Oracle 문법 정리

🌱 오늘의 주제  : Oracle 문법 정리

 

 

 

 

 

 

 

 

 

🌱 Single Row Functions 

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• initcap : 첫 글자는 대문자로 변경

select initcap('hello my name is yuri')
from dual;

 

• length : 글자 수 출력

select length(ename) as length
from emp;

 

 

• substr: 글자 자르기 (첫 순서, 끝 순서)

select substr('hello', 2 ,2)
from dual;

 

 

 

 

 

 

 

 

🌱 Grouping Functions

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• NO group functions in where clause (Only single row functions allowed in WHERE clause) 
• 그 대신에, having을 사용!  groupy by 뒤에 사용합니다. 

 

 

<순서>

select column name

from  tables

where  conditions

group by column name

having  conditions

orer by conditions

 

 

 

 

 

 

🌱 SELECT within SELECT (Subqueries)

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Single-row subquery returns only one row.

 

 

 

 

 

 

 

🌱 Multi-Table Queries and Joins

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• Inner Join

select *
from emp INNER JOIN dept
ON emp.deptno = dept.deptno
;

 

 

 

• RIght Join

select *
from emp RIGHT JOIN dept
ON emp.deptno = dept.deptno
;

같은 의미 

select *
from emp RIGHT OUTER JOIN dept
ON emp.deptno = dept.deptno
;

 

• Left Join

select *
from emp LEFT JOIN dept
ON emp.deptno = dept.deptno
;

 

같은 의미 

select *
from emp LEFT OUTER JOIN dept
ON emp.deptno = dept.deptno
;

 

 

Left Join과 Right Join 할 때, 순서 주의하자!

 

 

 

 

 

 

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