Foreign key references multiple tables sheet

Delete the table from the database ALTER TABLE t ADD column; Add a new column to the table ALTER TABLE t DROP COLUMN c ; Drop column c from the table CREATE TABLE t1(c1 SERIAL PRIMARY KEY, c2 INT, FOREIGN KEY (c2) REFERENCES t2(c2)); Set c2 column as a foreign key CREATE TABLE t(c1 INT, c1 INT, UNIQUE(c2,c3)); Make the values in c1 and c2 ...

Sep 05, 2017 · I have recently needed to solve the task for my own purpose: to calculate the number of external records linked by a foreign key for each record in a table (File).The task was solved for the specific structure of the File table, but if necessary, the solution can be re wor ked to a universal one. Primary keys serve as unique identifiers for the records in a table, while foreign keys are used to link related tables together. When designing a set of database tables, it is important to specify which fields will be used for primary and foreign keys to clarify both in-table structure and inter-table relationships.

May 19, 2016 · How to create Foreign Key Constraint on Multiple Columns in SQL Server - SQL Server Tutorial Part 67 ... you need to create second table dbo.Orders and create foreign key constraint by using ... A FOREIGN KEY is a key used to link two tables together. A FOREIGN KEY is a field (or collection of fields) in one table that refers to the PRIMARY KEY in another table. The table containing the foreign key is called the child table, and the table containing the candidate key is called the referenced or parent table. So, the referencing table had two foreign key columns, and also it had a constraint to guarantee that exactly one table (not both, not neither) was referenced by a single row. Here's how it could look when applied to your tables: Setting foreign_key_checks to 0 can also be useful for ignoring foreign key constraints during LOAD DATA and ALTER TABLE operations. However, even if foreign_key_checks = 0 , MySQL does not permit the creation of a foreign key constraint where a column references a nonmatching column type. I need a simple stored procedure that create a foreign Key that refer to multiple primary keys in different tables. Ex: first table is the Student table which contains StuId and StuName. Sec table is the Non-Student table which contains NonStuId and NonStuName. I need SP that create third table contains . Id , ObjId_FK

The main purpose of FOREIGN KEY is, only those values will appear which are present in the primary key table. For each row in the referencing table( the table contains the FOREIGN KEY), the foreign key must match an existing primary key in the referenced table(the table contains the PRIMARY KEY). Dec 29, 2012 · I have four table, three of these are parent table and one of these is a child table. I want to create relation between parent tables and child table. Well I want to create 3 foreign key relation on the same child table column. The child key is the column or set of columns in the child table that are constrained by the foreign key constraint and which hold the REFERENCES clause. The foreign key constraint is satisfied if for each row in the child table either one or more of the child key columns are NULL, or there exists a row in the parent table for which each parent ...