Most commonly used SQL functions

SQL provides a wide range of built-in functions to manipulate and perform operations on data within your database. Here are some of the most commonly used SQL functions:

1. `SELECT` Functions:

- `COUNT()`: Counts the number of rows or non-null values in a column.

- `SUM()`: Calculates the sum of values in a column.

- `AVG()`: Computes the average of values in a column.

- `MIN()`: Returns the minimum value in a column.

- `MAX()`: Returns the maximum value in a column.

2. `WHERE` Functions:

- `LIKE`: Searches for a specified pattern in a column.

- `IN()`: Specifies multiple values for comparison.

- `BETWEEN`: Filters results within a specified range.

- `NULL`: Checks for NULL values.

- `IS NULL` / `IS NOT NULL`: Tests for NULL values.

3. String Functions:

- `CONCAT()`: Concatenates two or more strings.

- `SUBSTRING()`: Extracts a portion of a string.

- `LENGTH()` or `LEN()`: Returns the length of a string.

- `UPPER()`: Converts a string to uppercase.

- `LOWER()`: Converts a string to lowercase.

- `TRIM()`: Removes leading and trailing spaces.

4. Date and Time Functions:

- `GETDATE()` / `NOW()`: Retrieves the current date and time.

- `DATEPART()`: Extracts a specific part (year, month, day, etc.) from a date.

- `DATEDIFF()`: Calculates the difference between two dates.

- `DATEADD()`: Adds or subtracts a specific time interval from a date.

5. Aggregation Functions:

- `GROUP BY`: Groups rows based on a specified column.

- `HAVING`: Filters grouped rows.

- `SUM()`, `AVG()`, `MIN()`, `MAX()`: Used with `GROUP BY` to perform aggregate calculations.

6. Conditional Functions:

- `CASE`: Performs conditional logic within SQL queries.

- `COALESCE()`: Returns the first non-null value in a list of expressions.

- `NULLIF()`: Compares two expressions and returns null if they are equal.

7. Conversion Functions:

- `CAST()`: Converts one data type into another.

- `CONVERT()`: Converts one data type into another, with additional formatting options.

8. Mathematical Functions:

- `ABS()`: Returns the absolute value of a number.

- `ROUND()`: Rounds a number to a specified number of decimal places.

- `FLOOR()`: Returns the largest integer less than or equal to a number.

- `CEIL()` or `CEILING()`: Returns the smallest integer greater than or equal to a number.

These are some of the most commonly used SQL functions, and they play a crucial role in performing various operations, filtering data, aggregating results, and transforming data within a relational database.