Which of the following is true of database? Please choose all that apply.

A$.$ Relational databases have a fixed schema that must be defined before data is entered.

B$.$ Denormalization combines tables in a database into a single table while normalization breaks a single table apart into many tables.

C$.$ Compared with normalization, denormalization make it easier to query your data.

D$.$ In a relational database, data is organized in a tabular format.

E$.$ A primary key is a column or group of columns in a table that provides a unique link between data in two tables.

F$.$ Denormalization reduces data redundancy, while normalization may introduce redundancy.

G$.$ SQL is a complete database language as well as a complete programming language such as PHP$.$