Add a Delete field to a table in MySQL

1 Increase of two fields:

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2. mysql> Create table id_name (id int,name varchar (20));
4. Query OK, 0 rows affected (0.13 sec)
10. mysql> alter table Id_name add age int,add address varchar (11);
12. Query OK, 0 rows affected (0.13 sec)
14. records:0 duplicates:0 warnings:0
18. mysql> desc id_name;
22. +---------+-------------+------+-----+---------+-------+  
24. | Field | Type | Null | Key | Default |  Extra |
26. +---------+-------------+------+-----+---------+-------+  
28. | ID | Int (11) |     YES | |       NULL |  |
30. | name | varchar (20) |     YES | |       NULL |  |
32. | Age | Int (11) |     YES | |       NULL |  |
34. | Address | varchar (11) |     YES | |       NULL |  |
36. +---------+-------------+------+-----+---------+-------+  
38. 4 rows in Set (0.00 sec)
42. 2. Delete two fields
44. mysql> alter table id_name drop column age,drop column address;
46. Query OK, 0 rows affected (0.14 sec)
48. records:0 duplicates:0 warnings:0
52. mysql> desc id_name;
54. +-------+-------------+------+-----+---------+-------+  
56. | Field | Type | Null | Key | Default |  Extra |
58. +-------+-------------+------+-----+---------+-------+  
60. | ID | Int (11) |     YES | |       NULL |  |
62. | name | varchar (20) |     YES | |       NULL |  |
64. +-------+-------------+------+-----+---------+-------+  
66. 2 rows in Set (0.00 sec)
70. 3. Insert
72. mysql> INSERT INTO id_name values (1,' QUSTDJX ');
74. Query OK, 1 row Affected (0.00 sec)
76. 4. See for yourself
78. mysql> alter table Id_name add age int,add address varchar (11);
80. Query OK, 1 row affected (0.07 sec)
82. Records:1 duplicates:0 warnings:0
86. Mysql> SELECT * from id_name;
88. +------+---------+------+---------+  
90. | ID |  Name | age | address |
92. +------+---------+------+---------+  
94. | 1 | QUSTDJX | NULL |  NULL |
96. +------+---------+------+---------+  
98. 1 row in Set (0.00 sec)
100. 5. Add fields and insert
102. mysql> INSERT INTO id_name values (2,' qust ', +,' Shandong ');
104. Query OK, 1 row Affected (0.00 sec)
108. Mysql> SELECT * from id_name;
110. +------+---------+------+---------+  
112. | ID |  Name | age | address |
114. +------+---------+------+---------+  
116. | 1 | QUSTDJX | NULL |  NULL |
118. | 2 |   Qust | 14 | Shandong |
120. +------+---------+------+---------+  
122. 2 rows in Set (0.00 sec)

1. Add a field
ALTER TABLE user add COLUMN new1 VARCHAR () DEFAULT NULL; Add a field, default is empty
ALTER TABLE user add COLUMN new2 VARCHAR (a) not NULL; Add a field that cannot be empty by default www.2cto.com

2. Delete a field
ALTER TABLE user DROP COLUMN new2; Delete a field

3. Modify a Field
ALTER TABLE user MODIFY New1 VARCHAR (10); Modify the type of a field

ALTER TABLE user change new1 new4 int; To modify the name of a field, be sure to re-specify the field's type

Add a Delete field to a table in MySQL