COUNT

Returns the count of numeric values, or only the distinct values.

Syntax

-- As an aggregate
COUNT( { [ DISTINCT ] expr | * } ) --> INT

-- As a window function
COUNT ( { [ DISTINCT ] expr | * } ) OVER (
         [ PARTITION BY value_expression [, ...] ]
         [ ORDER BY value_expression [ ASC | DESC ] [ NULLS { FIRST | LAST } ] [, ...] ]
         [ frame_clause ]
      )

Arguments

Parameter Description
expr Any value expression
* Specifies that COUNT should count all rows. It does not use information about any particular column, and preserves duplicate rows and NULL values.
DISTINCT Specifies that the operation should operate only on unique values

Returns

Return type is dependant on the argument.

  • Count returns INT for all types except BIGINT.
  • For BIGINT, the return type is BIGINT.

Notes

  • NULL values are not ignored by COUNT
  • When all rows contain NULL values, the function returns NULL.
  • COUNT can very quickly overflow on large data sets. If the count is over 231, up-cast to a larger type like BIGINT: COUNT(expr :: BIGINT)

Examples

For these examples, assume a table named nba, with the following structure:

CREATE TABLE nba
(
   "Name" varchar(40),
   "Team" varchar(40),
   "Number" tinyint,
   "Position" varchar(2),
   "Age" tinyint,
   "Height" varchar(4),
   "Weight" real,
   "College" varchar(40),
   "Salary" float
 );

Here’s a peek at the table contents (Download nba.csv):

nba.csv
Name Team Number Position Age Height Weight College Salary
Avery Bradley Boston Celtics 0.0 PG 25.0 6-2 180.0 Texas 7730337.0
Jae Crowder Boston Celtics 99.0 SF 25.0 6-6 235.0 Marquette 6796117.0
John Holland Boston Celtics 30.0 SG 27.0 6-5 205.0 Boston University  
R.J. Hunter Boston Celtics 28.0 SG 22.0 6-5 185.0 Georgia State 1148640.0
Jonas Jerebko Boston Celtics 8.0 PF 29.0 6-10 231.0   5000000.0
Amir Johnson Boston Celtics 90.0 PF 29.0 6-9 240.0   12000000.0
Jordan Mickey Boston Celtics 55.0 PF 21.0 6-8 235.0 LSU 1170960.0
Kelly Olynyk Boston Celtics 41.0 C 25.0 7-0 238.0 Gonzaga 2165160.0
Terry Rozier Boston Celtics 12.0 PG 22.0 6-2 190.0 Louisville 1824360.0

Count rows in a table

t=> SELECT COUNT(*) FROM nba;
count
-----
457

Count distinct values in a table

These two forms are equivalent:

t=> SELECT COUNT(distinct "Age") FROM nba;
count
-----
22

t=> SELECT COUNT(*) FROM (SELECT "Age" FROM nba GROUP BY 1);
count
-----
22

Combine COUNT with other aggregates

t=> SELECT "Age", AVG("Salary") as "Average salary", COUNT(*) as "Number of players" FROM nba GROUP BY 1;
Age | Average salary | Number of players
----+----------------+------------------
 19 |        1930440 |                 2
 20 |        2725790 |                19
 21 |        2067379 |                19
 22 |        2357963 |                26
 23 |        2034746 |                41
 24 |        3785300 |                47
 25 |        3930867 |                45
 26 |        6866566 |                36
 27 |        6676741 |                41
 28 |        5110188 |                31
 29 |        6224177 |                28
 30 |        7061858 |                31
 31 |        8511396 |                22
 32 |        7716958 |                13
 33 |        3930739 |                14
 34 |        7606030 |                10
 35 |        3461739 |                 9
 36 |        2238119 |                10
 37 |       12777778 |                 4
 38 |        1840041 |                 4
 39 |        2517872 |                 2
 40 |        4666916 |                 3