Back Filling and Forward Filling
Learn how to fill missing data using SQL.
We'll cover the following...
Overview
Missing data can result from legitimate causes or bugs, but either way, we have to deal with it. To make the analysis easier and to reduce the risk of potential errors caused by mishandling missing values, we sometimes want to fill missing data with other values.
Filling constant values
The most straightforward way to fill in missing data is to replace it with a constant value. To replace NULL
values with a constant, we can use CASE
:
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SELECTn,v,CASE WHEN v IS NULL THEN 'X' ELSE v END AS adjusted_valueFROM (VALUES(1, 'A' ),(2, 'B' ),(3, null),(4, 'D' ),(5, null),(6, null),(7, 'G' )) AS t(n, v);
The CASE
expression returns the constant value X
when the value in the ...
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