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#1 ahmad48

ahmad48

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تاريخ المشاركة 23 July 2010 - 10:27 AM

[سم الله الرحمن الرحيم

اخواني ممكن حدى يشرحلنا ما الهدف من كل دالة من الدوال الاتية وفيما تستخدم

[b]Statistical Function Calculators[/b]


STDDEV(<expression>)
. The standard deviation is the average difference
from the mean. The mean is similar to the average.

VARIANCE(<expression>)
. The variance is the square of the standard
deviation and, thus, the average squared difference from the
mean, or the squared average deviation from the mean.

STDDEV_POP(<expression>)
. The population standard deviation.

STDDEV_SAMP(<expression>)
. The sample standard deviation.

VAR_POP(<expression>)
. The population variance, excluding
NULL values.

VAR_SAMP(<expression>)
. The sample variance, excluding NULL
values.


COVAR_POP(<expression>, <expression>)
. The population covariance
of two expressions. The covariance is the average product of
differences from two group means.

COVAR_SAMP(<expression>, <expression>)
. The sample covariance
of two expressions.

CORR(<expression>, <expression>)
. The coefficient of correlation
of two expressions. A correlation coefficient assesses the quality of a
least squares fitting to the data. The least squares procedure finds the
best fitting curve to a given set of values.

REGR_[ SLOPE | INTERCEPT | COUNT | R2 | AVGX| AVGY |
SXX | SYY | SXY ](<expression>, <expression>)
. Linear regression
functions fit a least-squares regression line to two expressions. Linear
regression is used to make predictions about a single value. Simple
linear regression involves discovering the equation for a straight line
that most nearly fits the given data. The discovered linear equation is
then used to predict values for the data. A linear regression curve is a
straight line through a set of plotted points. The straight line should
get as close as possible to all points at once—a best fit!

CORR_{S | K}
. This function calculates Pearson’s correlation coefficient,
measuring the strength of a linear relationship between two
variables. Plotting two variables on a graph results in a lot of dots
plotted from two axes. Pearson’s correlation coefficient can tell you
how good the straight line is.

MEDIAN
. A median is a middle or interpolated value. Quite literally,
a median is the value in the middle of a set of values. If a distribution
is discontinuous and skewed, or just all over the place, then
the median will not be anywhere near a mean or average of a set of
values. A median is not always terribly useful.

STATS_{BINOMIAL_TEST | CROSSTAB | F_TEST | KS_TEST
| MODE | MW_TEST | ONE_WAY_ANOVA | STATS_T_TEST_*
| STATS_WSR_TEST}
. These functions provide various statistical
goodies.


[b]Statistical Distribution Functions[/b]


CUME_DIST(<expression> [, <expression> . . . ]) WITHIN
GROUP (ORDER BY <expression> [, <expression>])
. The cumulative
distribution of an expression within a group of values.


PERCENTILE_{ CONT | DISC }(<expression>) WITHIN
GROUP (ORDER BY <expression>)
. The percent point function
or the inverse distribution function for a
CONT
inuous or
DISC
rete
distribution. Since the percent point function is an inverse distribution
function, we start with the probability and compute the corresponding
value for the cumulative distribution


[b]Ranking Functions[/b]


RANK(<expression> [, <expression> . . . ]) WITHIN GROUP
(ORDER BY <expression> [, <expression>])
. The rank of a value
in a group of values.

DENSE_RANK(<expression> [, <expression> . . . ]) WITHIN
GROUP (ORDER BY <expression> [, <expression> . . . ])
. The
rank of a row within an ordered group of rows.

PERCENT_RANK(<expression> [, <expression> . . . ]) WITHIN
GROUP (ORDER BY [, <expression> . . . ]). Similar to a cumulative
distribution function, where the rank produced is a percentage
of the current value’s rank in relation to the rank of the highest
ranked value.
 NTILE(<expression>) OVER . . . Split a sorted row set into equally
sized groups or buckets.
 ROW_NUMBER() OVER . . . Adds a unique integer to each row in
a row set.
 FIRST | LAST (<expression> [, <expression> . . . ]) WITHIN
GROUP (ORDER BY <expression> [, <expression> . . . ]). Works
with only the first and last ranking rows in a sorted group of rows.


[b]Lag and Lead Functions[/b]

 LAG | LEAD (<expression> [, <offset> ] [, <default> ]) OVER
(<expression> (ORDER BY <expression> [, <expression> . . . ]).
Access to rows at an offset count from the current row.


[b]Aggregation Functions Allowing Analysis[/b]

 COUNT, SUM, AVG, MIN, and MAX.
 FIRST_VALUE and LAST_VALUE. (return moving window first
and last row values).
 STDDEV, VARIANCE, and CORR.
 STDDEV_POP, VAR_POP, and COVAR_POP.
 STDDEV_SAMP, VAR_SAMP, and COVAR_SAMP.