Match-Merge Processing (1)

Merging SAS Data Sets

Match-Merge Processing

The examples in this lesson are straightforward. However, match-merging can be more complex, depending on your data and the output data set you want to create. To predict the results of match-merges correctly, you need to understand how the DATA step performs match-merges.

When you submit a DATA step, it is processed in two phases:

the compilation phase, in which SAS software checks the syntax of the SAS statements and compiles them (translates them into machine code). During this phase, SAS software also sets up descriptor information for the output data set and creates the program data vector (PDV), an area of memory where SAS software builds your data set, one observation at a time.

compilation phase

the execution phase, in which the DATA step reads data and executes any subsequent programming statements. When the DATA step executes, data values are read into the appropriate variables in the program data vector. From here, the variables are written to the output data set as a single observation.

execution phase

The following pages cover DATA step processing in greater detail. In them, you learn

how the DATA step sets up the new output data set
what happens when variables in different data sets have the same name
how the DATA step matches observations in input data sets
what happens when observations don't match
how missing values are handled.