Guruh talabasi Abdig’opporov javoxir Mysql 1-2-amaliy ishlar

emp_no INT UNSIGNED NOT NULL,
dept_no CHAR(4) NOT NULL,
from_date DATE NOT NULL,
to_date DATE NOT NULL,
INDEX (emp_no), -- Build INDEX on this non-unique-value column
INDEX (dept_no), -- Build INDEX on this non-unique-value column
FOREIGN KEY (emp_no) REFERENCES employees (emp_no)
ON DELETE CASCADE ON UPDATE CASCADE,
FOREIGN KEY (dept_no) REFERENCES departments (dept_no)
ON DELETE CASCADE ON UPDATE CASCADE,
PRIMARY KEY (emp_no, dept_no) -- Index built automatically
);
mysql> DESCRIBE dept_emp;
+-----------+------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------+------------------+------+-----+---------+-------+
| emp_no | int(10) unsigned | NO | PRI | NULL | |
| dept_no | char(4) | NO | PRI | NULL | |
| from_date | date | NO | | NULL | |
| to_date | date | NO | | NULL | |
+-----------+------------------+------+-----+---------+-------+
mysql> SHOW INDEX FROM dept_emp \G
*************************** 1. row ***************************
Table: dept_emp
Non_unique: 0
Key_name: PRIMARY
Seq_in_index: 1
Column_name: emp_no
........
*************************** 2. row ***************************
Table: dept_emp
Non_unique: 0
Key_name: PRIMARY
Seq_in_index: 2
Column_name: dept_no
........
*************************** 3. row ***************************
Table: dept_emp
Non_unique: 1
Key_name: emp_no
Seq_in_index: 1
Column_name: emp_no
........
*************************** 4. row ***************************
Table: dept_emp
Non_unique: 1
Key_name: dept_no
Seq_in_index: 1
Column_name: dept_no
........
5. More SQL
5.1 Sub-Query
Results of one query can be used in another SQL statement. Subquery is useful if more than one tables are involved.