Standard SQL is a beautiful language. Vendor specific implementations, however, have their warts. In Oracle, for example, it's not possible to update any columns in a MERGE statement, which have been referenced by the ON clause. For example: CREATE TABLE person ( id NUMBER(18) NOT NULL PRIMARY KEY, user_name VARCHAR2(50) NOT NULL UNIQUE, score NUMBER(18) … Continue reading How to Work Around ORA-38104: Columns referenced in the ON Clause cannot be updated
Tag: UNIQUE constraint
How Adding a UNIQUE Constraint on a OneToOne Relationship Helps Performance
A lot of people use SQL constraints mainly to enforce data integrity, and that's already a very good thing. A UNIQUE constraint, for instance, makes sure that there is at most one instance of any possible value (or tuple, in the case of a composite constraint) in a table. For instance: CREATE TABLE x ( … Continue reading How Adding a UNIQUE Constraint on a OneToOne Relationship Helps Performance