The below figure shows the error message after inserting the same record, which was present in a table.If we are inserting a value that was present in a table, it will issue an error like “duplicate key violates unique constraint”.If we are updating the value on the column row and which was already present in the table, it will issue an error.While creating a unique constraint on the column every time of data insertion, it will check duplicate records from all rows of a table.On the cust_id column, the Btree index was automatically created while using a unique constraint on the cust_id column.In the above example, we have created a unique constraint on the cust_id column in the discount table.The below example shows that the index will automatically create on the cust_id column:Ĭode: CREATE TABLE discount (cust_ID INT Unique, product_name VARCHAR (100) NOT NULL, product_price varchar (10) NOT NULL, product_discount NUMERIC) While creating a unique constraint column or any group of the column, PostgreSQL will automatically create an index on that column. How UNIQUE Constraint works in PostgreSQL? Unique constraint: PostgreSQL unique constraint is straight that all the records in the table column are unique, duplicates are not allowed in it.Table name: We are creating a unique constraint on which column.The data type is most important while creating a table. Data type: Data type defines the type of data we have stored in the table.In this column, we are creating a unique constraint. Column 1 to column N: Column name used while creating a column in PostgreSQL.We can create a constraint on the table column. ![]() Create: Create a table by using a unique constraint in PostgreSQL.ALTER table table_name add column_name data_type UNIQUE īelow is a parameter description of the above syntax: It consists of the field called order_id.CREATE TABLE table_name (column_name1 data type, column_name2 data_type,Ĭolumn_nameNdata_type, UNIQUE (Column_name1, Column_name2)) Īccording to the syntax above, a collection of several columns were simultaneously used to construct a unique constraint. In this example, we've created a unique constraint on the existing order_details table called order_unique. ALTER TABLE order_detailsĪDD CONSTRAINT order_unique UNIQUE (order_id) Let's look at an example of how to add a unique constraint to an existing table in PostgreSQL using the ALTER TABLE statement. column_n The columns that make up the unique constraint. ![]() constraint_name The name of the unique constraint. This is the table that you wish to add a unique constraint to. column_n) table_name The name of the table to modify. The syntax for creating a unique constraint using an ALTER TABLE statement in PostgreSQL is: ALTER TABLE table_nameĪDD CONSTRAINT constraint_name UNIQUE (column1, column2. We could also create a unique constraint with more than one field as in the example below: CREATE TABLE order_detailsĬONSTRAINT order_date_unique UNIQUE (order_id, order_date)Ĭreate unique contraint - Using an ALTER TABLE statement It consists of only one field - the order_id field. In this example, we've created a unique constraint on the order_details table called order_unique. ![]() ( order_detail_id integer CONSTRAINT order_details_pk PRIMARY KEY,ĬONSTRAINT order_unique UNIQUE (order_id) Let's look at an example of how to create a unique constraint in PostgreSQL using the CREATE TABLE statement. uc_col_n The columns that make up the unique constraint. column1, column2 The columns that you wish to create in the table. ) table_name The name of the table that you wish to create. The syntax for creating a unique constraint using a CREATE TABLE statement in PostgreSQL is: CREATE TABLE table_nameĬONSTRAINT constraint_name UNIQUE (uc_col1, uc_col2. Create unique Contraint - Using a CREATE TABLE statement
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