not null

Constraint (Constraint): A restriction on the column properties, fields of the created table. such as: Not Null/unique/primary key/foreign Key/checkScope of Action:① column-level constraints only work on one column② table-level constraints can

Believe that a lot of people who have been using MySQL for a long time, the concept of these two field properties is not very clear, the general will have the following questions: My field type is not NULL, why can I insert a null value

Constraint (Constraint): A restriction on the column properties, fields of the created table.such as: Not Null/unique/primary key/foreign Key/checkScope of Action:① column-level constraints only work on a single column② table-level constraints can

Not NULL | Null: Specifies whether the column is allowed to be empty. If NULL is not specified and NOT NULL is specified, the column is considered to specify NULL In MySQL, Sets a null value for a not NULL field. It's not going to go wrong, MySQL

Original: http://blog.csdn.net/fwkjdaghappy1/article/details/7703974/Believe that a lot of people who have been using MySQL for a long time, the concept of these two field properties is not very clear, the general will have the following questions:1,

2, NOT NULL non-null constraint　　Used to ensure that the value at the top of the column is not empty, and that the field defaults to NULL if you do not specify whether it can be empty when you create the table.--This is the table created by the

Mysql explores not null constraints and null values, and mysqlnull Yesterday, a front-end developer suddenly asked me a basic question: "My table columns have the not null constraint. Why can I insert null values? What's more strange is that you can

Is not null and! in SQL! = NULL difference, sqlnull These two methods are often used: is not null and! = NULL. We often encounter database conditions! = NULL, but the returned result is a NULL set. In fact, the difference is not fully understood. By

Add a new column to a table with records and specify not null to report a ORA-01758. What should I do? 1. Specify the default value for the newly added column. 2. Clear the records in the table and add new columns. The experiment is as follows:

Not NULL | Null: Specifies whether the column is allowed to be empty. If neither NULL nor NULL is specified, the column is considered to have null specified In MySQL, Set a null value for a NOT null field, It's not going to go wrong, MySQL

Believe that a lot of people who have been using MySQL for a long time, the concept of these two field properties is not very clear, the general will have the following questions:1, my field type is not NULL, why I can insert null value2, the

1.SQL not NULL constraintThe NOT NULL constraint enforces that the column does not accept null values.A NOT NULL constraint forces a field to always contain a value. This means that if you do not add a value to the field, you cannot insert a new

Today encountered a problem, itself in the local Data execution insert SQL nothing wrong, but on the test environment on the error! Find a long time to find out about MySQL configuration. View Local DatabaseSELECT @ @sql_modeis empty, the test

Believe that a lot of people who have been using MySQL for a long time, the concept of these two field properties is not very clear, the general will have the following questions:1, my field type is not NULL, why I can insert null value2, the

These two types of writing are often encountered: are not NULL and!=null. It is also often encountered that the database has!=null data, but returns to an empty collection. In fact, it is because the difference between the two uses is not understood.

It is slow to add a NOT null field before 11g. It was soon after 11g. Let's do a test first and then explore the principles.Sql> select * from V$version;BANNER----------------------------------------------------------------Oracle Database 10g

Explicit_defaults_for_timestampMySQL5.6 Version IntroductionExplicit_defaults_for_timestampto control the timestamp NULL handling of Values timestamp not NULL insert null value, no error, no warning if the my.cnf Zhong

Believe that a lot of people who have been using MySQL for a long time, the concept of these two field properties is not very clear, the general will have the following questions:1, my field type is not NULL, why I can insert null value2, the

Servlet. Service () for servlet default threw exceptionOrg. hibernate. propertyvalueexception: Not-null property references a null or transient value: entity. favoritebook. UserAt org. hibernate. Engine. nullability. checknullability (nullability.

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