SELECT COUNT(DISTINCT CustomerID)*1.0/COUNT(*)
FROM Sales.SalesOrderHeader
WHERE CustomerID NOT IN ( 11000, 11019, 11091, 11142, 11185, 11223, 11262,
11300, 11331, 11417, 11439, 11498, 11519, 11566,
11631, 11677, 11711, 11769, 11892, 11935, 12008,
12054, 12127, 12196, 12291, 12321, 12363, 12489,
12559, 12616, 12760, 12880, 12969, 13038, 13096,
13175, 13231, 13270, 13474, 13575, 13608, 13652,
13756, 13823, 13944, 13988, 14096, 14162, 14265,
14341, 14612, 14860, 14943, 15048, 15114, 15177,
15521, 15625, 15687, 15932, 15974, 16237, 16513,
16583, 16641, 16758, 16855, 16959, 17026, 17103,
17181, 17260, 17335, 17551, 17619, 17715, 17788,
17832, 17930, 18047, 18125, 18223, 18294, 18390,
18452, 18620, 18712, 18749, 19031, 19289, 19339,
19420, 19499, 19585, 20051, 20159, 20245, 20576,
20779, 20862, 20960, 21046, 21248, 21470, 21574,
21807, 21916, 22122, 22344, 22826, 23136, 23267,
23578, 23725, 24159, 24257, 24466, 24754, 24887,
25114, 25400, 25555, 25819, 25916, 25995, 26127,
26276, 26564, 26686, 26841, 27197, 27361, 27672,
28050, 28389, 28749, 28919, 29105, 29270, 29448,
29508, 29603, 29669, 29698, 29723, 29795, 29857,
29927, 29990, 30023, 30096, 30117, 30118 )