I have a column set (let's say column A and column B). 
Each column can have multiple points (datetime and value).
Each column set have predefined timestep. For below example it's: 600sec.

**columnA**

```
dateTime - '2013-10-05 00:10:00' 
Value - 0.51231
dateTime - '2013-10-05 00:20:00' 
Value - 0.54123
dateTime - '2013-10-05 00:30:00' 
Value - 0.53312
...
dateTime - '2013-11-14 13:30:00' 
Value - 0.53312

etc.

```

**columnB**

```
dateTime - '2013-10-05 00:10:00' 
Value - 0.51231
dateTime - '2013-10-05 00:20:00' 
Value - 0.54123
dateTime - '2013-10-05 00:50:00' 
Value - 0.54123
...
dateTime - '2013-11-14 13:20:00' 
    Value - 0.53312
dateTime - '2013-11-14 13:30:00' 
Value - 0.53312
dateTime - '2013-11-14 13:40:00' 
Value - 0.53312

```

I need to find missing data points for each column and insert NULL points so all columns would have exact amount of points.

For above examples missing data points are:

```
columnA - 2013-11-14 13:40:00
columnB - 2013-10-05 00:30:00, 2013-10-05 00:40:00

```

I know I can iterate using T-SQL or PHP (client side) for each column for given column set and check each point, but it would be very slow I think. Especially PHP solution.

There is possibly smart SQL that would be able to select missing dateTimes (gaps).

Any ideas?

UPDATE:
Because it's not clear about the DB structure.
Column is a field within the table, so, let's have a table: tblValues.
There are 3 fields: columnName, datetime and value.
In our examples columnName would be the columnA or columnB.