Awk - Print first occurrence of a set

Input file 'order-pref.txt' contains two sql UPDATE commands for each item.

$ cat order-pref.txt
computer networking book
UPDATE orders SET quantity = '5' WHERE id = '9';
UPDATE orders SET quantity = '5' WHERE id = '8';
puzzle and skill games
UPDATE orders SET quantity = '5' WHERE id = '99';
UPDATE orders SET quantity = '5' WHERE id = '98';
arithmetic sequence
UPDATE orders SET quantity = '5' WHERE id = '55';
UPDATE orders SET quantity = '5' WHERE id = '56';

Required:
For each item find and print the first UPDATE sql command (i.e. first occurrence of each set of sql commands for each item).

i.e. required output:

UPDATE orders SET quantity = '5' WHERE id = '9';
UPDATE orders SET quantity = '5' WHERE id = '99';
UPDATE orders SET quantity = '5' WHERE id = '55';

Awk solution:

$ awk '/^UPDATE/{++c;if(c%2==1)print}' order-pref.txt > o.sql

Output:

$ cat o.sql
UPDATE orders SET quantity = '5' WHERE id = '9';
UPDATE orders SET quantity = '5' WHERE id = '99';
UPDATE orders SET quantity = '5' WHERE id = '55';

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