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Aggregate functions

Atualizado em Ver como Markdown

Aggregate functions collapse multiple rows into a single result. They are used with GROUP BY to compute summaries per group, or without GROUP BY to compute a single result across all rows.

Most aggregates accept a DISTINCT modifier, for example COUNT(DISTINCT customer_id) or SUM(DISTINCT total_amount).

Basic aggregates

COUNT

Counts rows. COUNT(*) counts all rows. COUNT(column) counts non-NULL values.

SELECT COUNT(*) AS total_rows
FROM my_namespace.sales_data

SELECT department, COUNT(*) AS dept_count
FROM my_namespace.sales_data
GROUP BY department
ORDER BY dept_count DESC

SUM

Returns the sum of values in a column.

SELECT SUM(total_amount) AS grand_total
FROM my_namespace.sales_data

SELECT department, SUM(total_amount) AS dept_total
FROM my_namespace.sales_data
GROUP BY department
ORDER BY dept_total DESC

AVG

Returns the average of values in a column. Alias: mean.

SELECT AVG(total_amount) AS avg_amount
FROM my_namespace.sales_data

SELECT department, AVG(total_amount) AS avg_amount
FROM my_namespace.sales_data
GROUP BY department
ORDER BY avg_amount DESC

MIN

Returns the minimum value. Works on numeric and string columns.

SELECT MIN(total_amount) AS min_amount, MIN(customer_id) AS first_customer
FROM my_namespace.sales_data

SELECT department, MIN(total_amount) AS min_amount
FROM my_namespace.sales_data
GROUP BY department

MAX

Returns the maximum value. Works on numeric and string columns.

SELECT MAX(total_amount) AS max_amount, MAX(customer_id) AS last_customer
FROM my_namespace.sales_data

SELECT department, MAX(total_amount) AS max_amount
FROM my_namespace.sales_data
GROUP BY department

MEDIAN

Returns the exact median value. For large datasets, use approx_median instead.

SELECT MEDIAN(total_amount) AS median_amount
FROM my_namespace.sales_data

SELECT department, MEDIAN(total_amount) AS median_amount
FROM my_namespace.sales_data
GROUP BY department

PERCENTILE_CONT

Returns the exact value at a given percentile using WITHIN GROUP (ORDER BY ...). The percentile parameter must be between 0.0 and 1.0 inclusive. For large datasets, use approx_percentile_cont instead.

SELECT PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY total_amount) AS median,
       PERCENTILE_CONT(0.95) WITHIN GROUP (ORDER BY total_amount) AS p95
FROM my_namespace.sales_data

Approximate aggregates

Approximate aggregation functions produce statistically estimated results while using significantly less memory and compute than their exact counterparts. Use them when analyzing large datasets and an approximate result is acceptable.

approx_percentile_cont

Returns the approximate value at a given percentile using a T-Digest algorithm. The percentile parameter must be between 0.0 and 1.0 inclusive.

SELECT approx_percentile_cont(total_amount, 0.5) AS median,
       approx_percentile_cont(total_amount, 0.95) AS p95
FROM my_namespace.sales_data

SELECT department,
       approx_percentile_cont(total_amount, 0.5) AS median
FROM my_namespace.sales_data
GROUP BY department
ORDER BY median DESC

approx_percentile_cont_with_weight

Returns the approximate weighted percentile. Rows are weighted by the weight column.

SELECT approx_percentile_cont_with_weight(unit_price, quantity, 0.5) AS weighted_median
FROM my_namespace.sales_data
WHERE unit_price IS NOT NULL AND quantity IS NOT NULL

approx_median

Returns the approximate median. Equivalent to approx_percentile_cont(column, 0.5).

SELECT approx_median(total_amount) AS median_amount
FROM my_namespace.sales_data

SELECT department, approx_median(total_amount) AS median
FROM my_namespace.sales_data
GROUP BY department

approx_distinct

Returns the approximate count of distinct values using HyperLogLog.

SELECT approx_distinct(customer_id) AS unique_customers
FROM my_namespace.sales_data

SELECT department, approx_distinct(customer_id) AS unique_customers
FROM my_namespace.sales_data
GROUP BY department

approx_top_k

Returns the k most frequent values with their approximate counts.

SELECT approx_top_k(department, 5) AS top_departments
FROM my_namespace.sales_data

Statistical aggregates

var / var_samp

Returns the sample variance.

SELECT var(total_amount) AS variance
FROM my_namespace.sales_data

SELECT department, var(total_amount) AS variance
FROM my_namespace.sales_data
GROUP BY department

var_pop

Returns the population variance.

SELECT var_pop(total_amount) AS pop_variance
FROM my_namespace.sales_data

stddev / stddev_samp

Returns the sample standard deviation.

SELECT stddev(total_amount) AS std_dev
FROM my_namespace.sales_data

SELECT department, stddev(total_amount) AS std_dev
FROM my_namespace.sales_data
GROUP BY department

stddev_pop

Returns the population standard deviation.

SELECT stddev_pop(total_amount) AS pop_std_dev
FROM my_namespace.sales_data

covar_samp

Returns the sample covariance. Alias: covar.

SELECT covar_samp(total_amount, CAST(quantity AS DOUBLE)) AS covariance
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

covar_pop

Returns the population covariance.

SELECT covar_pop(total_amount, CAST(quantity AS DOUBLE)) AS pop_covariance
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

corr

Returns the Pearson correlation coefficient between two columns.

SELECT corr(total_amount, CAST(quantity AS DOUBLE)) AS correlation
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

regr_slope

Returns the slope of the linear regression line.

SELECT regr_slope(total_amount, CAST(quantity AS DOUBLE)) AS slope
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

regr_intercept

Returns the y-intercept of the linear regression line.

SELECT regr_intercept(total_amount, CAST(quantity AS DOUBLE)) AS intercept
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

regr_count

Returns the count of non-NULL pairs.

SELECT regr_count(total_amount, CAST(quantity AS DOUBLE)) AS pair_count
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

regr_r2

Returns the coefficient of determination (R-squared).

SELECT regr_r2(total_amount, CAST(quantity AS DOUBLE)) AS r_squared
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

regr_avgx

Returns the average of the independent variable (x) for non-NULL pairs.

SELECT regr_avgx(total_amount, CAST(quantity AS DOUBLE)) AS avg_qty
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

regr_avgy

Returns the average of the dependent variable (y) for non-NULL pairs.

SELECT regr_avgy(total_amount, CAST(quantity AS DOUBLE)) AS avg_amount
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

regr_sxx

Returns the sum of squares of the independent variable.

SELECT regr_sxx(total_amount, CAST(quantity AS DOUBLE)) AS sxx
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

regr_syy

Returns the sum of squares of the dependent variable.

SELECT regr_syy(total_amount, CAST(quantity AS DOUBLE)) AS syy
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

regr_sxy

Returns the sum of products of the paired variables.

SELECT regr_sxy(total_amount, CAST(quantity AS DOUBLE)) AS sxy
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL AND quantity IS NOT NULL

Bitwise aggregates

bit_and

Returns the bitwise AND of all values in a group.

SELECT department, bit_and(quantity) AS and_result
FROM my_namespace.sales_data
WHERE quantity IS NOT NULL
GROUP BY department

bit_or

Returns the bitwise OR of all values in a group.

SELECT department, bit_or(quantity) AS or_result
FROM my_namespace.sales_data
WHERE quantity IS NOT NULL
GROUP BY department

bit_xor

Returns the bitwise XOR of all values in a group.

SELECT department, bit_xor(quantity) AS xor_result
FROM my_namespace.sales_data
WHERE quantity IS NOT NULL
GROUP BY department

Boolean aggregates

bool_and

Returns true if all values in a group are true.

SELECT department, bool_and(is_completed) AS all_completed
FROM my_namespace.sales_data
WHERE is_completed IS NOT NULL
GROUP BY department

bool_or

Returns true if any value in a group is true.

SELECT department, bool_or(is_completed) AS any_completed
FROM my_namespace.sales_data
WHERE is_completed IS NOT NULL
GROUP BY department

Positional aggregates

first_value

Returns the first value in a group according to the specified ordering.

SELECT department,
       first_value(customer_id ORDER BY total_amount ASC) AS lowest_spender
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL
GROUP BY department

last_value

Returns the last value in a group according to the specified ordering.

SELECT department,
       last_value(customer_id ORDER BY total_amount ASC) AS highest_spender
FROM my_namespace.sales_data
WHERE total_amount IS NOT NULL
GROUP BY department

Collection aggregates

These aggregates accumulate all input values into a single result. Because they hold every value in memory, use a WHERE filter or GROUP BY to keep group sizes bounded on large datasets.

array_agg

Collects values from a group into an array.

SELECT department, array_agg(customer_id) AS customers
FROM my_namespace.sales_data
GROUP BY department

string_agg

Concatenates values from a group into a single string, separated by the given delimiter.

SELECT department, string_agg(customer_id, ', ') AS customer_list
FROM my_namespace.sales_data
GROUP BY department