Note:
1. In Table Level constraints DEFAULT and NOT NULL constraints are not allowed.
2. The below approach is applicable only when there is no data available in the table.
Step1: Create any table with out any constraints
Example:CREATE TABLE DEPT (DEPTNO INT,DNAME VARCHAR(20),LOC VARCHAR(20))
Step2: Make a single column as NOT NULL for which we want provide Primary Key constraint.
Syntax: ALTER TABLE TABLENAME ALTER COLUMN COLUMNNAME DATATYPE NOT NULL
Example1: ALTER TABLE DEPT ALTER COLUMN DEPTNO INT NOT NULL.
Step3: Add your required constraints to columns expect DEFAULT and NOT NULL by using the following approach.
Syntax: ALTER TABLE TABLENAME ADD CONSTRAINTTYPE (COLUMN1),CONSTRAINTTYPE (COLUMN2),...
Example1: ALTER TABLE DEPT ADD PRIMARY KEY(DEPTNO),UNIQUE(DNAME)
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