VG和SUM函數(shù) 可以對數(shù)值型數(shù)據(jù)使用AVG 和 SUM 函數(shù)。
SELECT AVG(salary), MAX(salary),MIN(salary), SUM(salary) FROM employees WHERE job_id LIKE '%REP%'; 1.2 MIN和MAX函數(shù) 可以對任意數(shù)據(jù)類型的數(shù)據(jù)使用 MIN 和 MAX 函數(shù)。
SELECT MIN(hire_date), MAX(hire_date) FROM employees; 1.3 COUNT函數(shù) COUNT(*)返回表中記錄總數(shù)，適用于任意數(shù)據(jù)類型。 SELECT COUNT(*) FROM employees WHERE department_id = 50; COUNT(expr) 返回expr不為空的記錄總數(shù)。 SELECT COUNT(commission_pct) FROM employees WHERE department_id = 50; //忽略了Null值 計算表中有多少條記錄
