ROW_NUMBER window function
Assigns an ordinal number of the current row within a group of rows, counting from 1, based on the ORDER BY expression in the OVER clause. If the optional PARTITION BY clause is present, the ordinal numbers are reset for each group of rows. Rows with equal values for the ORDER BY expressions receive the different row numbers nondeterministically.
Syntax
ROW_NUMBER() OVER( [ PARTITION BY expr_list ] [ ORDER BY order_list ] )
Arguments
 ( )

The function takes no arguments, but the empty parentheses are required.
 OVER

The window function clause for the ROW_NUMBER function.
 PARTITION BY expr_list

Optional. One or more column expressions that divide the results into sets of rows.
 ORDER BY order_list

Optional. One or more column expressions that defines the order of rows within a set. If no PARTITION BY is specified, ORDER BY uses the entire table.
If ORDER BY does not produce a unique ordering or is omitted, the order of the rows is nondeterministic. For more information, see Unique ordering of data for window functions.
Return type
BIGINT
Examples
The following examples use the WINSALES
table. For a description of the WINSALES
table, see Sample table for window function examples.
The following example orders the table by QTY (in ascending order), then assigns a row number to each row. The results are sorted after the window function results are applied.
SELECT salesid, sellerid, qty, ROW_NUMBER() OVER( ORDER BY qty ASC) AS row FROM winsales ORDER BY 4,1;
salesid sellerid qty row +++ 30001  3  10  1 10001  1  10  2 10006  1  10  3 40005  4  10  4 30003  3  15  5 20001  2  20  6 20002  2  20  7 30004  3  20  8 10005  1  30  9 30007  3  30  10 40001  4  40  11
The following example partitions the table by SELLERID and orders each partition by QTY (in ascending order), then assigns a row number to each row. The results are sorted after the window function results are applied.
SELECT salesid, sellerid, qty, ROW_NUMBER() OVER( PARTITION BY sellerid ORDER BY qty ASC) AS row_by_seller FROM winsales ORDER BY 2,4;
salesid  sellerid  qty  row_by_seller +++ 10001  1  10  1 10006  1  10  2 10005  1  30  3 20001  2  20  1 20002  2  20  2 30001  3  10  1 30003  3  15  2 30004  3  20  3 30007  3  30  4 40005  4  10  1 40001  4  40  2
The following example shows the results when not using the optional clauses.
SELECT salesid, sellerid, qty, ROW_NUMBER() OVER() AS row FROM winsales ORDER BY 4,1;
salesid sellerid qty row +++ 30001  3  10  1 10001  1  10  2 10005  1  30  3 40001  4  40  4 10006  1  10  5 20001  2  20  6 40005  4  10  7 20002  2  20  8 30003  3  15  9 30004  3  20  10 30007  3  30  11