SAP Table Types

I. Transparent tables (BKPF, VBAK, VBAP, KNA1, COEP)

• Allows secondary indexes (SE11->Display Table->Indexes)
• Can be buffered (SE11->Display Table->technical settings) Heavily updated tables should not be buffered.

II. Pool Tables (match codes, look up tables)

• Should be accessed via primary key or
• Should be buffered (SE11->Display Table->technical settings)
• No secondary indexes
• Select * is Ok because all columns retrieved anyway

III. Cluster Tables (BSEG,BSEC)

• Should be accessed via primary key - very fast retrieval otherwise very slow
• No secondary indexes
• Select * is Ok because all columns retrieved anyway. Performing an operation on multiple rows is more efficient than single row operations. Therefore you still want to select into an internal table. If many rows are being selected into the internal table, you might still like to retrieve specific columns to cut down on the memory required.
• Statistical SQL functions (SUM, AVG, MIN, MAX, etc) not supported
• Can not be buffered

IV. Buffered Tables (includes both Transparent & Pool Tables)

While buffering database tables in program memory (SELECT into internal table) is generally a good idea for performance, it is not always necessary. Some tables are already buffered in memory. These are mostly configuration tables. If a table is already buffered, then a select statement against it is very fast. To determine if a table is buffered, choose the 'technical settings' soft button from the data dictionary display of a table (SE12). Pool tables should all be buffered.