SQL Server nullif, isnull, isnumeric, cast function example

If (object_id ('t_ test')> 0)
Drop table t_test
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Create Table t_test (A SQL _variant, B SQL _variant, C SQL _variant)
Insert into t_test select 1, 1, 'A'
Insert into t_test select 1, getdate (), null
Insert into t_test select 'A', null, 1
Insert into t_test select 3, null, null
Insert into t_test select null, null, null
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Select * From t_test
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Select
Count (*) -- total
, Count (nullif (1, 1) -- returns 0 forever
, Count (a) -- a quantity
, Count (B) -- number of B
, Count (distinct a) -- A does not repeat the number
, Count (isnull (B, c) -- the number of B or C values not null
, Count (coalesce (a, B, c) -- the number of A, B, or C is not null.
, Count (nullif (A, B) -- A is not equal to the number of B
, Count (nullif (isnumeric (cast (A as varchar (38), 0) -- A is the number of digits.
From t_test