Text compression in PostgreSQL

Question

I know in SQL we can compress the text field like the following:

CREATE TABLE TableName (FieldName CHARACTER(255) WITH COMPRESSION);

I want

Answer 1

Compression is enabled by default for all string types, you don't have to tell the database to do it. Check the manual about TOAST

• PLAIN prevents either compression or out-of-line storage; furthermore it disables use of single-byte headers for varlena types. This is the only possible strategy for columns of non-TOAST-able data types.
• EXTENDED allows both compression and out-of-line storage. This is the default for most TOAST-able data types. Compression will be attempted first, then out-of-line storage if the row is still too big.
• EXTERNAL allows out-of-line storage but not compression. Use of EXTERNAL will make substring operations on wide text and bytea columns faster (at the penalty of increased storage space) because these operations are optimized to fetch only the required parts of the out-of-line value when it is not compressed.
• MAIN allows compression but not out-of-line storage. (Actually, out-of-line storage will still be performed for such columns, but only as a last resort when there is no other way to make the row small enough to fit on a page.)