What is data integrity and how it is differ from data validity?

 Data validity deals with data that is input into a system (ex. a database) while data integrity deals with the maintenance of that data once it has been entered into the system.

data integrity is a fundamental component of information security. In its broadest used, "data integrity" refers to the accuracy and consistency of data stored in database, data warehouse, data mark or other construct.

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This is clearly explained.
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Below find the requested details along with example Data validity : The purpose of this test is to verify the validity of the data that is stored in the database.
Some examples are mentioned below.
• Compare data in the target dataset • Compare the number of records and validate legitimacy of any differences • Verify how NULL/empty field values are handled • Verify how special characters or code snippets are handled • Check that the right columns in the right tables are being updated • Data type: E.g.
feed text or a number into a date field • Data format: E.g.
MMDDYYYY instead of DDMMYYYY • Default values • Data range: E.g.
account number outside the specified accepted range • Data length: E.g.
longer string than accepted in field.
Is the data truncated or refused? Data integrity: Data integrity ensures the quality of the data in the database.
i.e.
verification of referential integrity and the application of constraints (e.g.
foreign / primary keys).
• CRUD: Create, retrieve, update, delete.
When a value undergoes any of the above actions the database should be verified for the changes performed on related entities, such as foreign and primary keys and all dependent entities.
• Primary keys should not be allowed to be equal for two rows in a table • Primary keys should not allowed to be NULL or empty • Any other keys that must be unique in their column or set of columns • Any other values that are not supposed to be NULL or empty.
• Values that are outside a limited set of allowed values (other than range).
• Referential integrity: relationships between foreign keys and primary keys or between foreign keys and unique keys (through foreign key and check constraints).
This requires verification of the consistency of key values across tables.
I.e.
no references to nonexistent values should exist, and if a key value changes, all references to it change consistently throughout the database.
• It should not be possible to add a record in the related table if there is no associated record in the primary table.
• It should not be possible to change a specified column value in primary table, if that column is a foreign key of a related table.
• It should not be possible to delete records from the primary table if there are matching records in a related table.
• Check integrity.
Check integrity constraints are used to limit the value range that can be placed in a column.
If a check constraint is defined on a single column, it should not be allowed to feed values that are outside a limited set of allowed values into this column.