Kapil, Cross join means Cartesian product. When query have multiple joins, it solve it from left to right. So first cross join take place between table #T1 and #T2. It gives 2 (1 *2) rows. Now these 2 rows have cross join with #T3. It gives 6 (2*3) rows. Output of this query look like below.

id1id2id3

111

112

113

121

122

123

Now calculate sum of column id3. its 1+2+3+1+2+3 = 12.

So Total row count is 6 and total of id3 column is 12.

I think this help you. 🙂