8 replies to this topic

[shogun89]

Sou um desenvolvedor que na maior parte do tempo utilizou o SQL Server nas suas aplicações.

Recentemente, comecei a utilizar o MySql, e me deparei com algumas situações curiosas, desde, campos "not null" permitindo nulos, até campos "char(5)", por exemplo, permitindo 3 caracteres...

 

Fico curioso com isso, pois não entendo a causa destas "falhas".

Como no SQL Server isto não é possível, me perco as vezes nas opções que tenho para uma simples query.

 

Um outro exemplo que me deparei hoje foi no caso do "group by".

No SQL Server, todos os campos selecionados devem constar no group by, já no MySql, não tive este problema.

 

[Danilomaru]

Ao especificar um campo com tipo char(5) ainda que insira um registro, por exemplo, somente com um caractere, ele irá gravar sem problemas (ex: 'a     '), ou seja, ainda que o campo seja char(200) e você gravar um registro com apenas um caractere, será ocupado todos os bytes 

 

not null

 

Muitos confundem isso ( not null != '' )

Faça um teste no console do mysql.

mysql> SELECT LENGTH('');
-> 0
mysql> SELECT LENGTH(null);
-> NULL

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