In PostgreSQL, the `trunc()`

function is used to truncate a number to a specified number of decimal places. The syntax of the `trunc()`

function is `trunc(value, decimal_places)`

, where `value`

is the number to truncate and `decimal_places`

is the number of decimal places to truncate to.

For example, if you have a number 5.6789 and you want to truncate it to two decimal places, you can use the `trunc()`

function like this: `SELECT trunc(5.6789, 2);`

. This will return the result 5.67.

It's important to note that the `trunc()`

function does not round the number, it simply removes the extra decimal places. If you want to round the number instead of truncating it, you can use the `round()`

function in PostgreSQL.

Overall, the `trunc()`

function is useful for controlling the precision of numbers in PostgreSQL queries and calculations.

## What is the difference between the trunc() function and the floor() function in PostgreSQL?

The trunc() function in PostgreSQL is used to truncate a number to a specified number of decimal places, removing any extra digits beyond the specified number. For example, trunc(10.345, 2) would return 10.34.

The floor() function, on the other hand, is used to round a number down to the nearest integer less than or equal to the given number. For example, floor(10.345) would return 10.

In summary, the main difference between the trunc() and floor() functions is that trunc() allows you to specify the number of decimal places to truncate to, while floor() always rounds down to the nearest integer.

## What is the data type returned by the trunc() function in PostgreSQL?

The trunc() function in PostgreSQL returns a double precision data type.

## What is the default behavior of the trunc() function in PostgreSQL?

The default behavior of the trunc() function in PostgreSQL is to truncate a number to zero decimal places. This means that the function will remove any digits after the decimal point and return the integer part of the number.

## How to handle NULL values with the trunc() function in PostgreSQL?

When using the `trunc()`

function in PostgreSQL, you can handle NULL values by using the COALESCE function to replace any NULL values with a specified default value.

Here is an example query that demonstrates how to handle NULL values with the `trunc()`

function:

```
1
``` |
```
SELECT TRUNC(COALESCE(column_name, 0), 2) FROM table_name;
``` |

In this query, the `COALESCE()`

function is used to check if the `column_name`

has a NULL value. If it does, the `COALESCE()`

function will replace it with the default value of 0. Then, the `TRUNC()`

function is applied to truncate the value to 2 decimal places.

This approach ensures that the `trunc()`

function does not encounter any NULL values, preventing any potential errors in the query execution.

## How to truncate numbers towards zero with the trunc() function in PostgreSQL?

The `trunc()`

function in PostgreSQL is used to truncate a number to a specified number of decimal places. To truncate numbers towards zero using the `trunc()`

function, you can specify a negative number of decimal places.

Here's an example of how to truncate a number towards zero using the `trunc()`

function in PostgreSQL:

1 2 |
SELECT trunc(123.456, -2); -- Output: 100 SELECT trunc(-123.456, -2); -- Output: -100 |

In the above examples, the `trunc()`

function is used to truncate the number `123.456`

to two decimal places towards zero. The result of the first query is `100`

and the result of the second query is `-100`

. This means that the numbers are truncated towards zero without rounding.

## How to truncate a timestamp in PostgreSQL?

To truncate a timestamp to a specific level of precision in PostgreSQL, you can use the `DATE_TRUNC`

function.

For example, if you want to truncate a timestamp to the nearest hour, you can use the following query:

1 2 |
SELECT DATE_TRUNC('hour', timestamp_column) AS truncated_timestamp FROM your_table; |

Similarly, you can truncate the timestamp to other levels of precision such as day, week, month, etc. by replacing 'hour' in the query with the desired precision.

Here are a few examples:

- Truncate to the nearest day:

1 2 |
SELECT DATE_TRUNC('day', timestamp_column) AS truncated_timestamp FROM your_table; |

- Truncate to the nearest week:

1 2 |
SELECT DATE_TRUNC('week', timestamp_column) AS truncated_timestamp FROM your_table; |

- Truncate to the nearest month:

1 2 |
SELECT DATE_TRUNC('month', timestamp_column) AS truncated_timestamp FROM your_table; |

- Truncate to the nearest year:

1 2 |
SELECT DATE_TRUNC('year', timestamp_column) AS truncated_timestamp FROM your_table; |

You can adjust the precision as needed based on your requirements.