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III.12.3 Constraint naming standard

By Michael Bryzek

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Constraint naming standard is important for one reason: The SYS_* name oracle assigns to unnamed constraints is not very understandable. By correctly naming all contraints, we can quickly associate a particular constraint with our data model. This gives us two real advantages:

  • We can quickly identify and fix any errors.

  • We can reliabily modify or drop constraints

Why do we need a naming convention?

Oracle limits names, in general, to 30 characters, which is hardly enough for a human readable constraint name.

We propose the following naming convention for all constraints, with the following abbreviations taken from Oracle Docs at http://oradoc.photo.net/ora81/DOC/server.815/a67779/ch4e.htm#8953. Note that we shortened all of the constraint abbrevations to two characters to save room.

Constraint type Abbreviation
references (foreign key) fk
unique un
primary key pk
check ck
not null nn

<table name>_<column_name>_<constraint abbreviation>

In reality, this won't be possible because of the character limitation on names inside oracle. When the name is too long, we will follow these two steps in order:

  1. Abbreviate the table name with the table's initials (e.g. users -> u and users_contact -> uc).

  2. Truncate the column name until it fits.

If the constraint name is still too long, you should consider rewriting your entire data model :)

Notes:

  • If you have to abbreviate the table name for one of the constraints, abbreviate it for all the constraints

  • If you are defining a multi column constraint, try to truncate the two column names evenly 

create table example_topics (
       topic_id    integer
		   constraint example_topics_topic_id_pk
		   primary key
);

create table constraint_naming_example (
       example_id		      integer
				      constraint cne_example_id_pk
				      primary key,
       one_line_description	      varchar(100)
				      constraint cne_one_line_desc_nn
				      not null,
       body			      clob,
       up_to_date_p		      char(1) default('t')
				      constraint cne_up_to_date_p_check
				      check(up_to_date_p in ('t','f')),
       topic_id			      constraint cne_topic_id_nn not null
				      constraint cne_topic_id_fk references example_topics,
       -- Define table level constraint
       constraint cne_example_id_one_line_unq unique(example_id, one_line_description)
);

Naming primary keys might not have any obvious advantages. However, here's an example where naming the primary key really helps (and this is by no means a rare case! 

SQL> set autotrace traceonly explain;


SQL> select * from constraint_naming_example, example_topics
where constraint_naming_example.topic_id = example_topics.topic_id;

Execution Plan
----------------------------------------------------------
   0	  SELECT STATEMENT Optimizer=CHOOSE
   1	0   NESTED LOOPS
   2	1     TABLE ACCESS (FULL) OF 'CONSTRAINT_NAMING_EXAMPLE'
   3	1     INDEX (UNIQUE SCAN) OF 'EXAMPLE_TOPICS_TOPIC_ID_PK' (UNI
	  QUE)

Isn't it nice to see "EXAMPLE_TOPICS_TOPIC_ID_PK" in the trace and know exactly which table oracle is using at each step?

People disagree on whether or not we should be naming not null constraints. So, if you want to name them, please do so and follow the above naming standard. But, naming not null constraints is not a requirement.

About Naming the not null constraints

Though naming "not null" constraints doesn't help immeditately in error debugging (e.g. the error will say something like "Cannot insert null value into column"), we recommend naming not null constraints to be consistent in our naming of all constraints.