How under number of week in year to define date of day

[wer25]

How under number of week in one year to define(determine) date of Monday of this week?
Number of week I define(determine) so: to_char (dat, 'ww')
Thank

 

[sem]

You do not need to calculate the week number.
trunc(dat, 'D') will return the first day of dat week (according to your nls-settings). If your week starts on Sunday, just add 1 to the result, if on Monday - leave it untouched.