If there is already a constraint of the same name a useful error is returned. in this case would prefer to just check for the existing constraint. Note that means that for the same schema and the same data, the same query may work or fail depending on the execution plan. You'll have to make the constraint DEFERRABLE or DEFERRABLE INITIALLY DEFERRED, which delays verification of the constraint until the end of the transaction or up to the point where a statement SET CONSTRAINTS. TABLEPLUS CHECK UNIQUE CONSTRAINT POSTGRESQL VERIFICATION IMMEDIATE is executed.įor COPY, it seems, that (even IMMEDIATE) constraints are tested after all data are COPYied.CREATE TABLE discount (cust_ID INT Unique, product_name VARCHAR (100) NOT NULL, product_price varchar (10) NOT NULL, product_discount NUMERIC).In the above example, we have created a unique constraint on the cust_id column in the discount table.On cust_id column, Btree index was automatically created while using a unique constraint on cust_id column.While creating a unique constraint on the column every time of data insertion, it will check duplicate records from all rows of a table.If we are updating the value on the column row and which was already present in the table, it will issue an error.Here is one way of adding a unique constraint to our users table for the email column: alter table users add unique (email). If we are inserting a value that was present in a table, it will issue an error like “duplicate key violates unique constraint”.
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