DATE_SUB will do part of it depending on what you want

    mysql&gt; SELECT DATE_SUB(NOW(), INTERVAL 30 day);
    2009-06-07 21:55:09

    mysql&gt; SELECT TIMESTAMP(DATE_SUB(NOW(), INTERVAL 30 day));
    2009-06-07 21:55:09

    mysql&gt; SELECT UNIX_TIMESTAMP(DATE_SUB(NOW(), INTERVAL 30 day));
    1244433347

You could use:

    SELECT unix_timestamp(now()) - unix_timestamp(maketime(_,_,_));

For unix timestamps or:

    SELECT addtime(now(),maketime(_,_,_));

For the standard MySQL date format.

If you need negative hours from timestamp

    mysql&gt;SELECT now( ) , FROM_UNIXTIME( 1364814799 ) , HOUR( TIMEDIFF( now( ) , FROM_UNIXTIME( 1364814799 ) ) ) , TIMESTAMPDIFF( HOUR , now( ) , FROM_UNIXTIME( 1364814799 ) ) 
    2013-06-19 22:44:15 	2013-04-01 14:13:19 	1904 	-1904

this
    
    TIMESTAMPDIFF( HOUR , now( ) , FROM_UNIXTIME( 1364814799 ) ) 
will return negative and positive values, if you need to use x&gt;this_timestamp

but this

    HOUR( TIMEDIFF( now() , FROM_UNIXTIME( 1364814799 ) ) )
will return only positive, hours

I&#39;m using OleDb to read from an excel workbook with many sheets. 

I need to read the sheet names, but I need them in the order they are defined in the spreadsheet; so If I have a file that looks like this;


    |_____|_____|____|____|____|____|____|____|____|
    |_____|_____|____|____|____|____|____|____|____|
    |_____|_____|____|____|____|____|____|____|____|
    \__GERMANY__/\__UK__/\__IRELAND__/
    
Then I need to get the dictionary

    1=&quot;GERMANY&quot;, 
    2=&quot;UK&quot;, 
    3=&quot;IRELAND&quot;

I&#39;ve tried using `OleDbConnection.GetOleDbSchemaTable()`, and that gives me the list of names, but it alphabetically sorts them. The alpha-sort means I don&#39;t know which sheet number a particular name corresponds to. So I get;

    GERMANY, IRELAND, UK
    
which has changed the order of `UK` and `IRELAND`. 

The reason I need it to be sorted is that I have to let the user choose a range of data by name or index; they can ask for &#39;all the data from GERMANY to IRELAND&#39; or &#39;data from sheet 1 to sheet 3&#39;.

Any ideas would be greatly appreciated.

if I could use the office interop classes, this would be straightforward. Unfortunately, I can&#39;t because the interop classes don&#39;t work reliably in non-interactive environments such as windows services and ASP.NET sites, so I needed to use OLEDB.

Using Excel OleDb to get sheet names IN SHEET ORDER

I want to write a function which can validate a given value (passed as a string) against possible values of an `enum`. In the case of a match, it should return the enum instance; otherwise, it should return a default value.

The function may not internally use `try`/`catch`, which excludes using `Enum.Parse`, which throws an exception when given an invalid argument.

I&#39;d like to use something along the lines of a `TryParse` function to implement this:

    public static TEnum ToEnum&lt;TEnum&gt;(this string strEnumValue, TEnum defaultValue)
    {
       object enumValue;
       if (!TryParse (typeof (TEnum), strEnumValue, out enumValue))
       {
           return defaultValue;
       }
       return (TEnum) enumValue;
    }


How to TryParse for Enum value?

In MySQL, how would I get a timestamp from, say 30 days ago?

Something like:

    select now() - 30

The result should return a timestamp.

MySQL get the date n days ago as a timestamp

In MySQL, how would I get a timestamp from, say 30 days ago?
Something like:
<pre><code class="hljs language-csharp">select now() - 30
</code></pre>
The result should return a timestamp.

I have a column that has comma separated data:

    1,2,3
    3,2,1
    4,5,6
    5,5,5

I&#39;m trying to run a search that would query each value of the CSV string individually.

    0&lt;first&lt;5   and  1&lt;second&lt;3  and  2&lt;third&lt;4 

I get that I could return all queries and split it myself and compare it myself. I&#39;m curious if there is a way to do this so MySQL does that processing work.

Thanks!


Can MySQL split a column?

Is it better to use `default null` or `default &quot;&quot;` for text fields in MySQL?

Why?

Update: I know what means each of them. I am interested what is better to use considering disk space and performance.

Update 2: Hey ppl! The question was &quot;what is better to use&quot; not &quot;what each means&quot; or &quot;how to check them&quot;...

MySQL: NULL vs &quot;&quot;

I store various user details in my MySQL database. Originally it was set up in various tables meaning data is linked with UserIds and outputting via sometimes complicated calls to display and manipulate the data as required. Setting up a new system, it almost makes sense to combine all of these tables into one big table of related content.

- Is this going to be a help or hindrance?
- Speed considerations in calling, updating or searching/manipulating?

Here&#39;s an example of some of my table structure(s):

- users - UserId, username, email, encrypted password, registration date, ip
- user_details - cookie data, name, address, contact details, affiliation, demographic data
- user_activity - contributions, last online, last viewing
- user_settings - profile display settings
- user_interests - advertising targetable variables
- user_levels - access rights
- user_stats - hits, tallies

---
**Edit:** I&#39;ve upvoted all answers so far, they all have elements that essentially answer my question.

Most of the tables have a 1:1 relationship which was the main reason for denormalising them.

Are there going to be issues if the table spans across 100+ columns when a large portion of these cells are likely to remain empty?

Which is more efficient: Multiple MySQL tables or one large table?

My current query looks like this:

    SELECT * FROM fiberbox f WHERE f.fiberBox LIKE &#39;%1740 %&#39; OR f.fiberBox LIKE &#39;%1938 %&#39; OR f.fiberBox LIKE &#39;%1940 %&#39;

I did some looking around and can&#39;t find anything similar to a LIKE IN() - I envision it working like this:

    SELECT * FROM fiberbox f WHERE f.fiberbox LIKE IN(&#39;%140 %&#39;, &#39;%1938 %&#39;, &#39;%1940 %&#39;)

Any ideas? Am I just thinking of the problem the wrong way - some obscure command I&#39;ve never seen.

MySQL 5.0.77-community-log

MySQL LIKE IN()?

I&#39;m using the MySQL command-line utility and can navigate through a database. Now I need to see a list of user accounts. How can I do this?

I&#39;m using MySQL version 5.4.1.


Content Type	Original Author	Original Content on Stackoverflow
Question	Ben Noland	View Question on Stackoverflow
Solution 1 - Mysql	Justin Giboney	View Answer on Stackoverflow
Solution 2 - Mysql	hundredwatt	View Answer on Stackoverflow
Solution 3 - Mysql	Petre Sosa	View Answer on Stackoverflow

MySQL get the date n days ago as a timestamp

Mysql Problem Overview

Mysql Solutions

Solution 1 - Mysql

Solution 2 - Mysql

Solution 3 - Mysql

How to TryParse for Enum value?

Using Excel OleDb to get sheet names IN SHEET ORDER

Attributions