Αποτελέσματα Αναζήτησης
To create a PRIMARY KEY constraint on the "ID" column when the table is already created, use the following SQL: MySQL / SQL Server / Oracle / MS Access: ALTER TABLE Persons. ADD PRIMARY KEY (ID);
In this tutorial, you have learned how to use Oracle PRIMARY KEY constraint to create, add, disable, enable, and drop a primary key of a table.
13 Ιουλ 2012 · ALTER TABLE table_name ADD CONSTRAINT pk_table_name PRIMARY KEY( new_pk_column ) If you want to generate the key automatically, you'd need to add a trigger. CREATE TRIGGER trigger_name BEFORE INSERT ON table_name FOR EACH ROW BEGIN :new.new_pk_column := sequence_name.nextval; END; If you are on an older version of Oracle, the syntax is a bit ...
28 Αυγ 2015 · If we want to make our table to have primary key set {old_key, new_key}, then the following statement can be used: ALTER TABLE my_test_table DROP PRIMARY KEY, -- You have to add this ADD PRIMARY KEY( old_key, -- Re-mention the old key new_key -- And mention also the new one );
To create a new table with a column defined as the primary key, you can use the keyword PRIMARY KEY at the end of the definition of that column. In our example, we create the table product using a CREATE TABLE clause, with the names of the columns and their respective data types in parentheses.
Creating table with primary key. Generally, you define the primary key when creating the table. If the primary key consists of one column, you can use the PRIMARY KEY constraint as a column or table constraint. If the primary key consists of two or more columns, you must use the PRIMARY KEY constraint as the table constraint.
CREATE TABLE table_name( column1 datatype, column2 datatype, column3 datatype, ..., PRIMARY KEY(column1, column2) ); In this syntax, you list the primary key columns inside parentheses, separated by commas, followed by the PRIMARY KEY keywords.
