How to extract a Date from an SQLDateTime object in Mathematica

Question

I am trying to do a plot of a time series with `DateListPlot`. I want to feed it a time series I obtain from an SQL database. When I retrieve the time series the list is composed of `SQLDateTime` entries that `DateListPlot` doesn't understand. `In[24]:= t=SQLExecute[conn, "select timestamp,value from timeseries order by timestamp asc"]` `Out[24]={{SQLDateTime[{2010,1,1}],12.3},{SQLDateTime[{2010,1,2}],12.51}}` Doesn't work: `In[25]:= DateListPlot[t]` `DateListPlot` requires a Date tuple and doesn't understand SQLDateTime. What can I do?

Accepted Answer

The answer:

```
In[1]:= SQLDateTime[{2001, 5, 7}][[1]]
Out[1]:= {2001,5,7}
```

Mathematica thinks of everything very similarly internally. What you see as `{1, 2, 3}` is actually `List[1,2,3]`. The Part function (denoted by `[[...]]`) works just as well on any function, not just `List`.

The quick and dirty way to apply this in your case:

```
{#[[1,1]],#[[2]]}& /@ SQLExecute[...]
```

How to extract a Date from an SQLDateTime object in Mathematica

Solution

Problem