PL/SQL Add Column

Table Students

STUDENT_IDFIRST_NAMELAST_NAMEGENDERCITY
1DanielSCOTTMNew York
2AnthonySIMMONSMChicago
3SophiaTHOMPSONFLos Angeles

Add single column to table

ALTER TABLE STUDENTS 
  ADD country VARCHAR2(150);

Add columns to table

ALTER TABLE STUDENTS 
  ADD ( address VARCHAR2(4000),
        country VARCHAR2(150)
      );

Query the table

SELECT STUDENT_ID, FIRST_NAME, LAST_NAME, ADDRESS, COUNTRY FROM STUDENTS; 
STUDENT_IDFIRST_NAMELAST_NAMEADDRESSCOUNTRY
1DanielSCOTT
2AnthonySIMMONS
3SophiaTHOMPSON