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# Built In Functions

MySQL  provides numerous built-in functions that streamline data manipulation and retrieval directly within your SQL queries.

Utilizing these functions minimizes application-level processing, leading to more robust and performant code. This guide covers essential MySQL functions, focusing on their practical utility for Java developers.

## Numeric Functions

Optimize calculations directly in the database layer.

```sql
-- Rounds 5.73 to the nearest whole number.
SELECT ROUND(5.73);
```
Output: 6

```sql
-- Rounds 5.73 to one decimal place.
SELECT ROUND(5.73, 1);
```
Output: 5.7

```sql
-- Truncates 5.758 2 to two decimal places without rounding.
SELECT TRUNCATE(5.7582, 2);
```
Output: 5.75

```sql
-- Returns the smallest integer greater than or equal to 5.2 .
SELECT CEILING(5.2);
```
Output: 6

```sql
-- Returns the largest integer less than or equal to 5.7.
SELECT FLOOR(5.7);
```
Output : 5

```sql
-- Returns the absolute value of -5.2.
SELECT ABS(-5.2);
```
Output: 5.2

```sql
-- Generates a random floating-point number  between 0 and 1. Useful for sampling or generating random data.
SELECT RAND();
```

## String Functions

Manipulate character data efficiently within queries.

```sql
-- Returns the length of the string 'sky'.
SELECT  LENGTH('sky');
```
Output: 3

```sql
-- Converts the string 'sky' to uppercase.
SELECT UPPER('sky');
```
Output: SKY

```sql
-- Converts the string 'sky'  to lowercase.
SELECT LOWER('sky');
```
Output: sky

```sql
-- Removes leading spaces from '    sky'.
SELECT LTRIM('    sky');
```
Output: sky

```sql
-- Removes  trailing spaces from 'sky    '.
SELECT RTRIM('sky    ');
```
Output: sky

```sql
-- Removes leading and trailing spaces from '   sky  '.
SELECT TRIM('   sky  ');
``` Output: sky

```sql
-- Extracts the leftmost 4 characters from 'Kindergarten'.
SELECT LEFT('Kindergarten', 4);
```
Output: Kind

```sql
-- Extracts the rightmost 6 characters from 'Kindergarten'.
SELECT RIGHT('Kindergarten', 6);
```
Output: garten

```sql
-- Extracts 5 characters from 'Kindergarten' starting at position 3.
SELECT SUBSTRING('Kindergarten', 3,  5);
```
Output: nderg

```sql
-- Returns the position of the first occurrence of 'n' in 'Kindergarten'. Returns 0 if not found.
SELECT LOCATE('n','Kindergarten');
```
Output: 3

```sql
-- Replaces all occurrences of 'garten' with 'garden' in 'Kindergarten'.
SELECT REPLACE('Kindergarten', 'garten', 'garden');
```
Output: Kindergarden

```sql
-- Concatenates 'first' and 'last'.
SELECT CONCAT('first', 'last');
```
Output: firstlast

## Date Functions

Retrieve and extract components of date and time values.

```sql
--  Returns the current date and time (YYYY-MM-DD HH:MI:SS format). [1]
SELECT NOW();
```
Example Output: 2025-06-19 16:31:0 0

```sql
-- Returns the current date (YYYY-MM-DD format). [1]
SELECT CURDATE();
```
Example Output: 2025-06-19

```sql
-- Returns the current time ( HH:MI:SS format). [1]
SELECT CURTIME();
```
Example Output: 16:31:00

```sql
-- Extracts the month as a number from a date/datetime. [1]
SELECT MONTH(NOW());
```
Example Output: 6

```sql
-- Extracts the year as a number from a date/datetime. [1]
SELECT YEAR(NOW());
```
Example Output: 20 25

```sql
-- Extracts the hour as a number from a time/datetime. [1]
SELECT HOUR(NOW());
```
Example Output: 16

## Formatting Dates and Times

Customize date and time output strings  for application display.

The default MySQL date format is "YYYY-MM-DD". Use `DATE_FORMAT()` and `TIME_FORMAT()` to control the output string representation.

```sql
-- Form ats the current date and time. [1, 4]
SELECT DATE_FORMAT(NOW(), '%M %D %Y');
```
Example Output: June 19th 2025

```sql
-- Formats the current  date with numeric month and day. [1, 4]
SELECT DATE_FORMAT(NOW(), '%m %d %y');
```
Example Output: 06 19 25

```sql
-- Formats  the current date with numeric month and day with English suffix. [1, 4]
SELECT DATE_FORMAT(NOW(), '%m %D %y');
```
Example Output: 06 19th 2 5

```sql
-- Formats the current time. [1, 4]
SELECT TIME_FORMAT(NOW(), '%H %i %p');
```
Example Output: 16 31 PM

## Calculating  Dates and Times

Perform date and time arithmetic directly in queries.

```sql
-- Adds 1 day to the current date and time. [1, 2]
SELECT DATE_ADD(NOW(), INTERVAL 1 DAY);
```
Example Output: 2025-06-20 16:31:00

```sql
-- Subtracts 1 year from the current date and time. [1, 2]
SELECT DATE_ADD(NOW(), INTERVAL -1 YEAR);
```
Example Output: 2024-06-19 16:31:00

```sql
-- Also subtracts 1 year from  the current date and time. [1, 2]
SELECT DATE_SUB(NOW(), INTERVAL 1 YEAR);
```
Example Output: 2024-06-19 16:31 :00

```sql
-- Returns the difference in days between two dates. Time components are ignored for the difference calculation. [1, 7]
SELECT DATEDIFF('2025-06-19  09:00', '2025-04-10 17:00');
```
Output: 70

```sql
-- Calculates the difference between two times in seconds by converting  them to seconds past midnight. [5, 7]
SELECT TIME_TO_SEC('09:00') - TIME_TO_SEC('09:02');
```
Output: -120