Library Concatenation

Definition

Concatenation is the logical combining of two or more libraries. Concatenation allows you to access the SAS data sets in several libraries with one libref.

You can concatenate two or more libraries by specifying their librefs or physical names in the LIBNAME statement or function.

Physical names must be enclosed in single or double quotation marks in a LIBNAME statement, otherwise SAS looks for a previously assigned libref with the same name.

In the following examples, summer, winter, spring fall and and annual are previously defined librefs:

libname annual (summer winter spring fall);

libname annual ('path1' 'path2' 'path3');

libname annual ('path' winter spring fall);

libname total (annual 'path');

How SAS Concatenates Library Members

When there are members of the same name in more than one library, the first occurrence of the member is used for input, update, output, renames and deletes.

This example contains three SAS data libraries, and each data library contains two SAS data files. The LIBNAME statement concatenates LIB1, LIB2 and LIB3:

LIBNAME fruit (lib1 lib2 lib3);

LIB1            LIB2             LIB3
----            ----             ----
apples          apples           oranges
pears           oranges          plums

The concatenated library FRUIT has the following members:

fruit
------
apples
pears
oranges
plums

Note: Output will always go to the first level. For example: "data fruit.oranges" writes to LIB1. [cautionend]

Note that in this example, if the file APPLES in LIB1 was a different file from the APPLES in LIB2 and an update to APPLES was specified, it will only be updated in LIB1 because that is the first occurence of the member APPLES.

For complete documentation on library concatenation, see the LIBNAME statement or function in SAS Procedures Guide.

For more information on how specific operating environments handle concatenation, see the SAS documentation for your operating environment.

Rules for Library Concatenation

After you create a library concatenation, you can specify the libref in any context that accepts a simple (nonconcatenated) libref. These rules determine how SAS files (that is, members of SAS libraries) are located among the concatenated libraries:

If you specify any options or an engine, they apply only to the libraries that you specified with the complete physical name, not to any library that you specified with a libref.
When a SAS file is opened for input or update, the concatenated libraries are searched and the first occurrence of the specified file is used.
When a SAS file is opened for output, it is created in the first library that is listed in the concatenation.
Note: A new SAS file is created in the first library even if there is a file with the same name in another part of the concatenation.
When you delete or rename a SAS file, only the first occurrence of the file is affected.
Any time a list of SAS files is displayed, only one occurrence of a filename is shown.
Note: Even if the name occurs multiple times in the concatenation, only the first occurrence is shown.
A SAS file that is logically connected to another file (such as an index to a data set) is listed only if the parent file resides in that same library. For example, if library ONE contains A.DATA, and library TWO contains A.DATA and A.INDEX, only A.DATA from library ONE is listed. (See rule 4.)
If any library in the concatenation is sequential, then all of the libraries are treated as sequential.
The attributes of the first library that is specified determine the attributes of the concatenation. For example, if the first SAS data library that is listed is "read only," then the entire concatenated library is "read only."
Once a libref has been assigned in a concatenation, any changes made to the libref will not affect the concatenation.

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