Are foreign keys really necessary in a database design?
Foreign keys help enforce referential integrity at the data level. They also improve performance because they’re normally indexed by default.
foreign-keys
SqlAlchemy – Filtering by Relationship Attribute
Use method has() of relationship (more readable): patients = Patient.query.filter(Patient.mother.has(phenoscore=10)) or join (usually faster): patients = Patient.query.join(Patient.mother, aliased=True)\ .filter_by(phenoscore=10)
Ruby on Rails. How do I use the Active Record .build method in a :belongs to relationship?
Where it is documented: From the API documentation under the has_many association in “Module ActiveRecord::Associations::ClassMethods” collection.build(attributes = {}, …) Returns one or more new objects of the collection type that have been instantiated with attributes and linked to this object through a foreign key, but have not yet been saved. Note: This only works if … Read more
Add Foreign Key to existing table
To add a foreign key (grade_id) to an existing table (users), follow the following steps: ALTER TABLE users ADD grade_id SMALLINT UNSIGNED NOT NULL DEFAULT 0; ALTER TABLE users ADD CONSTRAINT fk_grade_id FOREIGN KEY (grade_id) REFERENCES grades(id);
Is it fine to have foreign key as primary key?
Foreign keys are almost always “Allow Duplicates,” which would make them unsuitable as Primary Keys. Instead, find a field that uniquely identifies each record in the table, or add a new field (either an auto-incrementing integer or a GUID) to act as the primary key. The only exception to this are tables with a one-to-one … Read more
Force drop mysql bypassing foreign key constraint
This might be useful to someone ending up here from a search. Make sure you’re trying to drop a table and not a view. SET foreign_key_checks = 0; — Drop tables drop table … — Drop views drop view … SET foreign_key_checks = 1; SET foreign_key_checks = 0 is to set foreign key checks to … Read more
PostgreSQL array of elements that each are a foreign key
It may soon be possible to do this: https://commitfest.postgresql.org/17/1252/ – Mark Rofail has been doing some excellent work on this patch! The patch will (once complete) allow CREATE TABLE PKTABLEFORARRAY ( ptest1 float8 PRIMARY KEY, ptest2 text ); CREATE TABLE FKTABLEFORARRAY ( ftest1 int[], FOREIGN KEY (EACH ELEMENT OF ftest1) REFERENCES PKTABLEFORARRAY, ftest2 int ); … Read more
When/Why to use Cascading in SQL Server?
Summary of what I’ve seen so far: Some people don’t like cascading at all. Cascade Delete Cascade Delete may make sense when the semantics of the relationship can involve an exclusive “is part of” description. For example, an OrderLine record is part of its parent order, and OrderLines will never be shared between multiple orders. … Read more
Does Foreign Key improve query performance?
Foreign Keys are a referential integrity tool, not a performance tool. At least in SQL Server, the creation of an FK does not create an associated index, and you should create indexes on all FK fields to improve look up times.
How to find foreign key dependencies in SQL Server?
The following query will help to get you started. It lists all Foreign Key Relationships within the current database. SELECT FK_Table = FK.TABLE_NAME, FK_Column = CU.COLUMN_NAME, PK_Table = PK.TABLE_NAME, PK_Column = PT.COLUMN_NAME, Constraint_Name = C.CONSTRAINT_NAME FROM INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS C INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS FK ON C.CONSTRAINT_NAME = FK.CONSTRAINT_NAME INNER JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS PK ON C.UNIQUE_CONSTRAINT_NAME = PK.CONSTRAINT_NAME INNER … Read more