constraint unique sql
ALTER TABLE table_name ADD CONSTRAINT cst_name UNIQUE (col_name);
ALTER TABLE table_name ADD CONSTRAINT cst_name UNIQUE (col1, col2); -- Multiple
ALTER TABLE table_name ADD col_name NUMBER UNIQUE; -- New fieldconstraint unique sql
ALTER TABLE table_name ADD CONSTRAINT cst_name UNIQUE (col_name);
ALTER TABLE table_name ADD CONSTRAINT cst_name UNIQUE (col1, col2); -- Multiple
ALTER TABLE table_name ADD col_name NUMBER UNIQUE; -- New fieldunique key in sql
Unique Key:
Only unique value and also can contain NULLUnique Key in sql
CREATE TABLE Students ( /* Create table with a single field as unique */
ID INT NOT NULL UNIQUE
Name VARCHAR(255)
);
CREATE TABLE Students ( /* Create table with multiple fields as unique */
ID INT NOT NULL
LastName VARCHAR(255)
FirstName VARCHAR(255) NOT NULL
CONSTRAINT PK_Student
UNIQUE (ID, FirstName)
);
ALTER TABLE Students /* Set a column as unique */
ADD UNIQUE (ID);
ALTER TABLE Students /* Set multiple columns as unique */
ADD CONSTRAINT PK_Student /* Naming a unique constraint */
UNIQUE (ID, FirstName);Copyright © 2021 Codeinu
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