"SQL Cookbook" Learning notes

First, retrieve data:

1. Find rows that meet multiple criteria:

SELECT
*
From
Emp
WHERE
DEPTNO = 10
OR Comm is not NULL
OR Sal <= 2000
and DEPTNO = 20;

It returns all employees in the department 10 + all employees who receive a commission + 20 of employees with a salary not exceeding $2000.

SELECT
*
From
Emp
WHERE
(
Deptno = 10
OR Comm is not NULL
OR Sal <= 2000
)
and DEPTNO = 20;

It only returns to the eligible employees in Department 20

2. Refer to the alias column in the WHERE clause:

SELECT
*
From
(
SELECT
Sal as salary,
Comm As Commision
From
Emp
) x
WHERE
Salary < 5000;

3. Connection column values:

SELECT
ename | | ' WORKS as A ' | | JOB
From
Emp
WHERE
Deptno = 10;

4.

"SQL Cookbook" Learning notes