ahmad48 بتاريخ: 23 يوليو 2010 تقديم بلاغ مشاركة بتاريخ: 23 يوليو 2010 [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. اقتباس رابط هذا التعليق شارك المزيد من خيارات المشاركة
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