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This Oracle tutorial explains how to create, drop, disable, and enable a primary key in Oracle with syntax and examples.

What is a primary key in Oracle?

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To create a primary key in a table, you use the PRIMARY KEY constraint. Oracle PRIMARY KEY constraint examples. Typically, you create a primary key for a table when you create that table. In addition, you can add a primary key to a table after the fact by using the ALTER TABLE statement. Creating a primary key that consists of one column. Jul 01, 2010 We need to generate a sequence of numbers using a sql statement. This will generate a number sequence. Nothing fancy, simplest of sql known:) Here it is: SELECT ROWNUM FROM DUAL CONNECT BY LEVEL generate the random data, the oracle build in package “dbmsrandom” comes handy.

In Oracle, a primary key is a single field or combination of fields that uniquely defines a record. None of the fields that are part of the primary key can contain a null value. A table can have only one primary key.

Note

• In Oracle, a primary key can not contain more than 32 columns.
• A primary key can be defined in either a CREATE TABLE statement or an ALTER TABLE statement.

Create Primary Key - Using CREATE TABLE statement

You can create a primary key in Oracle with the CREATE TABLE statement.

Syntax

The syntax to create a primary key using the CREATE TABLE statement in Oracle/PLSQL is:

Example

Let's look at an example of how to create a primary key using the CREATE TABLE statement in Oracle:

In this example, we've created a primary key on the supplier table called supplier_pk. It consists of only one field - the supplier_id field.

We could also create a primary key with more than one field as in the example below:

Create Primary Key - Using ALTER TABLE statement

You can create a primary key in Oracle with the ALTER TABLE statement.

Syntax

The syntax to create a primary key using the ALTER TABLE statement in Oracle/PLSQL is:

Example

Let's look at an example of how to create a primary key using the ALTER TABLE statement in Oracle.

In this example, we've created a primary key on the existing supplier table called supplier_pk. It consists of the field called supplier_id.

We could also create a primary key with more than one field as in the example below:

Drop Primary Key

You can drop a primary key in Oracle using the ALTER TABLE statement.

Syntax

The syntax to drop a primary key using the ALTER TABLE statement in Oracle/PLSQL is:

Example

Let's look at an example of how to drop a primary key using the ALTER TABLE statement in Oracle. ard mediathek film download mac

In this example, we're dropping a primary key on the supplier table called supplier_pk.

Disable Primary Key

You can disable a primary key in Oracle using the ALTER TABLE statement.

Syntax

The syntax to disable a primary key using the ALTER TABLE statement in Oracle/PLSQL is:

Example

Let's look at an example of how to disable a primary using the ALTER TABLE statement in Oracle.

In this example, we're disabling a primary key on the supplier table called supplier_pk.

Enable Primary Key

You can enable a primary key in Oracle using the ALTER TABLE statement.

Syntax

The syntax to enable a primary key using the ALTER TABLE statement in Oracle/PLSQL is:

Example

Let's look at an example of how to enable a primary key using the ALTER TABLE statement in Oracle.

In this example, we're enabling a primary key on the supplier table called supplier_pk.

The DBMS_RANDOM package provides a built-in random number generator.

This chapter contains the following topics:

• • Operational notes

Note:

DBMS_RANDOM is not intended for cryptography.

Using DBMS_RANDOM

Operational notes

• The RANDOM function produces integers in the range [-2^^31, 2^^31).

• The VALUE function produces numbers in the range [0,1) with 38 digits of precision.

DBMS_RANDOM can be explicitly initialized but does not require initialization before a call to the random number generator. It automatically initializes with the date, user ID, and process ID if no explicit initialization is performed.

If this package is seeded twice with the same seed, then accessed in the same way, it produces the same result in both cases.

In some cases, such as when testing, you may want the sequence of random numbers to be the same on every run. In that case, you seed the generator with a constant value by calling an overload of SEED. To produce different output for every run, simply omit the seed call. Then the system chooses a suitable seed for you.

Summary of DBMS_RANDOM subprograms

Table 6-1 DBMS_RANDOM package subprograms

Subprogram	Description
Initializes the package with a seed value.
Returns random numbers in a normal distribution.
Generates a random number.
Resets the seed.
Gets a random string.
Terminates package.
One version gets a random number greater than or equal to 0 and less than 1, with 38 digits to the right of the decimal point (38-digit precision). The other version gets a random Oracle Database number x, where x is greater than or equal to a specified lower limit and less than a specified higher limit.

Note:

The INITIALIZE procedure, RANDOM function and TERMINATE procedure are deprecated. They are included in this release for legacy reasons only.

Notes:

• The PLS_INTEGER and BINARY_INTEGER data types are identical. This document uses BINARY_INTEGER to indicate data types in reference information (such as for table types, record types, subprogram parameters, or subprogram return values), but may use either in discussion and examples.

• The INTEGER and NUMBER(38) data types are also identical. This document uses INTEGER throughout.

INITIALIZE procedure

This procedure is deprecated. Although currently supported, it should not be used. It initializes the random number generator.

Parameters

Table 6-2 INITIALIZE procedure parameters

Parameter	Description
val	Seed number used to generate a random number

Usage notes

This procedure is obsolete as it simply calls the SEED procedure.

NORMAL function

This function returns random numbers in a standard normal distribution.

Return value

The random number, a NUMBER value

RANDOM function

Oracle Random Function

This procedure is deprecated. Although currently supported, it should not be used. It generates and returns a random number.

Return value

A random BINARY_INTEGER value greater than or equal to -power(2,31) and less than power(2,31)

Usage notes

See the NORMAL function and the VALUE function.

SEED procedure

This procedure resets the seed used in generating a random number.

Parameters

Table 6-3 SEED procedure parameters

Parameter	Description
val	Seed number or string used to generate a random number

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Usage notes

The seed can be a string up to length 2000.

STRING function

This function generates and returns a random string.

Parameters

Table 6-4 STRING function parameters

Parameter	Description
opt	What the returning string looks like: 'u', 'U' - Returning string is in uppercase alpha characters. 'l', 'L' - Returning string is in lowercase alpha characters. 'a', 'A' - Returning string is in mixed-case alpha characters. 'x', 'X' - Returning string is in uppercase alpha-numeric characters. 'p', 'P' - Returning string is in any printable characters. Otherwise the returning string is in uppercase alpha characters.
len	Length of the returned string

Return value

Oracle Random Number Example

A VARCHAR2 value with the random string

TERMINATE procedure

This procedure is deprecated. Although currently supported, it should not be used. It would be called when the user is finished with the package.

VALUE function

One version returns a random number, greater than or equal to 0 and less than 1, with 38 digits to the right of the decimal (38-digit precision). The other version returns a random Oracle Database NUMBER value x, where x is greater than or equal to the specified low value and less than the specified high value.

Parameters

Table 6-5 VALUE function parameters

Parameter	Description
low	Lower limit of the range in which to generate a random number
high	Upper limit of the range in which to generate a random number

Oracle Random Row

Return value

Generate Random Key In Oracle Software

A NUMBER value that is the generated random number Asa generate ssh key asdm.