postgresql----聚合函數

聚合函數是從一組輸入中計算出一個結果的函數。

測試表

test=# \d tbl_test
          Table "public.tbl_test"
 Column |         Type          | Modifiers 
--------+-----------------------+-----------
 id     | integer               | 
 name   | character varying(32) | 
 sex    | character varying(1)  | 

test=# select * from tbl_test;
 id | name | sex 
----+------+-----
  1 | 張三 | m
  2 | 李四 | m
  3 | 王五 | f
(3 rows)

 

通用聚合函數

函數	參數類型	返回類型	描述	示例	結果
array_agg(expression)	任意非數組類型	參數類型的數組	將入參包括NULL鏈接成一個數組	select array_agg(id) from tbl_test;	{1,2,3}
array_agg(expression)	任意數組類型	入參數據類型	將入參數組鏈接成更高維度的數組，輸入的數組必須是相同的維度，且不容許是空或NULL	select array_agg(array['b','c','a']);	{{b,c,a}}
avg(expression)	smallint, int, bigint, real, double precision, numeric, or interval	整形返回numeric，浮點型返回double precision，其餘和入參類型相同	平均值	select avg(id) from tbl_test;	2.0000000000000000
bit_and(expression)	smallint, int, bigint, or bit	和入參類型相同	全部非NULL輸入值的按位與，若是全爲NULL則返回NULL	select bit_and(id) from tbl_test;	0
bit_or(expression)	smallint, int, bigint, or bit	和入參類型相同	全部非NULL輸入值的按位或，若是全爲NULL則返回NULL	select bit_or(id) from tbl_test;	3
bool_and(expression)	bool	bool	若是輸入全是true則返回true，不然爲false	select bool_or(id::bool) from tbl_test;	t
bool_or(expression)	bool	bool	若是輸入至少一個true，則返回true，不然返回false	select bool_or((id-1)::bool) from tbl_test;	t
count(*)		bigint	輸入行數	select count(*) from tbl_test;	3
count(expression)	any	bigint	輸入行中非NULL的行數	select count(id) from tbl_test;	3
every(expression)	bool	bool	功能同bool_and
json_agg(expression)	any	json	將輸入聚合成一個json數組	select json_agg(id) from tbl_test;	[1, 2, 3]
jsonb_agg(expression)	any	jsonb	將輸入聚合成一個json數組	select jsonb_agg(id) from tbl_test;	[1, 2, 3]
json_object_agg(name,value)	(any, any)	json	將輸入組成一個key/value對的json對象	select json_object_agg('a','one');	{ "a" : "one" }
jsonb_object_agg(name,value)	(any, any)	jsonb	將輸入組成一個key/value對的json對象	select jsonb_object_agg('a','one');	{"a": "one"}
max(expression)			輸入最大值	select max(id) from tbl_test;	3
min(expression)			輸入最小值	select min(id) from tbl_test;	1
string_agg(expression,delimiter)	(text, text) or (bytea, bytea)	同參數類型	將輸入使用delimiter鏈接成一個text	select string_agg(name,',') from tbl_test;	張三,李四,王五
sum(expression)	smallint, int, bigint, real, double precision, numeric, interval, or money		輸入和	select sum(id) from tbl_test;	6
xmlagg(expression)	xml	xml		請參考xml類型及其函數

 

修改表

test=# alter table tbl_test add column id1 int default 1;
ALTER TABLE
test=# select * from tbl_test;
 id | name | sex | id1 
----+------+-----+-----
  1 | 張三 | m   |   1
  2 | 李四 | m   |   1
  3 | 王五 | f   |   1
(3 rows)

 

統計聚合函數

函數	參數類型	返回類型	描述	示例	結果
corr(Y, X)	double precision	double precision	相關係數	select corr(id,id) from tbl_test;	1
covar_pop(Y, X)	double precision	double precision	整體協方差	select covar_pop(id,id) from tbl_test;	0.666666666666667
covar_samp(Y, X)	double precision	double precision	樣本協方差	select covar_samp(id,id1) from tbl_test;	0
regr_avgx(Y, X)	double precision	double precision	自變量平均值(sum(X)/N)	select regr_avgx(id,id1) from tbl_test;	1
regr_avgy(Y, X)	double precision	double precision	因變量平均值(sum(Y)/N)	select regr_avgy(id,id1) from tbl_test;	2
regr_count(Y, X)	double precision	bigint	兩個參數都不爲NULL的行數	select regr_count(id,id1) from tbl_test;	3
regr_intercept(Y, X)	double precision	double precision	根據全部輸入點(X,Y)利用最小二乘法計算一個線性方程式。而後返回該直線的Y軸截距	select regr_intercept(id,id) from tbl_test;	0
regr_r2(Y, X)	double precision	double precision	相關係數平方	select regr_r2(id,id) from tbl_test;	1
regr_slope(Y, X)	double precision	double precision	根據全部輸入點(X,Y)利用最小二乘法計算一個線性方程式。而後返回該直線的斜率	select regr_slope(id,id) from tbl_test;	1
regr_sxx(Y, X)	double precision	double precision	sum(X^2) - sum(X)^2/N	select regr_sxx(id,id) from tbl_test;	2
regr_sxy(Y, X)	double precision	double precision	sum(X*Y) - sum(X) * sum(Y)/N	select regr_sxy(id,id) from tbl_test;	2
regr_syy(Y, X)	double precision	double precision	sum(Y^2) - sum(Y)^2/N	select regr_syy(id,id) from tbl_test;	2
stddev(expression)	smallint, int, bigint, real, double precision, or numeric	double precision for floating-point arguments, otherwise numeric	同stddev_samp
stddev_pop(expression)	smallint, int, bigint, real, double precision, or numeric	double precision for floating-point arguments, otherwise numeric	整體標準差	select stddev_pop(id) from tbl_test;	0.81649658092772603273
stddev_samp(expression)	smallint, int, bigint, real, double precision, or numeric	double precision for floating-point arguments, otherwise numeric	樣本標準差	select stddev_samp(id) from tbl_test;	1.00000000000000000000
variance(expression)	smallint, int, bigint, real, double precision, or numeric	double precision for floating-point arguments, otherwise numeric	同var_samp
var_pop(expression)	smallint, int, bigint, real, double precision, or numeric	double precision for floating-point arguments, otherwise numeric	整體方差	select var_pop(id) from tbl_test;	0.66666666666666666667
var_samp(expression)	smallint, int, bigint, real, double precision, or numeric	double precision for floating-point arguments, otherwise numeric	樣本方差	select var_samp(id) from tbl_test;	1.00000000000000000000

test=# insert into tbl_test values (2,'ww','f');
INSERT 0 1
test=# select * from tbl_test;
 id | name | sex | id1 
----+------+-----+-----
  1 | 張三 | m   |   1
  2 | 李四 | m   |   1
  3 | 王五 | f   |   1
  2 | ww   | f   |   1
(4 rows)

 

順序集聚合函數

函數	直接參數類型	聚合參數類型	返回類型	描述	示例	結果
mode() WITHIN GROUP (ORDER BYsort_expression)		任意可排序類型	同排序類型	返回最頻繁的輸入值（若是有 多個一樣頻繁的結果，則返回第一個）	select mode() within group (order by id) from tbl_test;	2
percentile_cont(fraction) WITHIN GROUP (ORDER BY sort_expression)	double precision	double precisionor interval	同排序類型	continuous percentile: returns a value corresponding to the specified fraction in the ordering, interpolating between adjacent input items if needed	select percentile_cont(0.25) WITHIN GROUP (ORDER BY id) from tbl_test;	1.75
percentile_cont(fractions) WITHIN GROUP (ORDER BY sort_expression)	double precision[]	double precisionor interval	array of sort expression's type	multiple continuous percentile: returns an array of results matching the shape of the fractionsparameter, with each non-null element replaced by the value corresponding to that percentile
percentile_disc(fraction) WITHIN GROUP (ORDER BY sort_expression)	double precision	any sortable type	same as sort expression	discrete percentile: returns the first input value whose position in the ordering equals or exceeds the specified fraction
percentile_disc(fractions) WITHIN GROUP (ORDER BY sort_expression)	double precision[]	any sortable type	array of sort expression's type	multiple discrete percentile: returns an array of results matching the shape of the fractions parameter, with each non-null element replaced by the input value corresponding to that percentile