**SQL built-in functions** are pre-defined functions that can be used to manipulate and perform operations on data stored in a database. These functions can be used to perform a wide range of tasks, such as performing calculations, transforming data, formatting data, and extracting data. They are an essential tool for data analysts, database administrators, and developers who work with databases.

## Benefits of using SQL built-in functions

Using SQL built-in functions has several benefits, including:

**Improved productivity:** Built-in functions can simplify complex calculations and transformations, making it easier and quicker to work with data.

**Increased accuracy:** Built-in functions are pre-defined and thoroughly tested, which helps to ensure that the calculations and transformations are accurate and consistent.

**Better performance:** SQL built-in functions are optimized for performance, which means they can process large datasets quickly and efficiently.

**Easier maintenance:** Since built-in functions are part of the SQL language, they can be used across different database management systems, making it easier to maintain and share code across different projects and teams.

**SQL functions** are used to perform calculations and manipulations on data stored in a relational database. There are many types of SQL functions, including aggregate functions, date functions, string functions, ranking functions, analytical functions, and math functions.

### Aggregate Functions

Aggregate functions are used to perform calculations on a set of values and return a single value as the result. The most commonly used aggregate functions in SQL are:

Name | Description |
---|---|

COUNT | counts the number of rows in a specified column or table. |

SUM | calculates the sum of all values in a specified column. |

AVG | calculates the average value of a specified column. |

MAX | returns the maximum value in a specified column. |

MIN | returns the minimum value in a specified column. |

### DATE Functions

Date functions are used to manipulate and format dates and times in SQL. Some commonly used date functions include:

Name | Description |
---|---|

CURRENT_TIMESTAMP | Returns the current date and time as a datetime value. It includes the date and time down to the millisecond. |

CURRENT_TIMEZONE | Returns the current time zone offset as a signed integer. The value is expressed in minutes and can be positive or negative. |

DATEADD | Adds a specified number of date and time intervals to a given date. You can add seconds, minutes, hours, days, weeks, months, quarters, or years. |

DATEDIFF | Calculates the difference between two dates. You can specify the units of time you want to use, such as seconds, minutes, hours, days, weeks, months, quarters, or years. |

DATEPART | Extracts a specific part of a date and time value, such as the year, month, day, hour, minute, or second. |

GETDATE | Returns the current system date and time as a datetime value. |

ISDATE | Tests whether a given expression is a valid date or not. It returns 1 if the expression is a valid date, and 0 if it is not. |

DAY | Returns the day of the month from a given date. |

MONTH | Returns the month from a given date. |

YEAR | Returns the year from a given date. |

### String Functions

String functions are used to manipulate text data in SQL. Some commonly used string functions include:

Name | Description |
---|---|

CONCAT | Is used to combine two or more strings into a single string. |

SUBSTRING | Is used to extract a part of a string, starting at a specified position and for a specified length. |

LEN | Is used to find the length of a string. It returns the number of characters in the string. |

REPLACE | Replace all occurrences of a specified string with another string in a given string. |

UPPER | Convert all the characters in a string to uppercase. |

LOWER | Convert all the characters in a string to lowercase. |

TRIM | Is used to remove any leading or trailing spaces from a string. It can also remove any other specified characters. |

### Math Functions

Math functions are used to perform mathematical operations on numerical data in SQL. Some commonly used math functions include:

Name | Description |
---|---|

ABS | Returns the absolute value of a number. |

ROUND | Rounds a number to a specified number of decimal places. |

CEILING | Returns the smallest integer greater than or equal to a specified number. |

FLOOR | Returns the largest integer less than or equal to a specified number. |

SQRT | Returns the square root of a number. |

POWER | This function calculates the result of raising a number to a certain power. |

SIGN | This function returns the sign of a number. It returns 1 if the number is positive, -1 if it is negative, and 0 if the number is zero. |

LOG | This function calculates the natural logarithm of a number. |

EXP | Calculates the exponential value of a number. |

### Ranking Functions

Ranking functions are used to assign a rank to each row in a result set based on the values in a specific column or set of columns. Ranking functions are particularly useful in situations where you need to determine the top or bottom N rows based on a certain criteria, or to calculate percentiles for a set of values.

Name | Description |
---|---|

CUME_DIST() | Clculates the cumulative distribution of a value within a group of values. It returns the percentage of values that are less than or equal to the current value. |

RANK() | Assigns a rank to each distinct value within a group of rows, leaving gaps in the ranking sequence if there are ties. |

DENSE_RANK() | Assigns a rank to each distinct value within a group of rows, with no gaps in the ranking. It is similar to RANK(), but it does not leave gaps in the ranking sequence. |

NTILE() | Divides the rows in a result set into a specified number of groups, assigning each row a group number. Each group contains an equal number of rows as far as possible. |

PERCENT_RANK() | Calculates the rank of a row as a percentage of the total number of rows in the result set. It returns a value between 0 and 1, with 0 being the lowest rank and 1 being the highest. |

ROW_NUMBER() | Assigns a unique number to each row within a result set, with no regard for the values in the columns. The numbering starts at 1 and increments by 1 for each row. |

### Analytical Functions

Analytical functions are used to perform complex calculations and analysis on a result set, without grouping the data. Analytical functions can be used to calculate running totals, moving averages, and other aggregate values over a specific window or group of rows.

Name | Description |
---|---|

RANK() | Assigns a rank to each row based on a specified criteria. |

DENSE_RANK() | Assigns a rank to each row, but with no gaps in the ranking sequence. |

ROW_NUMBER() | Assigns a unique number to each row in the result set. |

LAG() | Returns the value of a column from the previous row. |

LEAD() | Returns the value of a column from the next row. |

FIRST_VALUE() | Retrieve the first value of an ordered set of rows. |

LAST_VALUE() | Retrieve the last value of an ordered set of rows. |

### Window Functions

Window functions operate on a specific subset of rows in a result set and return a value for each row, based on calculations performed over a window or group of rows. Window functions are used to perform complex analysis on the data and return aggregate or summary information without grouping the data. They provide a flexible way of calculating aggregates and ranking over a set of rows, without requiring you to group by any specific column. Some examples of window functions include:

Name | Description |
---|---|

ROW_NUMBER() | This function assigns a unique sequential number to each row in a result set based on a specified ordering. |

RANK() | This function assigns a rank to each row within a result set based on the values of a specified column. |

DENSE_RANK() | This function is similar to RANK(), but it assigns consecutive ranks to rows with the same values. |

In conclusion, SQL functions are essential in manipulating and extracting data from a database. By understanding and utilizing various types of SQL functions, you can effectively query and manipulate data to get the results you need.