How can I populate a user defined table quickly? - sql-server

Question

I'm trying to create a generic histogram function to obtain histogram data for an arbitrary table in my db.
My db has many tables, each one is roughly a few gigs in size. Only some of the columns are numeric.
I started off by trying to pass in a user defined table valued parameter. The signature for my user defined function looked something like this:
CREATE TYPE dbo.numArray AS TABLE (
number real NOT NULL
);
CREATE FUNCTION dbo.fn_numericHistogram (
#values dbo.numArray READONLY,
#numOfBreaks int = 10,
#rangeMin float = NULL,
#rangeMax float = NULL
)
That worked, but it did not meet my performance requirements because I had to insert the existing numeric column into my user defined table first. That takes a long time. This long-running insertion happened inside the calling stored procedure, and looks something like this:
DECLARE #TVP AS dbo.numArray;
-- Takes far too long
INSERT INTO #TVP (number)
SELECT myNumericColumn
FROM dbo.SomeLargeTable;
EXEC dbo.fn_numericHistogram #values = #TVP READONLY
To get around this, my next approach was to simply pass in the table name as an nvarchar but it involves a lot of string manipulation and is quite ugly.
Does that seem like a reasonable workaround? I'd much rather go with the first approach but I don't know if it's possible to populate a UDT "by reference".
Thanks
*Edit:
Assuming I can quickly populate the #values UDT with ~2gigs worth of numeric data. My function would look like this:
CREATE TYPE dbo.numArray AS TABLE (
number real NOT NULL
);
CREATE FUNCTION dbo.fn_numericHistogram (
#values dbo.numArray READONLY,
#numOfBreaks int = 10,
#rangeMin float = NULL,
#rangeMax float = NULL
)
RETURNS #output TABLE (
lowerBound float NOT NULL,
upperBound float NOT NULL,
[count] int NOT NULL
)
BEGIN;
DECLARE #intervalSize float;
IF (#rangeMin IS NULL AND #rangeMax IS NULL)
BEGIN
SELECT
#rangeMinOUT = MIN(number),
#rangeMaxOUT = MAX(number)
FROM #values;
END
SET #intervalSize = (#rangeMax - #rangeMin)/#numOfBreaks;
INSERT INTO #output (lowerBound, upperBound, [count])
SELECT #rangeMin+#intervalSize*FLOOR(number/#intervalSize) AS lowerBound,
#rangeMin+#intervalSize*FLOOR(number/#intervalSize)+#intervalSize AS upperBound,
COUNT(*) AS [count]
FROM (
-- Special Case the max values.
SELECT ISNULL(NULLIF(number, #rangeMax), #rangeMax - 0.5 * #intervalSize - #rangeMin AS number
FROM #values
) AS B
GROUP BY FLOOR(number/#intervalSize);
';
RETURN;
END;
GO
Otherwise, I'll have to pass in a table name, and the function bloats to something like this: (By the way, I'm not even sure if this would work as a function...perhaps I would need a stored procedure instead).
CREATE FUNCTION dbo.fn_numericHistogram (
#tableName nvarchar(200),
#numericColumnName nvarchar(200),
#numOfBreaks int = 10,
#rangeMin float = NULL,
#rangeMax float = NULL
)
RETURNS #output TABLE (
lowerBound float NOT NULL,
upperBound float NOT NULL,
[count] int NOT NULL
)
BEGIN;
DECLARE #intervalSize float;
IF (#rangeMin IS NULL AND #rangeMax IS NULL)
BEGIN
DECLARE #SQLQuery nvarchar(MAX);
SET #SQLQuery = N'
SELECT
#rangeMinOUT = CONVERT(float, MIN('+#numericColumnName+')),
#rangeMaxOUT = CONVERT(float, MAX('+#numericColumnName+'))
FROM '+#tableName+';
EXEC sp_executesql #SQLQuery, N'rangeMinOUT nvarchar(50) OUTPUT, rangeMaxOUT nvarchar(50) OUTPUT',
#rangeMinOUT=#rangeMin OUTPUT, #rangeMaxOUT=#rangeMax OUTPUT;
END
SET #intervalSize = (#rangeMax - #rangeMin)/#numOfBreaks;
SET #SQLQuery = N'
INSERT INTO #output (lowerBound, upperBound, [count])
SELECT '+CONVERT(nvarchar, #rangeMin)+'+'+CONVERT(nvarchar, #intervalSize)+'*FLOOR(number/'+CONVERT(nvarchar, #intervalSize)+') AS lowerBound,
'+CONVERT(nvarchar, #rangeMin)+'+'+CONVERT(nvarchar, #intervalSize)+'*FLOOR(number/'+CONVERT(nvarchar, #intervalSize)+')+'+CONVERT(nvarchar, #intervalSize)+' AS upperBound,
COUNT(*) AS [count]
FROM (
-- Special Case the max values.
SELECT ISNULL(NULLIF('+#numericColumnName+', '+CONVERT(nvarchar, #rangeMax)+'), '+CONVERT(nvarchar, #rangeMax)+' - 0.5 * '+CONVERT(nvarchar, #intervalSize)+') - '+CONVERT(nvarchar, #rangeMin)+' AS number
FROM '+#tableName+'
) AS B
GROUP BY FLOOR(number/'+CONVERT(nvarchar, #intervalSize)+');'
-- Return the results above
RETURN;
END;
GO