ready for rewrite of content

2025-06-19 12:14:28 -04:00
parent c718fb3fa9
commit 89c04a328f
23 changed files with 417 additions and 138 deletions
--- a/landing/docs/SQL-101/old/018-essential-mysql-functions.md
+++ b/landing/docs/SQL-101/old/018-essential-mysql-functions.md
@@ -0,0 +1,191 @@
+# Essential MySQL Functions 
+
+MySQL has many built-in functions. We will covering some important most used built-in functions; for a complete list refer to the online MySQL Reference Manual (http://dev.mysql.com/doc/).
+
+> NOTE: As of now we will be going through only function and their output, as they would be self explanatory.
+
+## Numeric Functions
+```sql
+SELECT ROUND(5.73)
+   ```
+6
+
+```sql
+SELECT ROUND(5.73, 1)
+   ```
+5.7
+
+```sql
+SELECT TRUNCATE(5.7582, 2)
+   ```
+5.75
+
+```sql
+SELECT CEILING(5.2)
+   ```
+6
+
+```sql
+SELECT FLOOR(5.7)
+   ```
+5
+
+```sql
+SELECT ABS(-5.2)
+   ```
+5.2
+
+```sql
+SELECT RAND() -- Generates a random floating point number b/w 0 & 1
+   ```
+
+## STRING Functions
+```sql
+SELECT LENGTH('sky')
+   ```
+3
+
+```sql
+SELECT UPPER('sky')
+   ```
+SKY
+
+```sql
+SELECT LOWER('sky)
+   ```
+sky
+
+```sql
+SELECT LTRIM('    sky')
+   ```
+sky
+
+```sql
+SELECT RTRIM('sky    ')
+   ```
+sky
+
+```sql
+SELECT TRIM('   sky  ')
+   ```
+sky
+
+```sql
+SELECT LEFT('Kindergarten', 4)
+   ```
+Kind
+
+```sql
+SELECT RIGHT('Kindergarten', 6)
+   ```
+garten
+
+```sql
+SELECT SUBSTRING('Kindergarten', 3, 5) 
+   ```
+nderg
+
+```sql
+SELECT LOCATE('n','Kindergarten') -- LOCATE returns the first occurrence of a character or character string, if found, otherwise it returns 0
+   ```
+3
+
+```sql
+SELECT REPLACE('Kindergarten', 'garten', 'garden')
+   ```
+Kindergarden
+
+```sql
+SELECT CONCAT('first', 'last')
+   ```
+firstlast
+
+## DATE Functions
+```sql
+SELECT NOW()
+   ```
+2021-10-21 19:59:47
+
+```sql
+SELECT CURDATE()
+   ```
+2021-10-21
+
+```sql
+SELECT CURTIME()
+   ```
+20:01:12
+
+```sql
+SELECT MONTH(NOW())
+   ```
+10
+
+```sql
+SELECT YEAR(NOW())
+   ```
+2021
+
+```sql
+SELECT HOUR(NOW())
+   ```
+13
+
+```sql
+SELECT DAYTIME(NOW())
+   ```
+Thursday
+
+## Formatting Dates and Times
+
+> In MySQL, the default date format is "YYYY-MM-DD", ex: "2025-05-12", MySQL allows developers to format it the way they want. We will discuss some of them.
+```sql
+SELECT DATE_FORMAT(NOW(), '%M %D %Y')
+   ```
+October 22nd 2021
+
+```sql
+SELECT DATE_FORMAT(NOW(), '%m %d %y')
+   ```
+10 22 21 
+
+```sql
+SELECT DATE_FORMAT(NOW(), '%m %D %y')
+   ```
+10 22nd 21 
+
+```sql
+SELECT TIME_FORMAT(NOW(), '%H %i %p')
+   ```
+14:11 PM
+
+## Calculating Dates and Times
+
+```sql
+SELECT DATE_ADD(NOW(), INTERVAL 1 DAY) --return tomorrows date and time
+   ```
+
+2021-10-23 14:26:17
+
+```sql
+SELECT DATE_ADD(NOW(), INTERVAL -1 YEAR)
+   ```
+or
+```sql
+SELECT DATE_SUB(NOW(), INTERVAL 1 YEAR)
+   ```
+> Both the queries will return the same output
+
+2020-10-22 14:29:47
+
+```sql
+SELECT DATEDIFF('2021-09-08 09:00', '2021-07-07 17:00') -- It will return the difference in number of days, time won't be considered
+   ```
+
+63
+
+```sql
+SELECT TIME_TO_SEC('09:00') - TIME_TO_SEC('09:02')
+   ```
+-120
+