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hyeminjang/SQL.md

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+# SELECT
+
+* SELECT ALL
+
+```SQL
+SELECT*
+FROM employeeS
+```
+* SELECT Column and AS
+
+```SQL
+SELECT e.emp_name
+FROM employeeS as e
+```
+
+* Multiple
+```SQL
+SELECT city,state
+FROM station
+```
+
+
+# WHERE 
+
+* Condition
+
+```SQL
+SELECT *
+FROM city
+WHERE population > 100000
+AND countrycode = 'USA'
+```
+
+* Distinct & even number
+
+```SQL
+SELECT DISCTINCT city
+FROM station
+WHERE mod(city,2)=0
+```
+# NOT
+```sql
+SELECT city
+FROM station
+WHERE NOT (a<>0 or b<>0)
+```
+
+# COUNT
+
+```SQL
+SELECT count (city) - SELECT count (distinct city)
+FROM station
+```
+
+
+# LIKE & NOT LIKE
+
+```sql
+SELECT distinct s.city
+FROM station as
+WHERE city like 'a%'
+or city like 'e%'
+or city like 'i%'
+or city like 'o%'
+or city like 'u%'
+```
+
+```sql
+SELECT city
+FROM station
+WHERE city like '%\%%'
+```
+
+```sql
+SELECT city
+FROM station
+WHERE city like 'It''s'
+```
+
+> % : %\%%
+<br> ' : ''''
+
+* REGEXP
+
+* aeiou로 시작
+
+```sql
+SELECT DISTINCT city 
+FROM station
+WHERE city REGEXP '^a|^e|^i|^o|^u'
+```
+
+```sql
+SELECT DISTINCT city 
+FROM station
+WHERE city REGEXP '^[aeiou]'
+```
+
+* aeiou로 끝
+
+```sql
+SELECT distinct city
+FROM station
+WHERE city REGEXP 'a$|e$|i$|o$|u$'
+```
+
+```sql
+SELECT distinct city
+FROM station
+WHERE city REGEXP '[aeiou]$'
+```
+* a,e,i,o,u 로 시작 &  a,e,i,o,u 끝
+```sql
+SELECT distinct city
+FROM station 
+WHERE city REGEXP '^[aeiou]'
+and city REGEXP '[aeiou]$'
+```
+
+```sql
+SELECT distinct city
+FROM station 
+WHERE city REGEXP '^[aeiou].*[aeiou]$'
+```
+>. : 모든 char
+<br> * : 0 or more 
+
+# ORDER
+
+* 오름차순
+
+```sql
+SELECT city
+FROM station
+ORDER BY city asc
+```
+
+* 내림차순
+```sql
+SELECT city
+FROM station
+ORDER BY city desc
+```
+* 복수의 열
+```sql
+SELECT city
+FROM station
+ORDER BY a,b
+
+a>b순서대로 정렬
+```
+
+* NULL 값은 가장 작은 값
+
+# LIMIT
+
+* no를 내림차순 하면서 3행까지 출력
+```sql
+SELECT city
+FROM station
+ORDER BY no DESC
+LIMIT 3 
+```
+
+# OFFSET
+* 3건씩 총 3페이지 > 3페이지 표시
+
+```sql
+SELECT city
+FROM station
+LIMIT 3
+OFFSET 3
+```
+# CALCUTATION
+```sql
+SELECT city , PRICE * QUANTITY (AS) AMOUNT
+FROM station
+```
+```sql
+SELECT *
+, PRICE * QUANTITY "매출"
+FROM A
+```
+
+```SQL
+SELECT * 
+, PRICE * QUANTITY AS "금액"
+WHERE "금액" >= 2000
+FROM A
+[ERROR]
+
+WHERE > SELECT 순으로 처리
+WHERE 에서 사용한 "금액"은 처리 불가
+```
+
+* Calculation & Order
+```sql
+SELECT * 
+, price * quantity as amount
+FROM station
+ORDER BY amount DESC
+```
+
+# FUCTION
+## ROUND
+```sql
+SELECT *
+, ROUND (amout,1)
+FROM station
+```
+## CONCAT
+```SQL
+SELECT CONCAT (amoun,unit)
+FROM sample1
+```
+
+## SUBSTRING
+```SQL
+SUBSTRING('19900708',5,2)
+```
+## TRIM
+```SQL
+TRIM('ABC   ')
+```
+# DATE
+
+```SQL
+SELECT current_timestamp
+```
+```sql
+SELECT current_timestamp + 1day
+```
+
+```SQL
+DATEDIFF('2019-07-24','2019-01-01')
+```
+
+# CASE WEHN
+```SQL
+CASE
+WHEN 1 THEN '남자'
+WHEN 2 THEN '여자'
+END
+```
+
+```SQL
+SELECT a
+, CASE WEHN a IS NULL THEN 0
+ELSE a END
+"a(null=0)"
+FROM sample
+```
+* Result
+
+a|a(null=0)
+-|-
+1|2
+NULL|0
+
+* COALESCE
+```SQL
+SELECT a
+, COALESCE (a,0)
+FROM sample1
+```
+
+## Multple Case
+```sql
+update-ing
+
+SELECT a AS "코드"
+CASE
+    WHEN 1 = a THEN '남자'
+    WHEN 2 = a THEN '여자'
+    ELSE '미지정'
+END AS "성별" FROM sample1
+
+SELECT a AS "코드"
+CASE 
+    WHEN 1 THEN '남자'
+    WHEN 2 THEN '여자'
+    ELSE '미지정'
+END AS "성별" FROM sample1
+```
+
+# INSERT
+INSERT INTO city
+VALUES (1,'ABC','2019-07-24')
+
+INSERT INTO city (no, a)
+VALUES (2,'DEF')
+
+# REGULAR EXPRESSON
+```
+.       - Any Character Except New Line
+\d      - Digit (0-9)
+\D      - Not a Digit (0-9)
+\w      - Word Character (a-z, A-Z, 0-9, _)
+\W      - Not a Word Character
+\s      - Whitespace (space, tab, newline)
+\S      - Not Whitespace (space, tab, newline)
+
+\b      - Word Boundary
+\B      - Not a Word Boundary
+^       - Beginning of a String
+$       - End of a String
+
+[]      - Matches Characters in brackets
+[^ ]    - Matches Characters NOT in brackets
+|       - Either Or
+( )     - Group
+
+Quantifiers:
+*       - 0 or More
++       - 1 or More
+?       - 0 or One
+{3}     - Exact Number
+{3,4}   - Range of Numbers (Minimum, Maximum)
+```