This is exactly what I was looking for. Unfortunately it doesn't work though. It always shows the second template, the one defined in 20=COA ...

I got it to work. Found this on another site:
styles.content.get = CONTENT
styles.content.get {
table = tt_content
select.orderBy = sorting
select.where = colPos=0
select.languageField = sys_language_uid
}

styles.content.getLeft < styles.content.get
styles.content.getLeft.select.where = colPos=1

styles.content.getRight < styles.content.get
styles.content.getRight.select.where = colPos=2

styles.content.getBorder < styles.content.get
styles.content.getBorder.select.where = colPos=3

I had to add this manually to the Typoscript and then it worked.

If you also use css_styled_content (CSC) then you shouldn't need to use the second post by Igor.

Using CSC will have previously defined what each of the styles.content.get are.

If you use automaketemplate:

temp.resource = COA
temp.resource {
10 = COA
10 {
if.isTrue.numRows < styles.content.getRight
10 = TEMPLATE
10 {

template = FILE
template.file = fileadmin/tmpl/tmpl01.html
}
}
20 = COA
20 {
if.isFalse.numRows < styles.content.getRight
10 = TEMPLATE
10 {

template = FILE
template.file = fileadmin/tmpl/tmpl02.html
}
}
}

### Configuration of the auto template parser: ###
plugin.tx_automaketemplate_pi1 {
content < temp.resource

Beware of double-using the same if option. E.g. what I had was:

ifTrue.numRows < styles.content.getLeft
ifTrue.numRows < styles.content.getRight

and it ignores the first row. That's probably the expected behaviour but strange for a newbie like me.

The workaround was to use:

value = 0
ifGreaterThan.numRows < styles.content.getLeft
ifTrue.numRows < styles.content.getRight

(or .equals instead of repeated isFalse)

Please help me with such a problem

I need to load CSS file according to different conditions

(if left and normal columns are not empty)
(if right and normal columns are not empty)
(if left and right and normal columns are not empty)

is it possible to make such complex conditions using typoscript?