I have two tables like these:

Table 1

id codpr price 
1  456   6300.98
2  321    540.00
3  123   1275.90
... 

Table 2

id tb1id codpr price
1  2     321   540.00
2  2     453  1345.90
3  2     125  6570.80
... 

Table 1 contains historic transactions of codprs. Table 2 contains extended transactions associated with a single movement (for example: trans id 2 is a extended one).
When there is a multi-transaction, Table 2 contains all codprs, including the Table 1 codpr.

So the result needs to reflect lines from Table 1 only when there is no related lines in Table 2. When Table 2 contains related records, The result should yield only the lines in Table 2.

The result of the example would look like this :

cid codpr price 
1   456   6300.98

2   321    540.00
2   453   1345.90
2   125   6570.80

3   123   1275.90

... 

(cid is not necessary. It appears only for control). 

I know how join two tables and select rows with matching in another table but I don’t know how discriminate the output.