Handling Missing Values

By default, if the transaction data set contains missing values for a variable that is common to both the master and the transaction data sets, then the MODIFY statement does not replace values in the master data set with missing values.
If you want to replace values in the master data set with missing values, then you use the UPDATEMODE= option in the MODIFY statement. UPDATEMODE= specifies whether missing values in a transaction data set replace existing values in a master data set.
The syntax for using the UPDATEMODE= option with the MODIFY statement follows:
BY by-variable;
MISSINGCHECK prevents missing values in ...

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