what is MySql signed / unsigned option?

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When to use signed / unsigned option in MySql.

Mysql Says: 

All integer types can have an optional (nonstandard) attribute UNSIGNED. Unsigned type can be used to permit only nonnegative numbers in a column or when you need a larger upper numeric range for the column. For example, if an INT column is UNSIGNED, the size of the column’s range is the same but its endpoints shift from -2147483648 and 2147483647 up to 0 and 4294967295.

When to use UNSIGNED data type?

If your field will never stores negative values, then its best to use UNSIGNED, that will give you faster index and more range.

When to use  SIGNED data type?

If you need to store negative then use signed, but remember your number range is half now.

 

Note: Common mistake people do is to store primary number ( auto -increment ) as as signed. Which mean you are already reducing your number range even you will never use negative number as your primary key.

MySQL supports the SQL standard integer types INTEGER (or INT) and SMALLINT. As an extension to the standard, MySQL also supports the integer typesTINYINT, MEDIUMINT, and BIGINT. The following table shows the required storage and range for each integer type.

Type Storage Minimum Value Maximum Value
(Bytes) (Signed/Unsigned) (Signed/Unsigned)
TINYINT 1 -128 127
0 255
SMALLINT 2 -32768 32767
0 65535
MEDIUMINT 3 -8388608 8388607
0 16777215
INT 4 -2147483648 2147483647
0 4294967295
BIGINT 8 -9223372036854775808 9223372036854775807
0 18446744073709551615
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MySQL naming / coding conventions: tips on mySQL database

MySQL_Workbench_Visual_Design_Windows

MySQL database naming conventions

There are coding standards on each programming language but in terms of MySQL I haven’t found any universal coding practice that everyone follows so i looked into different open source framework and popular PHP based software and found some generally applied standards on naming so I am trying to summaries it in this article.

Properly design MySQL with proper naming conventions will help to write SQL query faster, helps to remove confusions and conflicts both on queries and programming language.

MySQL Name conventions general rules:

  • Use lowercase: Will help on speed typing, avoid mistakes dues to case sensitivity e.t.c
  • No space – use underscore instead
  • No numbers in name only alpha English characters
  • Valid understandable names like  blog, ecommerce e.t.c but not like project, james, e.t.c
  • Name should be self explanatory
  • Names should not be more than 64 characters.
  • Avoid prefix

MySQL Database name convention:

Follow all the rules on general rules above.

  • Name can be both singular and plural but database represent one database so it should be singular if possible.
  • Avoid prefix if possible.

 

MySQL Table name:

  • Lower case table name: Mysql is usually hosted in Linux server which is case sensitive so for best practice table name should be all lower case. Many PHP or other programming framework auto detect or auto generate class based on table names and most of them expect lower table name.
  • Table name is Singular:
    We think table holds so may things like user table holds many users in the table, so name should be plural but table is a single entity as Model is only one so its odd to have plural table name.  So name your table like user, invoice, comment.
  • Prefix in table name: I have seen many times that table name has prefix usually db name or project name. Some time it is necessary to have prefix as in hosting envirnment we have many tables in one db to overcome limitation of db by hosting providers. But try to aviod them. Name should be small and meaningful rather than long menaning less names. If we cant avoid prefix then we can fix it by php classes.

 

Field Names:

Use all above cases i.e lowercase, no space, no numbers, and avoid prefix.

  • Choose short and one or two words as possible.
  • Field names should be understand able eg: price, company_name, e.t.c
  • Primary column name: Primary key can be id, or table name _id. Its depends on your own choice but for me, I prefer id as its self explanatory.
  • Avoid using reserve word as field name: order, date, name are reserve word for database avoid using it. You can add prefix to these names to make it understandable like user_name, signup_date e.t.c
  • Avoid using column with same name as table name. This can cause confusion while writing query.
  • Do define foreign key on database schema.
  • Avoid abbreviated, concatenated, or acronym-based names
  • Foreign key column must have table name with their primary key, eg: blog_id represents foreign key id from table blog.
  • Avoid semantically – meaningful primary key names. A classic design mistake is creating a table with primary key that has actual meaning like ‘name’ as primary key. In this case if some one change his name then relationship with other table will be effected and name can be repetitive (not unique).

Summary:

Make your table naming convention understandable for both database designers and programmers. It should avoid anything that might cause confusion, issues on linking tables to one another. And finally it should be readable for programming language or framework that is implemented.