MySQL LAG Function: Usage & Syntax

1 year ago
Sophia Anderson
2 minutes

The LAG function is a window function in MySQL that is used to retrieve data from a specified number of rows before the current row.

The syntax of the LAG function is as follows: LAG(expression, offset, default) OVER (PARTITION BY partition_expression ORDER BY sort_expression)

Description of Parameters:

  1. the column or expression that needs to be obtained.
  2. Number of rows to retrieve, which can be a positive, negative, or zero value. Positive numbers indicate fetching rows before the current row, negative numbers indicate fetching rows after the current row, and zero indicates fetching the current row.
  3. optional parameter that specifies the default value to return when the requested row does not exist.

The LAG function can be used to achieve various functions, such as:

  1. Retrieve the data from the previous line.
  2. Calculate the difference between the current row and the previous row.
  3. Get data from the previous few rows before the current row.
  4. Calculate the aggregate value of the current row and the data from the previous few rows.

Here is an example using the LAG function:

SELECT 
  id, 
  value, 
  LAG(value, 1, 0) OVER (ORDER BY id) AS lag_value 
FROM 
  table_name;

In this example, the LAG function is used to retrieve data from the previous row and return the result in a new column called “lag_value”.

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