SQL Server 2000
DECLARE @Sample TABLE
x INT NOT NULL,
y INT NOT NULL
VALUES (3, 9),
;WITH cteSource(x, xAvg, y, yAvg, n)
SELECT 1E * x,
AVG(1E * x) OVER (PARTITION BY (SELECT NULL)),
1E * y,
AVG(1E * y) OVER (PARTITION BY (SELECT NULL)),
COUNT(*) OVER (PARTITION BY (SELECT NULL))
SELECT SUM((x - xAvg) *(y - yAvg)) / MAX(n) AS [COVAR(x,y)]
Today I had the opportunity to debug a system with a client. I have to confess it took a while to figure out the bug, but here it is
SELECT COUNT(*) OfflineData
Do you see the bug?
Yes, there should be a FROM clause before the table name. Without the from clause, SQL Server treats the name as an alias for the count column. And what do the COUNT always return in this case?
It returns 1.
So the bug had a severe implication. Now I now it's easy to forget to write a FROM in your query. How can we avoid these stupid mistakes?
CREATE FUNCTION dbo.fnConvertUtf8Ansi
DECLARE @Value SMALLINT = 160,
IF @Source NOT LIKE '%[ÂÃ]%'
WHILE @Value <= 255
SELECT @Utf8 = CASE
WHEN @Value BETWEEN 160 AND 191 THEN CHAR(194) + CHAR(@Value)
WHEN @Value BETWEEN 192 AND 255 THEN CHAR(195) + CHAR(@Value - 64)
@Ansi = CHAR(@Value)
WHILE CHARINDEX(@Source, @Utf8) > 0
SET @Source = REPLACE(@Source, @Utf8, @Ansi)
SET @Value += 1
CREATE FUNCTION dbo.fnIsOnMonthEdge
RETURN CASE @theDate
WHEN '99991231' THEN 1
ELSE DATEDIFF(MONTH, @theDate, DATEADD(DAY, 1, @theDate))
WHEN '17530101' THEN -1
ELSE DATEDIFF(MONTH, @theDate, DATEADD(DAY, -1, @theDate))
Today I finished my presentation about finding a unified algorithm for Relational Division, which should work for all types of division; singlerecord and multirecord, singlecolumn and multicolumn and both exact division and with remainder.
Optionally it should work with single and multiple divisor sets. That's 16 permutations of relational division kinds.
A bonus point is that the algorithm I've found work across multiple platforms with standard SQL language elements.
Also, I have performance tested the algorithm with the sample data from Mr Celko here.
For such small sample set, my algorithm is in the top queries, but the real performance kicks in when you...
SUBSTRING(BinaryFormat, 1, 2) AS DayPart,
SUBSTRING(BinaryFormat, 3, 2) AS TimePart,
CAST(SUBSTRING(BinaryFormat, 1, 2) AS INT) AS [Days],
DATEADD(DAY, CAST(SUBSTRING(BinaryFormat, 1, 2) AS INT), 0) AS [Today],
SUBSTRING(BinaryFormat, 3, 2) AS [Ticks],
DATEADD(MINUTE, CAST(SUBSTRING(BinaryFormat, 3, 2) AS SMALLINT), 0) AS Peso
SELECT CAST(GETDATE() AS SMALLDATETIME) AS [Now],
CAST(CAST(GETDATE() AS SMALLDATETIME) AS BINARY(4)) AS BinaryFormat
) AS d
SUBSTRING(BinaryFormat, 1, 4) AS DayPart,
SUBSTRING(BinaryFormat, 5, 4) AS TimePart,
CAST(SUBSTRING(BinaryFormat, 1, 4) AS INT) AS [Days],
DATEADD(DAY, CAST(SUBSTRING(BinaryFormat, 1, 4) AS INT), 0) AS [Today],
CAST(SUBSTRING(BinaryFormat, 5, 4) AS INT) AS [Ticks],
DATEADD(MILLISECOND, 1000.E / 300.E * CAST(SUBSTRING(BinaryFormat, 5, 4) AS INT), 0) AS Peso
SELECT GETDATE() AS [Now],
CAST(GETDATE() AS BINARY(8)) AS BinaryFormat
) AS d
CREATE FUNCTION dbo.fnGetEasterDate
SELECT DATEADD(DAY, DATEDIFF(DAY, 0, CONVERT(DATETIME, CAST(@Year AS CHAR(4)) + BaseDate, 112)) / 7 * 7, 6)
SELECT CASE @Year % 19
WHEN 0 THEN '0415'
WHEN 1 THEN '0404'
WHEN 2 THEN '0324'
WHEN 3 THEN '0412'
WHEN 4 THEN '0401'
WHEN 5 THEN '0419'
WHEN 6 THEN '0409'
WHEN 7 THEN '0329'
WHEN 8 THEN '0417'
WHEN 9 THEN '0406'
WHEN 10 THEN '0326'
WHEN 11 THEN '0414'
WHEN 12 THEN '0403'
WHEN 13 THEN '0323'
WHEN 14 THEN '0411'
WHEN 15 THEN '0331'
WHEN 16 THEN '0418'
I got an email from Mr Celko and he correctly stated that my previous solution was not truly working with sets, so he posted me some solutions and proper sample data.
With this information at my hand, I started to investigate what really is needed to get this Relational Division to work properly with two sets; Dividend and Divisor.
Some of you know me well, and know I am not satisfied with just solving the problem. There have to be some tweaks, and I did that too with this solution. Not only is it only touching the Dividend table once and...
I came across an interesting post on Microsoft SQL Server forum this afternoon. It was a question about Relational algebra and the poster wanted to have an efficient query to solve his problem.
The problem could be solved with relational division, but there is no such operator in SQL Server. Maybe there will be some day.
For a fully working solution, see http://weblogs.sqlteam.com/peterl/archive/2010/07/02/Proper-Relational-Division-With-Sets.aspx
But for now there is no such operator, so we as developers have to find our own ways.
First prepare and populate some sample data
-- Prepare sample data
DECLARE @Sample TABLE
ParentID INT NOT NULL,
Keyword VARCHAR(25) NOT NULL,
UNIQUE (ParentID, Keyword)
-- Populate sample data
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