Aggregate Functions
Examples
-- produce a single row containing the sum of the "amount" column
SELECT SUM(amount) FROM sales;
-- produce one row per unique region, containing the sum of "amount" for each group
SELECT region, SUM(amount) FROM sales GROUP BY region;
-- return only the regions that have a sum of "amount" higher than 100
SELECT region FROM sales GROUP BY region HAVING SUM(amount) > 100;
-- return the number of unique values in the "region" column
SELECT COUNT(DISTINCT region) FROM sales;
-- return two values, the total sum of "amount" and the sum of "amount" minus columns where the region is "north"
SELECT SUM(amount), SUM(amount) FILTER (region != 'north') FROM sales;
-- returns a list of all regions in order of the "amount" column
SELECT LIST(region ORDER BY amount DESC) FROM sales;
Syntax
Aggregates are functions that combine multiple rows into a single value. Aggregates are different from scalar functions and window functions because they change the cardinality of the result. As such, aggregates can only be used in the SELECT and HAVING clauses of a SQL query.
When the DISTINCT clause is provided, only distinct values are considered in the computation of the aggregate. This is typically used in combination with the COUNT aggregate to get the number of distinct elements; but it can be used together with any aggregate function in the system.
When the ORDER BY clause is provided, the values being aggregated are sorted before applying the function.
Usually this is not important, but there are some order-sensitive aggregates that can have indeterminate results
(e.g., first, last, list and string_agg). These can be made deterministic by ordering the arguments.
For order-insensitive aggregates, this clause is parsed and applied, which is inefficient, but still produces the same result.
General Aggregate Functions
The table below shows the available general aggregate functions.
| Function | Description | Example | Alias(es) |
|---|---|---|---|
any_value(arg) | Returns the first non-null value from arg. | any_value(A) | - |
arg_max(arg,val) | Finds the row with the maximum val. Calculates the arg expression at that row. | arg_max(A,B) | argMax(A,B), max_by(A,b) |
arg_min(arg,val) | Finds the row with the minimum val. Calculates the arg expression at that row. | arg_min(A,B) | argMin(A,B), min_by(A,B) |
avg(arg) | Calculates the average value for all tuples in arg. | avg(A) | - |
bit_and(arg) | Returns the bitwise AND of all bits in a given expression . | bit_and(A) | - |
bit_or(arg) | Returns the bitwise OR of all bits in a given expression. | bit_or(A) | - |
bit_xor(arg) | Returns the bitwise XOR of all bits in a given expression. | bit_xor(A) | - |
bitstring_agg(arg) | Returns a bitstring with bits set for each distinct value. | bitstring_agg(A) | - |
bool_and(arg) | Returns TRUE if every input value is TRUE, otherwise FALSE. | bool_and(A) | - |
bool_or(arg) | Returns TRUE if any input value is TRUE, otherwise FALSE. | bool_or(A) | - |
count(arg) | Calculates the number of tuples tuples in arg. | count(A) | - |
favg(arg) | Calculates the average using a more accurate floating point summation (Kahan Sum). | favg(A) | - |
first(arg) | Returns the first value of a column. | first(A) | arbitrary(A) |
fsum(arg) | Calculates the sum using a more accurate floating point summation (Kahan Sum). | fsum(A) | sumKahan, kahan_sum |
histogram(arg) | Returns a LIST of STRUCTs with the fields bucket and count. | histogram(A) | - |
last(arg) | Returns the last value of a column. | last(A) | - |
list(arg) | Returns a LIST containing all the values of a column. | list(A) | array_agg |
max(arg) | Returns the maximum value present in arg. | max(A) | - |
min(arg) | Returns the minumum value present in arg. | min(A) | - |
product(arg) | Calculates the product of all tuples in arg | product(A) | - |
string_agg(arg, sep) | Concatenates the column string values with a separator | string_agg(S, ',') | group_concat |
sum(arg) | Calculates the sum value for all tuples in arg. | sum(A) | - |
Approximate Aggregates
The table below shows the available approximate aggregate functions.
| Function | Description | Example |
|---|---|---|
approx_count_distinct(x) | Gives the approximate count of distintinct elements using HyperLogLog. | approx_count_distinct(A) |
approx_quantile(x,pos) | Gives the approximate quantile using T-Digest. | approx_quantile(A,0.5) |
reservoir_quantile(x,quantile,sample_size=8192) | Gives the approximate quantile using reservoir sampling, the sample size is optional and uses 8192 as a default size. | reservoir_quantile(A,0.5,1024) |
Statistical Aggregates
The table below shows the available statistical aggregate functions.
| Function | Description | Formula | Alias |
|---|---|---|---|
corr(y,x) | Returns the correlation coefficient for non-null pairs in a group. | COVAR_POP(y, x) / (STDDEV_POP(x) * STDDEV_POP(y)) | - |
covar_pop(y,x) | Returns the population covariance of input values. | (SUM(x*y) - SUM(x) * SUM(y) / COUNT(*)) / COUNT(*) | - |
entropy(x) | Returns the log-2 entropy of count input-values. | - | - |
kurtosis(x) | Returns the excess kurtosis (Fisher's definition) of all input values, with a bias correction according to the sample size. | - | - |
mad(x) | Returns the median absolute deviation for the values within x. NULL values are ignored. Temporal types return a positive INTERVAL. | MEDIAN(ABS(x-MEDIAN(x))) | - |
median(x) | Returns the middle value of the set. NULL values are ignored. For even value counts, quantitiative values are averaged and ordinal values return the lower value. | QUANTILE_CONT(x, 0.5) | - |
mode(x) | Returns the most frequent value for the values within x. NULL values are ignored. | - | - |
quantile_cont(x,pos) | Returns the intepolated quantile number between 0 and 1 . If pos is a LIST of FLOATs, then the result is a LIST of the corresponding intepolated quantiles. | - | - |
quantile_disc(x,pos) | Returns the exact quantile number between 0 and 1 . If pos is a LIST of FLOATs, then the result is a LIST of the corresponding exact quantiles. | - | quantile |
regr_avgx(y,x) | Returns the average of the independent variable for non-null pairs in a group, where x is the independent variable and y is the dependent variable. | - | - |
regr_avgy(y,x) | Returns the average of the dependent variable for non-null pairs in a group, where x is the independent variable and y is the dependent variable. | - | - |
regr_count(y,x) | Returns the number of non-null number pairs in a group. | (SUM(x*y) - SUM(x) * SUM(y) / COUNT(*)) / COUNT(*) | - |
regr_intercept(y,x) | Returns the intercept of the univariate linear regression line for non-null pairs in a group. | AVG(y)-REGR_SLOPE(y,x)*AVG(x) | - |
regr_r2(y,x) | Returns the coefficient of determination for non-null pairs in a group. | - | - |
regr_slope(y,x) | Returns the slope of the linear regression line for non-null pairs in a group. | COVAR_POP(x,y) / VAR_POP(x) | - |
regr_sxx(y,x) | - | REGR_COUNT(y, x) * VAR_POP(x) | - |
regr_sxy(y,x) | Returns the population covariance of input values. | REGR_COUNT(y, x) * COVAR_POP(y, x) | - |
regr_syy(y,x) | - | REGR_COUNT(y, x) * VAR_POP(y) f | - |
skewness(x) | Returns the skewness of all input values. | - | - |
stddev_pop(x) | Returns the population standard deviation. | sqrt(var_pop(x)) | - |
stddev_samp(x) | Returns the sample standard deviation. | sqrt(var_samp(x)) | stddev(x) |
var_pop(x) | Returns the population variance. | - | - |
var_samp(x) | Returns the sample variance of all input values. | (SUM(x^2) - SUM(x)^2 / COUNT(x)) / (COUNT(x) - 1) | variance(arg,val) |
Ordered Set Aggregate Functions
The table below shows the available "ordered set" aggregate functions.
These functions are specified using the WITHIN GROUP(ORDER BY sort_expression) syntax,
and they are converted to an equivalent aggregate function that takes the ordering expression
as the first argument.
| Function | Equivalent |
|---|---|
mode() WITHIN GROUP (ORDER BY sort_expression) | mode(sort_expression) |
percentile_cont(fraction) WITHIN GROUP (ORDER BY sort_expression) | quantile_cont(sort_expression, fraction) |
percentile_cont(fractions) WITHIN GROUP (ORDER BY sort_expression) | quantile_cont(sort_expression, fractions) |
percentile_disc(fraction) WITHIN GROUP (ORDER BY sort_expression) | quantile_disc(sort_expression, fraction) |
percentile_disc(fractions) WITHIN GROUP (ORDER BY sort_expression) | quantile_disc(sort_expression, fractions) |