SQL: Calculate percentage of column

# Starting with a table.
> select * from sales;
+-------+------+
|  rep  | sale |
+-------+------+
|  Bob  |  15  |
| Sally |  30  |
| Peter |  15  |
+-------+------+
# Use a cross join.
>  SELECT Rep, Sale, Sale * 100 / t.s AS `percent of total`
.. FROM sales
.. CROSS JOIN (SELECT SUM(sale) AS s FROM sales) t;
+-------+------+------------------+
|  rep  | sale | percent of total |
+-------+------+------------------+
|  Bob  |  15  |        25        |
| Sally |  30  |        50        |
| Peter |  15  |        25        |
+-------+------+------------------+
# Or use a subselect/subquery.
>  SELECT Rep, Sale,
.. Sale * 100 / (SELECT SUM(sale) AS s FROM sales) AS `percent of total`
.. FROM sales;

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