1. Keywords and Parameters

   table_ constraint	The table_constraint syntax is part of the table definition. An integrity constraint defined with this syntax can impose rules on any columns in the table.   The table_constraint syntax can appear in a CREATE TABLE or ALTER TABLE statement. This syntax can define any type of integrity constraint except a NOT NULL constraint.
   column_ constraint	The column_constraint syntax is part of a column definition. Usually, an integrity constraint defined with this syntax can impose rules only on the column in which it is defined. The column_constraint syntax that appears in a CREATE TABLE or ALTER TABLE ADD statement can define any type of integrity constraint. Column_constraint syntax that appears in an ALTER TABLE MODIFY column_options statement can only define or remove a NOT NULL constraint.
   CONSTRAINT	identifies the integrity constraint by the name constraint.  If you do not specify NULL or NOT NULL in a column definition, NULL is the default.
   UNIQUE	designates a column or combination of columns as a unique key. To satisfy a UNIQUE constraint, no two rows in the table can have the same value for the unique key. However, the unique key made up of a single column can contain nulls. A composite unique key is made up of a combination of columns. To define a composite unique key, you must use table_constraint syntax rather than column_constraint syntax. Any row that contains nulls in all key columns automatically satisfies the constraint. However, two rows that contain nulls for one or more key columns and the same combination of values for the other key columns violate the constraint. You cannot designate the same column or combination of columns as both a unique key and a primary key.
   PRIMARY KEY	designates a column or combination of columns as the table's primary key. A composite primary key is made up of a combination of columns. To define a composite primary key, you must use the table_constraint syntax rather than the column_constraint syntax. A table can have only one primary key. No primary key value can appear in more than one row in the table. No column that is part of the primary key can contain a null. You cannot designate the same column or combination of columns as both a primary key and a unique key
   NULL NOT NULL	determines whether a column can contain nulls. You must specify NULL and NOT NULL with column_constraint syntax, not with table_constraint syntax.
   	NULL	specifies that a column can contain null values. The NULL keyword does not actually define an integrity constraint. If you do not specify either NOT NULL or NULL, the column can contain nulls by default.
   	NOT NULL	specifies that a column cannot contain null values. To satisfy this constraint, every row in the table must contain a value for the column.
   Referential integrity constraints	Referential integrity constraints designate a column or combination of columns as the foreign key and establish a relationship between that foreign key and a specified primary or unique key, called the referenced key. The table containing the foreign key is called the child table, and the table containing the referenced key is called the parent table. The foreign key and the referenced key can be in the same table. In this case, the parent and child tables are the same.   From the table level, specify referential integrity using the foreign_key_clause with the table_constraint syntax. This syntax allows you to specify a composite foreign key, which is made up of a combination of columns. From the column level, use the REFERENCES clause of the column_constraint syntax to specify a referential integrity constraint in which the foreign key is made up of a single column.   You can designate the same column or combination of columns as both a foreign key and a primary or unique key. You can define multiple foreign keys in a table. Also, a single column can be part of more than one foreign key.   Restrictions: The referenced UNIQUE or PRIMARY key constraint on the parent table must already be defined. The child and parent tables must be on the same database. You cannot define a referential integrity constraint in a CREATE TABLE statement that contains an AS subquery clause. Instead, you must create the table without the constraint and then add it later with an ALTER TABLE statement.
   	foreign_key_clause		designates a column or combination of columns as the foreign key from the table level. You must use this syntax to define a composite foreign key. To satisfy a referential integrity constraint involving composite keys, either the values of the foreign key columns must match the values of the referenced key columns in a row in the parent table, or the value of at least one of the columns of the foreign key must be null.   A composite foreign key must refer to a composite unique key or a composite primary key.
   	REFERENCES		designates the current column or attribute as the foreign key and identifies the parent table and the column or combination of columns that make up the referenced key. If you identify only the parent table and omit the column names, the foreign key automatically references the primary key of the parent table. The corresponding columns of the referenced key and the foreign key must match in number and datatypes.
   	ON DELETE		determines how Oracle automatically maintains referential integrity if you remove a referenced primary or unique key value. If you omit this clause, Oracle does not allow you to delete referenced key values in the parent table that have dependent rows in the child table.   CASCADE specifies that Oracle removes dependent foreign key values. SET NULL specifies that Oracle converts dependent foreign key values to NULL.
   CHECK	specifies a condition that each row in the table must satisfy. To satisfy the constraint, each row in the table must make the condition either TRUE or unknown (due to a null). When Oracle evaluates a CHECK constraint condition for a particular row, any column names in the condition refer to the column values in that row. If you create multiple CHECK constraints for a column, design them carefully so their purposes do not conflict. Oracle does not verify that CHECK conditions are not mutually exclusive.   The condition of a CHECK constraint can refer to any column in the table, but it cannot refer to columns of other tables.

1. Lab tasks

Create the following tables with integrity constraints.

NOTE. Our database has so cold recursive integrity constraint definitions/ It means the following: The TEACHER table references to the DEPARTMENT table and DEPARTMENT table references to the FACULTY table/ Ay the same time TEACHER and DEPARTMENT tables reference to the TEACHER table. That is why these tables are defined in such a way:

1) First of all the FACULTY and DEPARTMENT tables are defined. And at the same time the columns DeanFK HeadFK (it foreign keys))are defined without TEREFENCES clause

2) The table TEACHER is defined with all references keys

3) At last with the help of ALTER TABLE statement the REFERENCES close is defined for columns DeanFK and HeadFK

NOTE. In terms of ER-modelling language our database has the following structure

Table name	Column name	Column data type	Length (preci­sion)	Scale	Column constraint
FACULTY	FacPK	integer			PRIMARY KEY
	Name	varchar2	50		UNIQUE, cannot be NULL
	DeanFK	integer			Dean of the faculty. It is a foreign key references to the TchPK column in the TEACHER table. If the dean is deleted from TEACHER table than the reference is set to NULL
	Building	char	5		Building of the faculty. Takes the values: ’1’, ’2’, ’3’, ’4’, ’5’, ’6’, ’7’, ’8’, ’9’, ’10’
	Fund	number	9	2	fund cannot be less than 100000
table constraint
DEPARTMENT	DepPK	integer			PRIMARY KEY
	FacFK	integer			FOREIGN KEY referenced to FacPK of the FACULTY. It is not possible to delete faculty if it has at least one department.
	Name	varchar2	50		Department name. Cannot be NULL
	HeadFK	integer			Head of the department. It is a foreign key references to the TchPK column in the TEACHER table. If the head is deleted from TEACHER table then the reference is set to NULL
	Building	char	5		Building of the department. Takes the values: ’1’, ’2’, ’3’, ’4’, ’5’, ’6’, ’7’, ’8’, ’9’, ’10’
	Fund	number	8	2	Fund take the values in the interval 20000.00- 100000
table constraints	pair of columns (FacFK,name)is UNIQUE (that is the faculty cannot have different departments with identical names)
TEACHER	TchPK	integer			PRIMARY KEY
	DepFR	integer			FOREIGN KEY referenced to DepNo of DEPARTMENT. If referenced department is deleted the key set to NULL.
	Name	varchar2	50		Name of the teacher, cannot be NULL
	Post	varchar2	20		Post of the teacher. Take the values from the list: assistant, counselor, assistant professor, professor
	Tel	char	7
	Hiredate	date			Hire date. should be more than 01.01.1950; cannot be NULL
	Salary	number	6	2	Must be more than 1000, cannot be NULL
	Commission	number	6	2	cannot be negative. DEFAULT value is 0
	ChiefFK	Integer			Chief of the teacher. It is the foreign key that references to the primary key TchPK of the TEACHER table. If a teacher is deleted all references to it is set to NULL
table constraint	a) Commission should be at least twice less than salary b) Salary + Commission is in interval 1000-3000 c) ChiefFK cannot be equal to TchPK (that is teacher cannot be chief of of himself)
SGROUP	GrpPK	integer			PRIMARY KEY
	DepFK	integer			FOREIGN KEY referenced to DepPK of DEPARTMENT. If referenced department is deleted the key set to NULL.
	Course	number	1		take the values from the list: 1, 2, 3, 4, 5, 6
	Num	number	3		Group numbe. Takes the values in the interval 0-700
	Quantity	number	2		Number of students in the group/ Take the value in the interval 1 - 50
	Curator	integer			FOREIGN KEY referenced to TchPK of TEACHER. If referenced department is deleted the key set to NULL.
	Rating	number	3		take the values in the interval 0 – 100. DEFAULT value is 0.
table constraints	Pair of values (DepFK, Num) is UNIQUE (that is any department cannot have groups with identical numbers) Pair of foreign keys (DepFK, Curator) is UNIQUE. That is any teacher may be curator in only one group in any department.
SUBJECT	SbjPK	integer			PRIMARY KEY
	Name	varchar2	50		cannot be NULL
table constraint
ROOM	RomPK	integer			PRIMARY KEY
	Num	number	4		Room number, cannot be NULL
	Seats	number	3		Number seats in the room, is in interval 1 - 300
	Floor	number	2		Floor of the room, is in interval 1 – 16
	Building	char	5		Building of the room/ cannot be NULL. Take values from the following list: ’1’, ’2’, ’3’, ’4’, ’5’, ’6’, ’7’, ’8’, ’9’, ’10’
table constraint	pair of values (Num, Building) is UNIQUE
LECTURE	TchFK	integer			FOREIGN KEY references to TchPK of TEACHER. If references teacher is deleted the key is set to NULL.
	GrpFK	integer			FOREIGN KEY references to GrpPK of SGROUP. If referenced group is deleted the corresponding lecture is deleted too (cascade deletion).
	SbjFK	integer			FOREIGN KEY references to SbjNo of SUBJECT. It is not possible to delete subject if there exists at least one lecture that is referenced to this subject.
	RomNo	integer			FOREIGN KEY referenced to RomNo of ROOM. If referenced room is deleted the key set to NULL.
	Type	varchar2	25		Type of the lecture. Take the values from the list: lecture, lab, seminar, practice. Cannot be NULL
	Day	char	3		Day of the week. Take the values from the list: sun, mon, tue, wed, thu, fri, sat. Cannot be NULL
	Week	number	1		Week of the lesson Take the values 1 or 2. Cannot be NULL
	Lesson	number	1		Take the values in the interval 1 – 8. Cannot be NULL
table constraint	Values of columns (GrpFK, Day, Week, Lesson) is UNIQUE. That is one group cannot has two or more different lectures in the same lesson, day and week. Values of columns (TchFK, Day, Week, Lesson) is UNIQUE. That is the same condition is true for any teacher