Set similar values for columns in MySQL table?-Mysql Tutorial-php.cn

Set similar values for columns in MySQL table?

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Release： 2023-09-02 09:17:08

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为 MySQL 表中的列设置类似的值？

You can set values for all records in a column with the help of the update command.

If you want to set NULL values for all records in a column, the syntax is as follows -

update yourTableName set yourColumnName = NULL;

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Or, if you want to use an empty string, the syntax is as follows -

update yourTableName set yourColumnName = &rsquo;&rsquo;;

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To understand the above concept, let us create a table. Query to create table.

mysql> create table StudentDemo
   &minus;> (
   &minus;> Studentid int,
   &minus;> StudentName varchar(100),
   &minus;> Age int
   &minus;> );
Query OK, 0 rows affected (0.64 sec)

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The following is the table into which records are inserted-

mysql> insert into StudentDemo values(1,&#39;Johnson&#39;,23);
Query OK, 1 row affected (0.18 sec)

mysql> insert into StudentDemo values(2,&#39;Carol&#39;,24);
Query OK, 1 row affected (0.16 sec)

mysql> insert into StudentDemo values(3,&#39;David&#39;,20);
Query OK, 1 row affected (0.18 sec)

mysql> insert into StudentDemo values(4,&#39;Bob&#39;,21);
Query OK, 1 row affected (0.19 sec)

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Use the select statement to display all records in the table-

mysql> select *from StudentDemo;

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The following is the output-

+-----------+-------------+------+
| Studentid | StudentName | Age |
+-----------+-------------+------+
|         1 | Johnson     | 23   |
|         2 | Carol       | 24   |
|         3 | David       | 20   |
|         4 | Bob         | 21   |
+-----------+-------------+------+
4 rows in set (0.00 sec)

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The following The query sets the column value to NULL for all records in a specific column. The query is as follows -

mysql> update StudentDemo set Age=NULL;
Query OK, 4 rows affected (0.14 sec)
Rows matched: 4 Changed: 4 Warnings: 0

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Now let us check it -

mysql> select *from StudentDemo;

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The following output shows that we have successfully updated the "Age" column to NULL -

+-----------+-------------+------+
| Studentid | StudentName | Age |
+-----------+-------------+------+
|         1 | Johnson     | NULL |
|         2 | Carol       | NULL |
|         3 | David       | NULL |
|         4 | Bob         | NULL |
+-----------+-------------+------+
4 rows in set (0.00 sec)

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