Each Non-clustered table has a data segment. All of the table's data is stored in the extents of its data segment. Each cluster has a data segment. The data of every table in the cluster is stored in the cluster's data segment.
A schema is collection of database objects of a User.
A schema is collection of database objects of an user and is used synonym of an user.
Schema name = user name
Yes a Tablespace can hold objects from different Schemes in Oracle
An integrity constraint is a declarative way to define a business rule for a column of a table.
A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE datablocks. Block size is specified in INIT.ORA file and can?t be changed latter.
A data block size is defined by DB_BLOCK parameter in pfile and there could be non standard block sizes supported by Oracle upto block size of 32bytes
Once set the block size could not be changed and the database has to be created again
Yes we can enforce integrity constraint on a table if some existing table does not satisfy the constraint by using "ENABLE NOVALIDATE"
Every ORACLE database contains a tablespace named SYSTEM, which is automatically created when the database is created. The SYSTEM tablespace always contains the data dictionary tables for the entire database.
The SYSTEM tablespace is created automatically for each new Oracle database. It contains all the data dictionary objects for the entire database.
The data dictionary of an ORACLE database is a set of tables and views that are used as a read-only reference about the database.
It stores information about both the logical and physical structure of the database, the valid users of an ORACLE database, integrity constraints defined for tables in the database and space allocated for a schema object and how much of it is being used.
NOT NULL Constraint - Disallows Nulls in a table's column.
UNIQUE Constraint - Disallows duplicate values in a column or set of columns.
PRIMARY KEY Constraint - Disallows duplicate values and Nulls in a column or set of columns.
FOREIGN KEY Constrain - Require each value in a column or set of columns match a value in a related table's UNIQUE or PRIMARY KEY.
CHECK Constraint - Disallows values that do not satisfy the logical expression of the constraint.