Archive for the ‘Oracle’ Category

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Oracle Constraints

Wednesday, February 14th, 2007

Constraints are used to keep accurate data. In oracle you can apply these policies to a column or table. There are five different types of constraints:

Constraint Abbreviation Description
PRIMARY KEY _pk This is a unique field that is not allowed to have null values.
FOREIGN KEY _fk This constraint is placed in the “many” table. The data that’s entered in this field must have a value in the parent table.
UNIQUE _uk All data that is stored in a column with a UNIQUE constraint on it will not have two of the same values. This constraint is a bit different from a PRIMARY KEY where the PRIMARY KEY does not allow NULLs, a UNIQUE constraint does allow NULLs.
CHECK _ck This constraint ensures that a specified condition is true before any data is added to the table.
NOT NULL _nn This makes sure that there is a value going into the table.

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Creating and Managing Tables in Oracle 10g

Wednesday, February 14th, 2007

When creating tables in Oracle we have to follow some rules in order to successfully create a table:

  • Table names and columns can be up to 30 characters long.
  • Names of tables and columns cannot have any blank spaces.
  • Numbers, underscores, and number signs are allowed in the table and column name.
  • Each table that a user owns must have a unique name and each column in that table must have a unique column name.
  • You can’t use reserved keywords as a table or column name.

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