If you create a composite primary key, on (x, y, z), PostgreSQL implements this with the help of one UNIQUE multi-column btree index on (x, y, z). In addition, all three columns are NOT NULL (implicitly), which is the main difference between a PRIMARY KEY and a UNIQUE INDEX. Besides obvious restrictions on your data, … Read more
Since Table2 has a composite primary key (FileID, FileType), then any reference to it must also include both columns. ALTER TABLE dbo.Table1 ADD CONSTRAINT FK_Table1_Table2 FOREIGN KEY(FileID, FileType) REFERENCES Table2(FileID, FileType) Unless you have a unique constraint/index on the Table2.FileID field (but if so: why isn’t this the PK??), you cannot create a FK relationship … Read more
Let me answer step by step. 1. When do you need ` insertable = false, updatable = false`? Let’s look at the below mapping, public class Zip { @ManyToOne @JoinColumn(name = “country_code”, referencedColumnName = “iso_code”) private Country country = null @Column(name = “country_code”) private String countryCode; } Here we are referring to the same column … Read more
You shouldn’t really do this but insert in a new record instead and update it that way. But, if you really need to, you can do the following: Disable enforcing FK constraints temporarily (e.g. ALTER TABLE foo WITH NOCHECK CONSTRAINT ALL) Then update your PK Then update your FKs to match the PK change Finally … Read more
I personally prefer your 2nd approach (and would use it almost 100% of the time) – introduce a surrogate ID field. Why? makes life a lot easier for any tables referencing your table – the JOIN conditions are much simpler with just a single ID column (rather than 2, 3, or even more columns that … Read more
ALTER TABLE provider ADD PRIMARY KEY(person,place,thing); If a primary key already exists then you want to do this ALTER TABLE provider DROP PRIMARY KEY, ADD PRIMARY KEY(person, place, thing);
I’ve run into this problem a couple of times. You need to override some properties: protected $primaryKey = [‘user_id’, ‘stock_id’]; public $incrementing = false; and methods (credit): /** * Set the keys for a save update query. * * @param \Illuminate\Database\Eloquent\Builder $query * @return \Illuminate\Database\Eloquent\Builder */ protected function setKeysForSaveQuery(Builder $query) { $keys = $this->getKeyName(); if(!is_array($keys)){ … Read more
According to the documentation, it’s CREATE TABLE something ( column1, column2, column3, PRIMARY KEY (column1, column2) );
Just for clarification: a table can have at most one primary key. A primary key consists of one or more columns (from that table). If a primary key consists of two or more columns it is called a composite primary key. It is defined as follows: CREATE TABLE voting ( QuestionID NUMERIC, MemberID NUMERIC, PRIMARY … Read more
You can make an Embedded class, which contains your two keys, and then have a reference to that class as EmbeddedId in your Entity. You would need the @EmbeddedId and @Embeddable annotations. @Entity public class YourEntity { @EmbeddedId private MyKey myKey; @Column(name = “ColumnA”) private String columnA; /** Your getters and setters **/ } @Embeddable … Read more