Mysql method to add int fields: use the ALTER TABLE statement, pass "ALTER TABLE table name ADD new field int (length);" or "ALTER TABLE table name ADD new field int (length) AFTER existing field ;" format to add.
#A complete field includes field name, data type and constraints. The syntax format for adding fields in MySQL is as follows:
ALTER TABLE <表名> ADD <新字段名><数据类型>[约束条件];
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The description of the syntax format is as follows:
is the name of the data table;
is the name of the field to be added;
is the data type that the field to be added can store data, which can be int, text;
[Constraints ] is optional and is used to constrain the added fields.
This syntax format adds a new field at the last position of the table (after the last column) by default.
Example
Create a new student data table in the test database. The SQL statements and running results are as follows:
mysql> USE test;
Database changed
mysql> CREATE TABLE student (
-> id INT(4),
-> name VARCHAR(20),
-> sex CHAR(1));
Query OK, 0 rows affected (0.09 sec)
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Use DESC to view the student table The structure, SQL statements and running results are as follows:
mysql> DESC student;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(4) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| sex | char(1) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.01 sec)
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Use the ALTER TABLE statement to add an INT type field age, the SQL statements and running results are as follows:
mysql> ALTER TABLE student ADD age INT(4);
Query OK, 0 rows affected (0.16 sec)
Records: 0 Duplicates: 0 Warnings: 0
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Use DESC to view the student table Structure, check whether the age field is added successfully. The SQL statement and running results are as follows:
mysql> DESC student;
+-------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id | int(4) | YES | | NULL | |
| name | varchar(20) | YES | | NULL | |
| sex | char(1) | YES | | NULL | |
| age | int(4) | YES | | NULL | |
+-------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
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As you can see from the running results, the age field has been added to the student table, and the field is at the last position of the table. The field was added successfully.
Sometimes you need to add a field in the middle, so what if you add a field in the middle?
You need to use the AFTER keyword at this time, the syntax format is as follows:
ALTER TABLE <表名> ADD <新字段名> <数据类型> [约束条件] AFTER <已经存在的字段名>;
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The function of AFTER is to add a new field after an existing field.
Note that you can only add a new field after an existing field, but not in front of it.
Example
Use the ALTER TABLE statement to add a field named stuno with data type INT in the student table. The stuno field is located after the name field. The SQL statement and running results are as follows:
As can be seen from the running results, the stuId field has been added to the student table, and the field is located behind the name field. The field was added successfully.
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