Sams Teach Yourself SQL in 21 Days, Fourth Edition

Using Aggregate Functions to Summarize Data

These functions are also referred to as group functions. They return a value based on the values in a column. (After all, you wouldn't ask for the average of a single field.) The examples in this section use the table TEAMSTATS:

SQL> SELECT * FROM TEAMSTATS;

NAME      POS  AB HITS WALKS SINGLES DOUBLES TRIPLES HR SO
------- ----- --- ---- ----  -----    ------ ------ --- ---
JONES      1B 145  45  34    31       8       1     5   10
DONKNOW    3B 175  65  23    50       10      1     4   15
WORLEY     LF 157  49  15    35        8      3     3   16
DAVID      OF 187  70  24    48        4      0     17  42
HAMHOCKER  3B  50  12  10    10        2      0      0  13
CASEY      DH   1   0   0     0        0      0      0   1

6 rows selected.

COUNT

The function COUNT returns the number of rows that satisfy the condition in the WHERE clause. Say you wanted to know how many ball ...