mysql make column not null

); Mysql> insert into my_table (phone) VALUES (""); The two statements insert values into the phone column, but the first statement inserts a NULL value and the second statement inserts an empty string. The first one can be thought of as "the phone number is unknown", while the second one can mean "she has no phone number ". In SQL, the

the row to 0, sort the field first, and then the age sortMysql> Select *,age is null as Agenull from Test_user order by Agenull,age; +----+-----------+------+---------+ | ID | Username | Age | Agenull | +----+-----------+------+---------+ | 6 | User6 | 23 | 0 | | 1 | User1 | 28 | 0 | | 2 | User2 | 30 | 0 | | 3 | User3 | NULL | 1 | | 4 | User4 | NULL | 1 | | 5 |

Mysql basics: mysql column type -- string bitsCN.com Mysql basics: mysql column type-string · CHAR This is a synonym for CHAR (1. · [NATIONAL] VARCHAR (M) [BINARY] Variable-length string. M indicates the maximum

MySQL NULL value processing instance details, mysqlnull MySQL NULL value processing We already know that MySQL uses the SQL SELECT command and the WHERE clause to read data in the data table. However, when the provided query condition field is

data type is int), Date (its data type is timestamp). Now insert a record into this table, where a null null value is inserted into the Date field. But when we query, the result is the current time that the record was inserted. What is this all about? In fact, this is a trap that is often encountered when executing SQL statements in a MySQL database:

columns containing null according to your own wishes, you can perform the preceding operations. [MySQL ]:MySQL is the same as sqlserver, and null is the minimum by default. The solution is the same as that of sqlserver. Note:1. When a null

, the Generated Column type is not specified. The default value is Virtual Column. In addition:Stored Generated Column has poor performance.If Stored Generated Golumn is required, it is more appropriate to create an index on the Generated Column. For details, see section 4th. In summary, generally, Virtual Generated

From: http://lz12366.iteye.com/blog/673290 The concept of null value is a common cause of confusion among SQL beginners. They often think that null is the same as an empty string. No! For example, the following statements are completely different: Mysql> insert into my_table (phone) values (null );

SQL statements in a MySQL database: Null values are not necessarily empty. When the operation, obviously inserted is a null value of data, but the last query is not a null value. In a MySQL database, NULL is a special type of

We have seen the SQL SELECT command using the WHERE clause to fetch data from the MySQL table. However, when we try to give the condition to compare the value of the field or column to NULL, it does not work correctly. To handle this situation, MySQL provides three major operators is

Usage of the is null statement in the mysql database Note that in mysql, 0 or null means false while other values mean true. The default true value of Boolean operations is 1. The special processing of null is in the previous chapter. To determine which animal is no longer a

Usage of the is null statement in the mysql database Note that in mysql, 0 or null means false while other values mean true. The default true value of Boolean operations is 1. The special processing of null is in the previous chapter. To determine which animal is no longer a

See: http://blog.yemou.net/article/query/info/tytfjhfascvhzxcyt338Many tables contain nullable (NULL) columns, even if the application well does not need to save NULL, because nullable is the default property of the column. It is generally preferable to specify column NOT NULL