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230 lines
4.9 KiB
Markdown
230 lines
4.9 KiB
Markdown
# Built In Functions
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MySQL provides numerous built-in functions that streamline data manipulation and retrieval directly within your SQL queries.
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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.
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## Numeric Functions
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Optimize calculations directly in the database layer.
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```sql
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-- Rounds 5.73 to the nearest whole number.
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SELECT ROUND(5.73);
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```
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Output: 6
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```sql
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-- Rounds 5.73 to one decimal place.
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SELECT ROUND(5.73, 1);
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```
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Output: 5.7
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```sql
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-- Truncates 5.758 2 to two decimal places without rounding.
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SELECT TRUNCATE(5.7582, 2);
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```
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Output: 5.75
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```sql
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-- Returns the smallest integer greater than or equal to 5.2 .
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SELECT CEILING(5.2);
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```
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Output: 6
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```sql
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-- Returns the largest integer less than or equal to 5.7.
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SELECT FLOOR(5.7);
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```
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Output : 5
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```sql
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-- Returns the absolute value of -5.2.
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SELECT ABS(-5.2);
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```
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Output: 5.2
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```sql
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-- Generates a random floating-point number between 0 and 1. Useful for sampling or generating random data.
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SELECT RAND();
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```
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## String Functions
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Manipulate character data efficiently within queries.
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```sql
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-- Returns the length of the string 'sky'.
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SELECT LENGTH('sky');
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```
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Output: 3
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```sql
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-- Converts the string 'sky' to uppercase.
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SELECT UPPER('sky');
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```
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Output: SKY
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```sql
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-- Converts the string 'sky' to lowercase.
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SELECT LOWER('sky');
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```
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Output: sky
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```sql
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-- Removes leading spaces from ' sky'.
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SELECT LTRIM(' sky');
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```
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Output: sky
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```sql
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-- Removes trailing spaces from 'sky '.
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SELECT RTRIM('sky ');
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```
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Output: sky
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```sql
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-- Removes leading and trailing spaces from ' sky '.
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SELECT TRIM(' sky ');
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``` Output: sky
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```sql
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-- Extracts the leftmost 4 characters from 'Kindergarten'.
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SELECT LEFT('Kindergarten', 4);
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```
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Output: Kind
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```sql
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-- Extracts the rightmost 6 characters from 'Kindergarten'.
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SELECT RIGHT('Kindergarten', 6);
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```
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Output: garten
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```sql
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-- Extracts 5 characters from 'Kindergarten' starting at position 3.
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SELECT SUBSTRING('Kindergarten', 3, 5);
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```
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Output: nderg
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```sql
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-- Returns the position of the first occurrence of 'n' in 'Kindergarten'. Returns 0 if not found.
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SELECT LOCATE('n','Kindergarten');
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```
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Output: 3
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```sql
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-- Replaces all occurrences of 'garten' with 'garden' in 'Kindergarten'.
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SELECT REPLACE('Kindergarten', 'garten', 'garden');
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```
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Output: Kindergarden
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```sql
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-- Concatenates 'first' and 'last'.
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SELECT CONCAT('first', 'last');
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```
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Output: firstlast
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## Date Functions
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Retrieve and extract components of date and time values.
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```sql
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-- Returns the current date and time (YYYY-MM-DD HH:MI:SS format). [1]
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SELECT NOW();
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```
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Example Output: 2025-06-19 16:31:0 0
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```sql
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-- Returns the current date (YYYY-MM-DD format). [1]
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SELECT CURDATE();
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```
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Example Output: 2025-06-19
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```sql
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-- Returns the current time ( HH:MI:SS format). [1]
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SELECT CURTIME();
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```
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Example Output: 16:31:00
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```sql
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-- Extracts the month as a number from a date/datetime. [1]
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SELECT MONTH(NOW());
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```
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Example Output: 6
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```sql
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-- Extracts the year as a number from a date/datetime. [1]
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SELECT YEAR(NOW());
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```
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Example Output: 20 25
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```sql
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-- Extracts the hour as a number from a time/datetime. [1]
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SELECT HOUR(NOW());
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```
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Example Output: 16
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## Formatting Dates and Times
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Customize date and time output strings for application display.
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The default MySQL date format is "YYYY-MM-DD". Use `DATE_FORMAT()` and `TIME_FORMAT()` to control the output string representation.
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```sql
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-- Form ats the current date and time. [1, 4]
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SELECT DATE_FORMAT(NOW(), '%M %D %Y');
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```
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Example Output: June 19th 2025
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```sql
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-- Formats the current date with numeric month and day. [1, 4]
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SELECT DATE_FORMAT(NOW(), '%m %d %y');
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```
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Example Output: 06 19 25
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```sql
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-- Formats the current date with numeric month and day with English suffix. [1, 4]
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SELECT DATE_FORMAT(NOW(), '%m %D %y');
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```
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Example Output: 06 19th 2 5
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```sql
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-- Formats the current time. [1, 4]
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SELECT TIME_FORMAT(NOW(), '%H %i %p');
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```
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Example Output: 16 31 PM
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## Calculating Dates and Times
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Perform date and time arithmetic directly in queries.
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```sql
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-- Adds 1 day to the current date and time. [1, 2]
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SELECT DATE_ADD(NOW(), INTERVAL 1 DAY);
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```
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Example Output: 2025-06-20 16:31:00
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```sql
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-- Subtracts 1 year from the current date and time. [1, 2]
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SELECT DATE_ADD(NOW(), INTERVAL -1 YEAR);
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```
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Example Output: 2024-06-19 16:31:00
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```sql
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-- Also subtracts 1 year from the current date and time. [1, 2]
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SELECT DATE_SUB(NOW(), INTERVAL 1 YEAR);
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```
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Example Output: 2024-06-19 16:31 :00
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```sql
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-- Returns the difference in days between two dates. Time components are ignored for the difference calculation. [1, 7]
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SELECT DATEDIFF('2025-06-19 09:00', '2025-04-10 17:00');
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```
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Output: 70
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```sql
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-- Calculates the difference between two times in seconds by converting them to seconds past midnight. [5, 7]
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SELECT TIME_TO_SEC('09:00') - TIME_TO_SEC('09:02');
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```
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Output: -120
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