Taarifa ya Jedwali la SQL

Taarifa ya ALTER TABLE katika SQL hutumiwa kuongeza, kurekebisha au kufuta safu wima za meza.

Tunaweza pia kutumia taarifa ya ALTER TABLE kuongeza au kuacha vizuizi anuwai vya meza.

SQL ALTER TABLE - Ongeza safu mpya

Kuongeza safu mpya kwenye meza iliyopo tunatumia syntax:

ALTER TABLE table_name ADD column_name datatype;

Mfano

Nambari ifuatayo inaongeza safu wima ya 'Start_Date' kwenye jedwali la 'Wafanyikazi':

ALTER TABLE Employees ADD Start_Date date;

SQL ALTER TABLE - Ondoa safu

Kuondoa safu kutoka kwenye meza iliyopo tunatumia syntax:

ALTER TABLE table_name DROP COLUMN column_name;

Mfano

Nambari ifuatayo huondoa safu ya 'Start_Date' kutoka kwenye jedwali la 'Wafanyikazi':

ALTER TABLE Employees DROP COLUMN Start_Date;

SQL ALTER TABLE - Rekebisha safu wima

Tunaweza kutumia ALTER TABLE taarifa ya kurekebisha safu ya data ya safu wima kwa kutumia sintaksia:

ALTER TABLE table_name MODIFY column_name datatype;

Mfano

Nambari ifuatayo inabadilisha hifadhidata ya safu ya 'Start_Date' kutoka date kwa year:

ALTER TABLE Employees MODIFY Start_Date year;

SQL ALTER TABLE - Hifadhidata ya Maonyesho

Tuseme tuna meza inayoitwa 'Wafanyakazi' na safu zifuatazo:

+------------+-----------+----------+ | EmployeeID | FirstName | LastName | +------------+-----------+----------+ | 1

| Mark
| Otto
| | 2

| Jacob
| Thornton | | 3

| Su
| Bird
| | 4

| Sam
| Burger | +------------+-----------+----------+

Ongeza safu

Sasa tunataka kupanua jedwali la 'Wafanyikazi' na kuongeza safu mpya inayoitwa 'Start_Date'

ALTER TABLE Employees ADD Start_Date date;

Pato:

+------------+-----------+----------+------------+ | EmployeeID | FirstName | LastName | Start_Date | +------------+-----------+----------+------------+ | 1

| Mark
| Otto
|

| | 2

| Jacob
| Thornton |

| | 3

| Su
| Bird
|

| | 4

| Sam
| Burger |

| +------------+-----------+----------+------------+

Rekebisha safu wima

Ifuatayo tunataka kurekebisha safu ya data ya safu ya 'Start_Date' kutoka date kwa year:

ALTER TABLE Employees MODIFY Start_Date year;

Futa Safu wima

Tunataka kufuta safu ya 'Start_Date' kutoka kwenye jedwali la 'Wafanyikazi'. Tunatumia:

ALTER TABLE Employees DROP COLUMN Start_Date;

Pato:

+------------+-----------+----------+ | EmployeeID | FirstName | LastName | +------------+-----------+----------+ | 1

| Mark
| Otto
| | 2

| Jacob
| Thornton | | 3

| Su
| Bird
| | 4

| Sam
| Burger | +------------+-----------+----------+