An aggregate function that returns the average value from a set of numbers. Its single argument can be numeric column, or the numeric result of a function or expression applied to the column value. Rows with a NULL value for the specified column are ignored. If the table is empty, or all the values supplied to AVG are NULL, AVG returns NULL.

When the query contains a GROUP BY clause, returns one value for each combination of grouping values.

Return type: DOUBLE

Examples:

-- Average all the non-NULL values in a column.
insert overwrite avg_t values (2),(4),(6),(null),(null);
-- The average of the above values is 4: (2+4+6) / 3. The 2 NULL values are ignored.
select avg(x) from avg_t;
-- Average only certain values from the column.
select avg(x) from t1 where month = 'January' and year = '2013';
-- Apply a calculation to the value of the column before averaging.
select avg(x/3) from t1;
-- Apply a function to the value of the column before averaging.
-- Here we are substituting a value of 0 for all NULLs in the column,
-- so that those rows do factor into the return value.
select avg(isnull(x,0)) from t1;
-- Apply some number-returning function to a string column and average the results.
-- If column s contains any NULLs, length(s) also returns NULL and those rows are ignored.
select avg(length(s)) from t1;
-- Can also be used in combination with DISTINCT and/or GROUP BY.
-- Return more than one result.
select month, year, avg(page_visits) from web_stats group by month, year;
-- Filter the input to eliminate duplicates before performing the calculation.
select avg(distinct x) from t1;
-- Filter the output after performing the calculation.
select avg(x) from t1 group by y having avg(x) between 1 and 20;

An aggregate function that returns the number of rows, or the number of non-NULL rows, that meet certain conditions:

• The notation COUNT(*) includes NULL values in the total.
• The notation COUNT(column_name) only considers rows where the column contains a non-NULL value.
• You can also combine COUNT with the DISTINCT operator to eliminate duplicates before counting, and to count the combinations of values across multiple columns.

When the query contains a GROUP BY clause, returns one value for each combination of grouping values.

Return type: BIGINT

Examples:

-- How many rows total are in the table, regardless of NULL values?
select count(*) from t1;
-- How many rows are in the table with non-NULL values for a column?
select count(c1) from t1;
-- Count the rows that meet certain conditions.
-- Again, * includes NULLs, so COUNT(*) might be greater than COUNT(col).
select count(*) from t1 where x > 10;
select count(c1) from t1 where x > 10;
-- Can also be used in combination with DISTINCT and/or GROUP BY.
-- Combine COUNT and DISTINCT to find the number of unique values.
-- Must use column names rather than * with COUNT(DISTINCT ...) syntax.
-- Rows with NULL values are not counted.
select count(distinct c1) from t1;
-- Rows with a NULL value in _either_ column are not counted.
select count(distinct c1, c2) from t1;
-- Return more than one result.
select month, year, count(distinct visitor_id) from web_stats group by month, year;

An aggregate function that returns a single string representing the argument value concatenated together for each row of the result set. If the optional separator string is specified, the separator is added between each pair of concatenated values.

Usage notes: concat() and concat_ws() are appropriate for concatenating the values of multiple columns within the same row, while group_concat() joins together values from different rows.

By default, returns a single string covering the whole result set. To include other columns or values in the result set, or to produce multiple concatenated strings for subsets of rows, include a GROUP BY clause in the query.

Return type: STRING

An aggregate function that returns the maximum value from a set of numbers. Opposite of the MIN function. Its single argument can be numeric column, or the numeric result of a function or expression applied to the column value. Rows with a NULL value for the specified column are ignored. If the table is empty, or all the values supplied to MAX are NULL, MAX returns NULL.

When the query contains a GROUP BY clause, returns one value for each combination of grouping values.

Return type: Same as the input argument

Examples:

-- Find the largest value for this column in the table.
select max(c1) from t1;
-- Find the largest value for this column from a subset of the table.
select max(c1) from t1 where month = 'January' and year = '2013';
-- Find the largest value from a set of numeric function results.
select max(length(s)) from t1;
-- Can also be used in combination with DISTINCT and/or GROUP BY.
-- Return more than one result.
select month, year, max(purchase_price) from store_stats group by month, year;
-- Filter the input to eliminate duplicates before performing the calculation.
select max(distinct x) from t1;

An aggregate function that returns the minimum value from a set of numbers. Opposite of the MAX function. Its single argument can be numeric column, or the numeric result of a function or expression applied to the column value. Rows with a NULL value for the specified column are ignored. If the table is empty, or all the values supplied to MIN are NULL, MIN returns NULL.

When the query contains a GROUP BY clause, returns one value for each combination of grouping values.

Return type: Same as the input argument

Examples:

-- Find the smallest value for this column in the table.
select min(c1) from t1;
-- Find the smallest value for this column from a subset of the table.
select min(c1) from t1 where month = 'January' and year = '2013';
-- Find the smallest value from a set of numeric function results.
select min(length(s)) from t1;
-- Can also be used in combination with DISTINCT and/or GROUP BY.
-- Return more than one result.
select month, year, min(purchase_price) from store_stats group by month, year;
-- Filter the input to eliminate duplicates before performing the calculation.
select min(distinct x) from t1;

An aggregate function that returns an approximate value similar to the result of COUNT(DISTINCT col), the "number of distinct values". It is much faster than the combination of COUNT and DISTINCT, and uses a constant amount of memory and thus is less memory-intensive for columns with high cardinality.

This is the mechanism used internally by the COMPUTE STATS statement for computing the number of distinct values in a column.

Usage notes:

Because this number is an estimate, it might not reflect the precise number of different values in the column, especially if the cardinality is very low or very high. If the estimated number is higher than the number of rows in the table, Impala adjusts the value internally during query planning.

Return type: BIGINT

An aggregate function that returns the sum of a set of numbers. Its single argument can be numeric column, or the numeric result of a function or expression applied to the column value. Rows with a NULL value for the specified column are ignored. If the table is empty, or all the values supplied to MIN are NULL, SUM returns NULL.

When the query contains a GROUP BY clause, returns one value for each combination of grouping values.

Return type: BIGINT for integer arguments, DOUBLE for floating-point arguments

Examples:

-- Total all the values for this column in the table.
select sum(c1) from t1;
-- Find the total for this column from a subset of the table.
select sum(c1) from t1 where month = 'January' and year = '2013';
-- Find the total from a set of numeric function results.
select sum(length(s)) from t1;
-- Often used with functions that return predefined values to compute a score.
select sum(case when grade = 'A' then 1.0 when grade = 'B' then 0.75 else 0) as class_honors from test_scores;
-- Can also be used in combination with DISTINCT and/or GROUP BY.
-- Return more than one result.
select month, year, sum(purchase_price) from store_stats group by month, year;
-- Filter the input to eliminate duplicates before performing the calculation.
select sum(distinct x) from t1;