SQL Server Video
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2024, November 12, Tuesday

#016 How to Count Dates of Different Records in SQL Server

Nesse vídeo apresentamos como contar os dias entre datas de registros diferentes, nesse exemplo, calcular a quantidade de dias entre as alterações ocorridas em versões de documentos

We'll get to know the techniques:

1. Get value from previous record (LAG, OVER, PARTITION, ORDER BY):

The LAG function is used to get the value of a column from the previous row in a result set. The OVER clause with the PARTITION BY and ORDER BY options helps define the window in which the LAG function operates. This is useful for calculating differences or trends over consecutive records.
Example:
```
SELECT
  Column1,
  LAG(Column1) OVER (PARTITION BY Category ORDER BY DateColumn) AS PreviousValue
FROM
  YourTable;
```

2. Count the number

of days between dates (DATEDIFF):

The DATEDIFF function is used to calculate the difference between two dates in terms of a specific unit, such as days, months, or years.
Example:
```
SELECT
  DATEDIFF(DAY, StartDate, EndDate) AS DayDifference
FROM
  YourTable;
```

3. Handle Registry Null Values (

ISNULL):

The ISNULL function is used to replace null values with an alternate value. This is useful for ensuring that the query results do not contain unwanted null values.
Example:
```
SELECT
  Column1,
  ISNULL(Column1, Alternate Value) AS NonNullValue
FROM
  YourTable;
```
In this example, if Column1 is null, 'Alternate Value' is returned.

These functionalities are commonly used for data manipulation and analysis in Microsoft SQL Server.