Date post: 2017-10-04 15:03
DISABLE Clause Specify DISABLE to disable the integrity constraint. Disabled integrity constraints appear in the data dictionary along with enabled constraints. If you do not specify this clause when creating a constraint, Oracle automatically enables the constraint.
A primary key constraint designates a column as the primary key of a table or view. A composite primary key designates a combination of columns as the primary key. When you define a primary key constraint inline, you need only the PRIMARY KEY keywords. When you define a primary key constraint out of line, you must also specify one or more columns. You must define a composite primary key out of line.
Because of the first ON DELETE clause, if manager number 7887 is deleted from the employees table, then Oracle sets to null the value of manager_id for all employees in the dept_75 table who previously had manager 7887.
For example, in market research , the null hypothesis would be "A ten-percent increase in price will not adversely affect the sale of this product." Based on survey results, this hypothesis will be either accepted as correct or rejected as incorrect.
In the current article we show the very simple hash table example. It uses simple hash function, collisions are resolved using linear probing (open addressing strategy) and hash table has constant size. This example clearly shows the basics of hashing technique.
You would then use CSS to position the " (PDF)" text (the span class= pdficon element) off-screen. See CSS in Action: Invisible Content Just for Screen Reader Users for more details. Sighted users would see the PDF background image and screen reader users would hear the off-screen " (PDF)" text.
The constraint fk_empid_hiredate ensures that all the employees in the dept_75 table have employee_id and hire_date combinations that exist in the employees table. Before you define and enable this constraint, you must define and enable a constraint that designates the combination of the employee_id and hire_date columns of the employees table as a primary or unique key.
In this painting, the artist Emanuel Leutze used light, color, form, perspective, proportion, and motion to create the composition.
CONSTRAINT constraint_name Specify a name for the constraint. If you omit this identifier, then Oracle Database generates a name with the form SYS_C n . Oracle stores the name and the definition of the integrity constraint in the USER_ , ALL_ , and DBA_CONSTRAINTS data dictionary views (in the CONSTRAINT_NAME and SEARCH_CONDITION columns, respectively).
Based upon these rules, Option D ( alt="George Washington" ) would likely be the best alternative text in this instance. Option A unnecessarily describes the image as an image. Option B provides extra information that is not presented directly in the image and it is also redundant with content presented later within the text. Option C (no alt attribute) is not appropriate because the image conveys content that is not directly presented in the surrounding context. Even though the surrounding text does indicate that it's referring to George Washington, visual users can tell this directly from the content of the image - so if the image conveys content, it should be given alternative text.