SQL aggregate functions

SQL aggregate functions aggregate values in a specified column for each group or SQL partition and return a single row per group containing the aggregate value.

• General aggregate functions
  • array_agg
  • avg
  • count
  • max
  • mean
  • median
  • min
  • sum
• Statistical aggregate functions
  • corr
  • covar
  • covar_pop
  • covar_samp
  • stddev
  • stddev_pop
  • stddev_samp
  • var
  • var_pop
  • var_samp
• Approximate aggregate functions
  • approx_distinct
  • approx_median
  • approx_percentile_cont
  • approx_percentile_cont_with_weight

General aggregate functions

• array_agg
• avg
• count
• max
• mean
• median
• min
• sum

array_agg

Returns an array created from the expression elements.

array_agg(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT
  room,
  array_agg(temp)[3] AS '3rd_temp'
FROM home
GROUP BY room

avg

Returns the average of numeric values in the specified column.

avg(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

Aliases

• mean

SELECT 
  location,
  avg(water_level) AS water_level_avg
FROM h2o_feet
GROUP BY location

count

Returns the number of rows in the specified column.

Count includes null values in the total count. To exclude null values from the total count, include <column> IS NOT NULL in the WHERE clause.

count(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT 
  location,
  count(water_level) AS water_level_count
FROM h2o_feet
GROUP BY location

max

Returns the maximum value in the specified column.

max(expression)

To return both the maximum value and its associated timestamp, use selector_max.

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT 
  location,
  max(water_level) AS water_level_max
FROM h2o_feet
GROUP BY location

mean

Alias of avg.

median

Returns the median value in the specified column.

median(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT 
  location,
  median(water_level) AS water_level_max
FROM h2o_feet
GROUP BY location

min

Returns the minimum value in the specified column.

min(expression)

To return both the minimum value and its associated timestamp, use selector_max.

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT 
  location,
  min(water_level) AS water_level_min
FROM h2o_feet
GROUP BY location

sum

Returns the sum of all values in the specified column.

sum(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT 
  location,
  sum(water_level) AS water_level_sum
FROM h2o_feet
GROUP BY location

Statistical aggregate functions

• corr
• covar
• covar_pop
• covar_samp
• stddev
• stddev_pop
• stddev_samp
• var
• var_pop
• var_samp

corr

Returns the coefficient of correlation between two numeric values.

corr(expression1, expression2)

Arguments

• expression1: First column or literal value to operate on.
• expression2: Second column or literal value to operate on.

SELECT
  room,
  corr(hum, temp) AS correlation
FROM home
GROUP BY room

covar

Returns the covariance of a set of number pairs.

covar(expression1, expression2)

Arguments

• expression1: First column or literal value to operate on.
• expression2: Second column or literal value to operate on.

SELECT
  room,
  covar(hum, temp) AS covar
FROM home
GROUP BY room

covar_pop

Returns the population covariance of a set of number pairs.

covar_pop(expression1, expression2)

Arguments

• expression1: First column or literal value to operate on.
• expression2: Second column or literal value to operate on.

SELECT
  room,
  covar_pop(hum, temp) AS covar_pop
FROM home
GROUP BY room

covar_samp

Returns the sample covariance of a set of number pairs.

covar_samp(expression1, expression2)

Arguments

• expression1: First column or literal value to operate on.
• expression2: Second column or literal value to operate on.

SELECT
  room,
  covar_samp(hum, temp) AS covar_samp
FROM home
GROUP BY room

stddev

Returns the standard deviation of a set of numbers.

stddev(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT
  room,
  stddev(co) AS stddev
FROM home
GROUP BY room

stddev_pop

Returns the population standard deviation of a set of numbers.

stddev_pop(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT
  room,
  stddev_pop(co) AS stddev_pop
FROM home
GROUP BY room

stddev_samp

Returns the sample standard deviation of a set of numbers.

stddev_samp(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT
  room,
  stddev_samp(co) AS stddev_samp
FROM home
GROUP BY room

var

Returns the statistical variance of a set of numbers.

var(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT
  room,
  var(co) AS var
FROM home
GROUP BY room

var_pop

Returns the statistical population variance of a set of numbers.

var_pop(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT
  room,
  var_pop(co) AS var_pop
FROM home
GROUP BY room

var_samp

Returns the statistical sample variance of a set of numbers.

var_samp(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT
  room,
  var_samp(co) AS var_samp
FROM home
GROUP BY room

Approximate aggregate functions

• approx_distinct
• approx_median
• approx_percentile_cont
• approx_percentile_cont_with_weight

approx_distinct

Returns the approximate number of distinct input values calculated using the HyperLogLog algorithm.

approx_distinct(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT
  room,
  approx_distinct(co::string) AS approx_distinct
FROM home
GROUP BY room

approx_median

Returns the approximate median (50th percentile) of input values. It is an alias of approx_percentile_cont(x, 0.5).

approx_median(expression)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

SELECT
  room,
  approx_median(temp) AS approx_median
FROM home
GROUP BY room

approx_percentile_cont

Returns the approximate percentile of input values using the t-digest algorithm.

approx_percentile_cont(expression, percentile, centroids)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.

• percentile: Percentile to compute. Must be a float value between 0 and 1 (inclusive).

• centroids: Number of centroids to use in the t-digest algorithm. Default is 100.

  If there are this number or fewer unique values, you can expect an exact result. A higher number of centroids results in a more accurate approximation, but requires more memory to compute.

SELECT
  room,
  approx_percentile_cont(temp, 0.99) AS "99th_percentile"
FROM home
GROUP BY room

approx_percentile_cont_with_weight

Returns the weighted approximate percentile of input values using the t-digest algorithm.

approx_percentile_cont_with_weight(expression, weight, percentile)

Arguments

• expression: Expression to operate on. Can be a constant, column, or function, and any combination of arithmetic operators.
• weight: Expression to use as weight. Can be a constant, column, or function, and any combination of arithmetic operators.
• percentile: Percentile to compute. Must be a float value between 0 and 1 (inclusive).

SELECT
  room,
  approx_percentile_cont_with_weight(temp, co, 0.99) AS "co_weighted_99th_percentile"
FROM home
GROUP BY room