mysql make column not null

This article describes how to understand and use the NULL value in MySQL, A friend may refer to the concept of NULL value as 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:

location of the error record can be easily found by searching for rows that contain null strings or corresponding numeric indexes of 0. SET Type The SET type is similar to the ENUM type but not the same. The SET type can obtain any number of values from a predefined SET. What is the same as the ENUM type is that any attempt to insert a non-predefined value in the SET Type field will make

Tags: MySQL data table column type and column constraintsMySQL data table when defining columns, you need to determine the data type of the column, as well as the related properties of the column or constraints, then the MySQL

The Mysql database provides two types of indexes. If they are not correctly set, the index utilization efficiency will be greatly reduced, but the problem is completely unknown. The copy code is as follows: CREATETABLEtest (idINTNOTNULL, last_nameCHAR (30) NOTNULL, first_nameCHAR (30) NOTNULL, PRIMARYKEY (id), INDEXname (l The Mysql database provides two types of indexes. If they are not correctly set, the

Mysql column-to-row and column-to-row Today, I saw a row-to-column and column-to-row problem when I went around Java. After reading this, I really don't know how to do it. I may usually use hibernate as the persistent layer, the SQL statement won't be written either. Hurry u

SELECT @ SQL _mode statement to query the current mode. The default value is null (no mode is set ).STRICT_TRANS_TABLESEnable strict mode for all storage engines. The invalid data value is denied. Detailed descriptions are provided later.· STRICT_TRANS_TABLESEnable strict mode for the transaction storage engine, or enable strict mode for the non-transaction storage engine. Detailed descriptions are provided later.Strictly control how

Create a table that uses the column index: CREATE TABLE Index_test1 (ID int NOT NULL auto_increment,first_name varchar (+) NOT NULL,last_name varchar (+) NOT NULL,Primary key (ID),Index Index_first (first_name),Index Index_last (last_name)) engine MyISAM charset UTF8;Create a table that uses multiple-

Tags: Table database capability effect int sha ble mysq typeThe MySQL database provides two types of indexes, and if not set correctly, the efficiency of the index is compromised but the problem is completely unknown. [C-sharp]View PlainCopy CREATE TABLE Test ( ID INT not NULL, Last_Name CHAR (+) not NULL, First_Name CHAR (+) not

MySQL database provides two types of indexes, if not set correctly, the efficiency of the index will be greatly compromised but the problem is completely unknown. Copy Code code as follows: CREATE TABLE Test ( ID INT not NULL, last_name CHAR () not NULL, first_name CHAR () not NULL, PRIMARY KEY (id), INDE

MySQL database provides two types of indexes, if not set correctly, the efficiency of the index will be greatly compromised but the problem is completely unknown. Copy Code code as follows: CREATE TABLE Test ( ID INT not NULL, Last_Name CHAR () not NULL, First_Name CHAR () not NULL, PRIMARY KEY

In MySQL, the processing of NULL fields, it is important to note that when there is null in the processing query condition, it is possible that the value you get is not desired because, in MySQL, the null value equals (=) is judged equal (=) or unequal (! =) will return FALS

Partition_names| REBUILD PARTITION Partition_names| REPAIR PARTITION Partition_namesSQL statement format for adding new columns to a table after a column in MySQLALTER table ' database name '. ' Table name ' ADD COLUMN ' ProcID ' VARCHAR (6) DEFAULT ' after ' ppidchanged ';In MySQL, if the table name, database name, column