SQL_CONSTRAINTS

8/7/2019 SQL_CONSTRAINTS

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The TOP option is used for limiting the output of a query result set. TOP can

either specify the number of rows to return, or the percentage of rows to return.The ORDER BY clause can be used successfully with the TOP option.

SELECT TOP 10 *FROM employees

SELECT TOP 20 PERCENT *FROM employees

SELECT TOP 10 *

FROM employeesORDER BY Salary DESC

Using TOP and PERCENT

SELECT TOP 1 WITH TIES * FROM EMPORDER BY SAL


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INTO clause creates a new table and inserts rows and columns listed in theSELECT statement into it. INTO clause also inserts existing rows into a newtable.

SELECT EMPNO,ENAME,JOB INTOEMP20 FROM EMPWHERE DEPTNO =10;

INTO CLAUSE


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[ ] (Wildcard - Character(s) to Match)

Matches any single character within the specified range or set

that is specified between the brackets.

SELECT * FROM EMPWHERE SAL LIKE '[0-9][0-9][0-9]'


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[^] (Wildcard - Character(s) Not to Match)

Matches any single character that is not within the range or setspecified between the square brackets.

SELECT * FROM EMP

WHERE ENAME LIKE 'A[^L]%'


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SELECT AVG(SAL),DEPTNOFROM EMPWHERE DEPTNO IN(10,20)GROUP BY ALL DEPTNO

GROUP BY ALL

If you use ALL, the query results include all groups produced by theGROUP BY clause, even if some of the groups have no rows that meetthe search conditions. Without ALL, a SELECT statement that includesGROUP BY does not show groups for which no rows qualify.


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SELECT AVG(SAL),DEPTNO,JOB

FROM EMPGROUP BY DEPTNO ,JOB WITH CUBE

GROUP BY CUBE

CUBE is an aggregate operator that produces a super aggregate row.

In addition to the usual rows provided by the GROUP BY, it alsoprovides the summary of the rows that the GROUP BY clausegenerates.

The Summary row is displayed for every possible combination ofgroups in the result set.

The Summary row displays NULL in the result set


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SQL Insert

The SQL INSERT command allows you to insert arecord into a table in your database.

INSERT INTO Student (Rollno, name, age)

VALUES ( 1, 'Benny', 12)


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SQL Update

The SQL UPDATE statement allows you to update an existingrecord in the database.

The UPDATE command uses a WHERE clause. If you don't use a

WHERE clause, all rows will be updated.

UPDATE student

SET age = 12WHERE rollno = 1


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SQL Delete

The SQL DELETE statement allows you to delete a record from the database.

The DELETE command uses a WHERE clause. If you don't use a WHEREclause, all rows in the table will be deleted.

DELETE FROM Individual

WHERE Rollno = 1


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Data type Range Storage

bigint-2^63 (-9,223,372,036,854,775,808) to2^63-1 (9,223,372,036,854,775,807)

8 Bytes

int -2^31 (-2,147,483,648) to 2^31-1 (2,147,483,647) 4 Bytes

smallint -2^15 (-32,768) to 2^15-1 (32,767) 2 Bytes

tinyint 0 to 255 1 Byte


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numeric (p, s)Fixed-precision and scale-numeric data from10^38+1 through 10^381.

Storage size is 19 bytes.

money

Monetary data values from (

2^63/10000) (

922,337,203,685,477.5808)through 2^631 (922,337,203,685,477.5807)

Storage size is 8 bytes.


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datetime Date and time data from January 1, 1753, to December 31, 9999,

smalldatetime January 1, 1900, through June 6, 2079


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char [ ( n ) ]Fixed-length, non-Unicode character data with a length of nbytes. n

must be a value from 1 through 8,000.

varchar [ ( n | max ) ]Variable-length, non-Unicode character data. ncan be a value from 1through 8,000.

text Variable-length with a maximum length of 2^31-1 (2,147,483,647)characters.


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national character(n)

Synonym: nchar(n)

Fixed-length Unicode data with a maximum length of 4000 characters.

national character

varying(n)

Synonym: nvarchar(n)

Variable-length Unicode data with a length of 1 to 4000 characters.


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ntext

Variable-length Unicode data with a maximum length of (2^302)/2

(536,870,911) characters.

binary(n) Fixed-length binary data with a maximum length of 8000 bytes.

varbinary(n) Variable-length binary data with a maximum length of 8000 bytes.

image

Variable-length binary data with a maximum length of 2^301

(1,073,741,823) bytes.

Storage is the length of the value in bytes.

uniqueidentifier A globally unique identifier (GUID). Storage size is 16 bytes.


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IDENTITY [(s, i)]

Only data columns of the integer data types can be used for identity columns. A table canhave only one identity column. A seed and increment can be specified and the columncannot be updated.s (seed) = starting valuei (increment) = increment value

ROWGUIDCOLThis is a property of a data column, not a distinct data type. It is a column in a table that isdefined by using the uniqueidentifier data type. A table can have only one ROWGUIDCOLcolumn.


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Using the IDENTITY property with CREATE TABLE

IDENTITY property for an automatically incrementing identification number.

CREATE TABLE employees ( id_num int IDENTITY(1,1),fname varchar (20), lname varchar(30) )

INSERT employees (fname, lname) VALUES ('Karin, 'Josephs')


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Naming Conventions

Must begin with a letter

Can be 130 characters long

Must contain only AZ, az, 09 , _ Must not duplicate the name of another

object owned by the same user

Must not be an reserved word


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The CREATE TABLE Statement

You specify: Table name

Column name, column datatype, and columnsize

CREATE TABLE [schema.]table

(column datatype [DEFAULT expr];


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The DEFAULT Option

Specify a default value for a column duringan insert.

job varchar(15) DEFAULT clerk,


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Creating Tables

SQL> CREATE TABLE dept

2 (deptno NUMBER(2),

3 dname VARCHAR(14),

4 loc VARCHAR(13));

Table created.

Create the table.


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The ALTER TABLE Statement

Use the ALTER TABLE statement to: Add a new column

Modify an existing column

Define a default value for the new columnALTER TABLE table

ADD (column datatype [DEFAULT expr];

ALTER TABLE table

ALTER COLUMN(column_name datatype [DEFAULT expr]);


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Adding a Column

DEPT30

EMPNO ENAME ANNSAL HIREDATE------ ---------- --------

7698 BLAKE 34200 01-MAY-81

7654 MARTIN 15000 28-SEP-817499 ALLEN 19200 20-FEB-81

7844 TURNER 18000 08-SEP-81...

add a

newcolumnintoDEPT30table

DEPT30

EMPNO ENAME ANNSAL HIREDATE

------ ---------- --------

7698 BLAKE 34200 01-MAY-817654 MARTIN 15000 28-SEP-817499 ALLEN 19200 20-FEB-81

7844 TURNER 18000 08-SEP-81...

JOB

JOB

New column


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Adding a Column

You use the ADD clause to add columns.

EMPNO ENAME ANNSAL HIREDATE JOB

--------- ---------- --------- --------- ----

7698 BLAKE 34200 01-MAY-81

7654 MARTIN 15000 28-SEP-817499 ALLEN 19200 20-FEB-81

7844 TURNER 18000 08-SEP-81

...

6 rows selected.

SQL> ALTER TABLE dept30

2 ADD (job VARCHAR(9));

Table altered.

The new column becomes the last column.


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Modifying a Column

You can change a column's datatype,size, and default value.

A change to the default value affects

only subsequent insertions to the table.

ALTER TABLE dept30

ALTER COLUMN (ename VARCHAR(15));

Table altered.


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Dropping a Table

All data and structure in the table isdeleted.

Any pending transactions are committed.

All indexes are dropped.

You cannot roll back this statement.

SQL> DROP TABLE dept30;

Table dropped.


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Truncating a Table

The TRUNCATE TABLE statement: Removes all rows from a table

Releases the storage space used by thattable

Cannot roll back row removal whenusing TRUNCATE

Alternatively, remove rows by using theDELETE statement

SQL> TRUNCATE TABLE department;

Table truncated.


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What Are Constraints?

Constraints enforce rules at the table level. Constraints prevent the deletion of a table if

there are dependencies.

The following constraint types are :- NOT NULL

UNIQUE Key

PRIMARY KEY

FOREIGN KEY CHECK


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Constraint Guidelines

Create a constraint: At the same time as the table is created

After the table has been created

Define a constraint at the column or tablelevel.


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Defining Constraints

CREATE TABLE [schema.]table

(column datatype [DEFAULT expr]

[column_constraint],

[table_constraint]);

CREATE TABLE emp(

empno NUMBER(4),

ename VARCHAR(10),

deptno NUMBER(7,2) NOT NULL,CONSTRAINT emp_empno_pk

PRIMARY KEY (EMPNO));


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The NOT NULL Constraint

Ensures that null values are notpermitted for the column

EMP

EMPNO ENAME JOB ... COMM DEPTNO

7839 KING PRESIDENT 10

7698 BLAKE MANAGER 307782 CLARK MANAGER 10

7566 JONES MANAGER 20...

NOT NULL constraint(no row may containa null value forthis column)

Absence of NOT NULLconstraint(any row can containnull for this column)

NOT NULL constraint


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The NOT NULL Constraint

Defined at the column level

SQL> CREATE TABLE emp(

2 empno NUMBER(4),

3 ename VARCHAR(10) NOT NULL,

4 job VARCHAR(9),5 mgr NUMBER(4),

6 hiredate DATE,

7 sal NUMBER(7,2),

8 comm NUMBER(7,2),

9 deptno NUMBER(7,2) NOT NULL);


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The UNIQUE Key Constraint

DEPT

DEPTNO DNAME LOC

------ ---------- --------

10 ACCOUNTING NEW YORK20 RESEARCH DALLAS

30 SALES CHICAGO40 OPERATIONS BOSTON

UNIQUE key constraint

50 SALES DETROIT

60 BOSTON

Insert into Not allowed(DNAME SALES

already exists)

Allowed


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The PRIMARY KEY Constraint

DEPT

DEPTNO DNAME LOC

------ ---------- --------

10 ACCOUNTING NEW YORK20 RESEARCH DALLAS

30 SALES CHICAGO40 OPERATIONS BOSTON

PRIMARY KEY

Insert into

20 MARKETING DALLAS

FINANCE NEW YORK

Not allowed(DEPTNO 20 alreadyexists)

Not allowed(DEPTNO is null)


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The PRIMARY KEY Constraint

Defined at either the table level or thecolumn level

SQL> CREATE TABLE dept(

2 deptno NUMBER(2),3 dname VARCHAR(14),

4 loc VARCHAR(13),

5 CONSTRAINT dept_dname_uk UNIQUE (dname),

6 CONSTRAINT dept_deptno_pk PRIMARY KEY(deptno));


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The FOREIGN KEY Constraint

DEPT

DEPTNO DNAME LOC------ ---------- --------

10 ACCOUNTING NEW YORK

20 RESEARCH DALLAS...

PRIMARYKEY

EMPEMPNO ENAME JOB ... COMM DEPTNO

7839 KING PRESIDENT 107698 BLAKE MANAGER 30

...

FOREIGNKEY

7571 FORD MANAGER ... 200 9

7571 FORD MANAGER ... 200

Insert into

Not allowed

(DEPTNO 9does not exist inthe DEPT table

Allowed


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Adding a Constraint

Add a FOREIGN KEY constraint to theEMP table indicating that a managermust already exist as a valid employee

in the EMP table.SQL> ALTER TABLE emp2 ADD CONSTRAINT emp_mgr_fk

3 FOREIGN KEY(mgr) REFERENCES emp(empno);

Table altered.


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Dropping a Constraint

Remove the manager constraint fromthe EMP table.

SQL> ALTER TABLE emp

2 DROP CONSTRAINT emp_mgr_fk;

Table altered.

SQL_CONSTRAINTS

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