The method of judging data duplication in MySQL

The practical application of my work. When collecting data, it is not necessary to repeat it after collection. At the same time, multiple instances are required to operate simultaneously to ensure the continuity of data acquisition. So summed up, made the following small experiment. The core code is as follows:

Table structure: only 3 fields

Id,name,password

SQL code

CREATE TABLE ' TT ' (  
  ' Id ' int (one) not null auto_increment,  
  ' name ' varchar (255) DEFAULT null,  
  ' password ' varcha R (255) default NULL,  
  PRIMARY KEY (' Id ')  
) engine=innodb default Charset=utf8;

SQL statement

1) Recommended

SQL code

Insert ignore into TT (Name,password) VALUES (' PHL ', ' 123 ')

2 is not recommended, because select will lock the Select table when insert

SQL code

INSERT INTO TT (name,password) Select ' PHL ', ' 123 ' to dual where NOT EXISTS (SELECT * from TT where name= ' PHL ' and password = ' 123 ')

The meaning of this SQL statement is that if the inserted data name= ' PHL ', password= ' 123 ' does not exist, the insertion is performed;

Add:

Method 1, there is no filter. It is because there is no joint master building of name and password;