SELECT AVG(sal), MAX(sal),
MIN(sal), SUM(sal)
FROM emp
WHERE job LIKE 'SALES%';
SELECT MIN(hiredate), MAX(hiredate)FROM emp;
SELECT COUNT(*)FROM emp
WHERE deptno = 30;
(*是列名最好是主键没有重复)
否则
SELECT count(DISTINCT deptno) FROM dept;
SELECT AVG(sal) as 销售的平均工资,sum(sal) as 销售的总工资 from emp where job like 'sales%'```
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