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Software Engineering vocabulary · Databases and Persistence

Constraint

Meaning in software engineering, with examples

/kənˈstreɪnt/nounCore term

In software engineering, constraint means: A rule set on a table or column that the database enforces automatically, rejecting any data that would break it.

In Turkish: kısıt, kısıtlama

How it is used

The main kinds are PRIMARY KEY, FOREIGN KEY, UNIQUE, NOT NULL, CHECK and DEFAULT (some books do not count DEFAULT as a real constraint). Data that breaks one causes a 'constraint violation' error. You add, drop, name and sometimes temporarily disable constraints during large data loads.

Example sentences

  1. A CHECK constraint makes sure the discount is between 0 and 100.

  2. Give every constraint a clear name so error messages are easy to understand.

Common collocations

  • add a constraint
  • constraint violation
  • CHECK constraint
  • drop a constraint
  • enforce a constraint
  • primary keyA column, or a set of columns, whose value uniquely identifies each row in a table. It cannot be empty and no two rows can share it.
  • foreign keyA column in one table that points to the primary key of another table, linking the two and stopping you from storing references to rows that do not exist.
  • unique constraintA rule that stops two rows from having the same value in a column or combination of columns, for example two users with the same email address.
  • NULLA special marker meaning that a value is missing or unknown. It is not the same as zero or an empty string.
  • referential integrityThe rule that every reference between tables must point to a row that really exists, so there are no orders for missing customers.

This word in other fields

The same English word can have a different meaning in another field:

More terms: Databases and Persistence

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