO@ZZ-bb, The MySQL manual doesn't include the details because the UUID format that they use is a [standard](http://pubs.opengroup.org/onlinepubs/9629399/toc.pdf). The fourth part of the UUID will change whenever you set the clock back. This is to ensure that the value as a whole is unique. As long as you don't mess with your clock, the first three parts are fine.
      singulars
      1. PO
      1. USMarcus Adams
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload