what is the differances with SQL tables and relation modelling?

your er diagram could be of two types
1) logical: used to understand database conceptually, may not reflect actual no of table in database. for e.g when showing many to many relation we may show only 2 related entities in diagram
2) physical: user to show all table used in database. you can say all sql tables may be mapped to physical er diagram for e.g when showing many to many relation we may show all 3 entities in diagram

Relational modeling is the logical representation of the physical relation of the DB tables.

Relational modeling is the logical representation of the physical relation of the DB tables.

thank you for helps.