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27 lines
978 B
Plaintext
27 lines
978 B
Plaintext
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Statistical Functions
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By the SQL specification, some statistical functions are defined.
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Function about variance and standard deviation are bellow.
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VAR_POP: return the population variance.
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VAR_SAMP: return the sample variance.
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STDDEV_SAMP: return the sample standard deviation .
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STDDEV_POP: return the population standard deviation.
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VAR_POP(<expr>) is equivalent to (SUM(<expr> ^ 2) - SUM(<expr>) ^ 2 / COUNT(<expr>)) / COUNT(<expr>).
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VAR_SAMP(<expr>) is equivalent to (SUM(<expr> ^ 2) - SUM(<expr>) ^ 2 / COUNT(<expr>)) / (COUNT(<expr>) - 1).
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STDDEV_POP(<expr>) is equivalent to SQRT(VAR_POP(<expr>)).
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STDDEV_SAMP(<expr>) is equivalent to SQRT(VAR_SAMP(<expr)).
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Author:
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Hajime Nakagami <nakagami@gmail.com>
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Syntax:
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<statistical function> ::= <statistical function name>(<expr>)
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<statistical function name> := { VAR_POP | VAR_SAMP | STDDEV_POP | STDDEV_SAMP }
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Example:
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SELECT STDDEV_SAMP(salary) FROM employees;
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