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1. Only one primary key can be created for each table.2. Uniquely identifies each row in a table.3. Enforces uniqueness.4. Enforces NOT NULL constraints implicitly.

1. Only one primary key can be created for each table.2. Uniquely identifies each row in a table.3. Enforces uniqueness.4. Enforces NOT NULL constraints implicitly.

1. Either the table level or the column level CREATE TABLE employees ( employee_id NUMBER(6), last_name VARCHAR2(25) NOT NULL, email VARCHAR2(25), ... ... CONSTRAINT emp_email_uk UNIQUE(email)); ** The Oracle server enforces the UNIQUE constaint by implicityly creating a unique index on the unique key column or columns.

1. Either the table level or the column level CREATE TABLE employees ( employee_id NUMBER(6), last_name VARCHAR2(25) NOT NULL, email VARCHAR2(25), ... ... CONSTRAINT emp_email_uk UNIQUE(email)); ** The Oracle server enforces the UNIQUE constaint by implicityly creating a unique index on the unique key column or columns.

Column-level constraint: CREATE TABLE employees( employee_id NUMBER(6) CONSTRAINT emp_emp_id_pk PRIMARY KEY, first_name VARCHAR2(20), ...); Table-level constraint: CREATE TABLE employees( employee_id NUMBER(6), first_name VARCHAR2(20), ... job_id VARCHAR2(10) NOT NULL, CONSTRAINT emp_emp_id_pk PRIMARY_KEY(EMPLOYEE_ID));

Column-level constraint: CREATE TABLE employees( employee_id NUMBER(6) CONSTRAINT emp_emp_id_pk PRIMARY KEY, first_name VARCHAR2(20), ...); Table-level constraint: CREATE TABLE employees( employee_id NUMBER(6), first_name VARCHAR2(20), ... job_id VARCHAR2(10) NOT NULL, CONSTRAINT emp_emp_id_pk PRIMARY_KEY(EMPLOYEE_ID));

- NOT NULL - UNIQUE - PRIMARY KEY - FOREIGN KEY - CHECK You can name a constraint, or the Oracle server automatically generates a name by using the SYS_Cn All constraints are stored in the data dictionary. SYS_Cn n is an integer so that the constraint name is unique. Define a constraint at the column or table level. * Syntax CREATE TABLE [schema.]table (column datatype [DEFAULT expr] [column_con..

- NOT NULL - UNIQUE - PRIMARY KEY - FOREIGN KEY - CHECK You can name a constraint, or the Oracle server automatically generates a name by using the SYS_Cn All constraints are stored in the data dictionary. SYS_Cn n is an integer so that the constraint name is unique. Define a constraint at the column or table level. * Syntax CREATE TABLE [schema.]table (column datatype [DEFAULT expr] [column_con..

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하고 싶습니다.일주일에 한번이라도 괜찮습니다.제대로 한번 해보고 싶은데요..답글 남겨주세요.