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How much space did a slave on the middle passage have?
Slaves on the Middle Passage were typically allocated between 4 to 6 feet of space in the ship's hold, with very cramped and unsanitary conditions. They were heavily crowded together, laying in rows on hard surfaces, with limited access to ventilation and light. This inhumane treatment contributed to high mortality rates during the transatlantic voyage.
What is the chemistry periodical table?
It is the biggest type of law in america. No one can withdraw from this law on the punishment of death. If you do happen to dissobey this law you can say to police officers who catch you the secret word (Higgoby) this secret word if changed every 2 minutes so be quick.
List out Codd's rules for Relational Databases?
The rulesRule 0: The system must qualify as relational, as a database, and as a management system.For a system to qualify as a relational database management system (RDBMS), that system must use its relational facilities (exclusively) to manage the database. Rule 1: The information rule:All information in the database is to be represented in one and only one way, namely by values in column positions within rows of tables.Rule 2: The guaranteed access rule:All data must be accessible. This rule is essentially a restatement of the fundamental requirement for primary keys. It says that every individual scalar value in the database must be logically addressable by specifying the name of the containing table, the name of the containing column and the primary key value of the containing row.Rule 3: Systematic treatment of null values:The DBMS must allow each field to remain null (or empty). Specifically, it must support a representation of "missing information and inapplicable information" that is systematic, distinct from all regular values (for example, "distinct from zero or any other number", in the case of numeric values), and independent of data type. It is also implied that such representations must be manipulated by the DBMS in a systematic way.Rule 4: Active online catalog based on the relational model:The system must support an online, inline, relational catalog that is accessible to authorized users by means of their regular query language. That is, users must be able to access the database's structure (catalog) using the same query language that they use to access the database's data.Rule 5: The comprehensive data sublanguage rule:The system must support at least one relational language thatHas a linear syntaxCan be used both interactively and within application programs,Supports data definition operations (including view definitions), data manipulation operations (update as well as retrieval), security and integrity constraints, and transaction management operations (begin, commit, and rollback).Rule 6: The view updating rule:All views that are theoretically updatable must be updatable by the system.Rule 7: High-level insert, update, and delete:The system must support set-at-a-time insert, update, and delete operators. This means that data can be retrieved from a relational database in sets constructed of data from multiple rows and/or multiple tables. This rule states that insert, update, and delete operations should be supported for any retrievable set rather than just for a single row in a single table.Rule 8: Physical data independence:Changes to the physical level (how the data is stored, whether in arrays or linked lists etc.) must not require a change to an application based on the structure.Rule 9: Logical data independence:Changes to the logical level (tables, columns, rows, and so on) must not require a change to an application based on the structure. Logical data independence is more difficult to achieve than physical data independence.Rule 10: Integrity independence:Integrity constraints must be specified separately from application programs and stored in the catalog. It must be possible to change such constraints as and when appropriate without unnecessarily affecting existing applications.Rule 11: Distribution independence:The distribution of portions of the database to various locations should be invisible to users of the database. Existing applications should continue to operate successfully :when a distributed version of the DBMS is first introduced; andwhen existing distributed data are redistributed around the system.Rule 12: The nonsubversion rule:If the system provides a low-level (record-at-a-time) interface, then that interface cannot be used to subvert the system, for example, bypassing a relational security or integrity constraint.
Code rule of dbms to rdbms?
Codd's twelve rules are a set of thirteen rules (numbered zero to twelve) proposed by Edgar F. Codd, a pioneer of the relational model fordatabases, designed to define what is required from a database management system in order for it to be considered relational, i.e., a relational database management system (RDBMS).[1][2] They are sometimes jokingly referred to as "Codd's Twelve Commandments".The relational DBMS model is based on the relational algebra devised by E.F.CODD.The relational algebra by Codd is done through 12 rules popularly known as CODD's 12 Rules.(1)Information Rule:All information in a relational database including table names column names arerepresented explicitly by values in tables.Knowledge of only one language is necessary toaccess all data such as description of the table and attribute definitions integrityconstraints action to be taken when constraints are voilated and security information.(2)Guaranted Access Rule:Every pieceof data in the relational database can be accessed by using acombination of a table name a primary key value that identifies the row and a columnthat identifies the cell.The benefit of this is that user productivity is improvedsince there is no need to resort to using physical pointers addresses.Providesdata independence.(3)Systematic treatment of Nulls Rule:The RDBMS handles that have unknown on inapplicable values in a predefined fashion.RDBMS distinguishes between zeros blanks and nulls in records and handles such values ina consistent manner that produces correct answers comparisions and calculations.(4)Active On-Line Catalog Based on the Relational Model.THe description of a database and its contents are database tables and thereforecan be queries online via the data language.The DBA's productivity is improved sincechanges and additionsto the catalog can be done with the same commands that areused to access any other table.All queries and reports can be done as with other tables.(5)Comprehensive Data Sublanguage Rule:A RDBMS may support several languages but atleast one of them allows the user to do allof the following:define tables view query and update data set integrity constraintsset authorization and define transactions.(6)View Updating Rule:Any view that is theoretically updatable if changes can be made to the tables thateffect the desired changes in the view.Data consistency is ensured since changesin the underlying tables are transmittedto the view they support.Logical dataindependence reduces maintenance cost.(7)High Level Inserts Update and Delete:THe RDBMS supports insertion updation and deletion at a table level.With this theRDBMS can improveperformance by optimizing the path to be taken to execute the actionEase of use improved since commands act on set of records.(8)Physical data Independence :The execution of adhoc requests and application programs is not affected by changesin the physical data access and storage methods.Database administrators can makethe changes to physical acccess and storage methods which improve performancebut do not changes in the application programs or adhoc requests.This reducesmaintenance costs.(9)Logical data Independence:Logical changes in tables and view such asadding/deleting columns or changingfield lenghts do not necessitate modifications in application programs or in theformat of adhoc requests.(10)Integrity Independance:Like table/view definitions integrity constraints are atored in theon-line catalog and therefore can be changed without necessitating changesin application programs or in the format of adhoc requests .The following two integrity constraints must be supported.(a)Entity Integrity:No component of primary key is allowed to have anull value.(b)Referential integrity:For each distinct non-null foreign key value in a relationaldatabasethere must exist a matching primary key from the same range of data value.(11)Distribution Independence:Application programs and adhoc requests are not affected by changesin the distribution of the physical data.(12)Nonsubversion Rule:If the RDBMS has a language change that accesses the informationof a record at a time this language cannot be used to by-pass theintegrity constraints.Inoreder to adhere to this rule the RDBMS must have anactive catalog that containsthe constraints must have a logical data independence.
What is the difference between union and intersect operations in SQL?
* The UNION operator combines the output of two query expressions into a single result set. Query expressions are executed independently, and their output is combined into a single result table. * The EXCEPT operator evaluates the output of two query expressions and returns the difference between the results. The result set contains all rows returned from the first query expression except those rows that are also returned from the second query expression. * The INTERSECT operator evaluates the output of two query expressions and returns only the rows common to each.
What clause returns only one copy of each set of duplicate rows selected?
Using the DISTINCT keyword in the SELECT clause ensures that only one copy of each set of duplicate rows selected is returned. This keyword filters out duplicate rows from the result set based on all selected columns.
How are all rows in a table selected?
All rows & columns in a table can be selected by using the below query Select * from table_name If you do not have any where condition in the query then all rows will be selected.
Which is more important in a sql query IN or EXISTS?
EXISTS is more efficient that IN , Because EXISTS use indexes of the table and hence scans the table faster, as well as it returns the boolean value (T or F), If T is received for EXISTS clause than the rows will be returned otherwise not. where as IN works as simple query where it will scan all possible values in the table and than compares the condition given by you and then the result.
What basic clause in an SQL statement is used to retrieve rows and columns from tables?
The SELECT clause is used to retrieve rows and columns from tables. Ex: Select * from employee
How do you set up ascending and descending order in a table and a query?
I'm actually not familiar with Access, but I'll try to help. Usually the primary key will physically order the rows in a database table. In SQL-query you can use "order by" clause. The default order is usually ascending. You can also add "asc" or "desc" after the column name. Please do notice, primary keys are not for ordering rows. You should really let the database decide how to save the rows. You should always order the rows in your query (if needed), not modify or trust the physical order! select col1 from foo order by col2 select col1 from foo order by col2 desc, col3 asc
What two options do you use with the on commit clause when creating a global temporary table?
When creating a global temporary table, you can specify either "preserve rows" or "delete rows" with the ON COMMIT clause. "Preserve rows" keeps the data in the table after a commit, while "delete rows" removes the data in the table after a commit.
What is Criteria of the Query?
You apply criteria to queries using the WHERE clause. ex: Select * from tbl_emp This query would fetch all rows from the table tbl_emp Select * from tbl_emp where emp_name = "Rocky" This query would fetch all rows from the table that have employee name as Rocky
Do you have a table without rows?
You can have a table without rows. It would be an empty table with no data. select (*)count from TABLENAME; 0 rows returned.
What links two tables using a common field in both tables and extracts the relevant data from each?
A join operation links two tables using a common field and extracts relevant data. By specifying the common field in the ON clause of a SQL query, the database can combine rows from both tables based on matching values in that field. This allows data to be retrieved from multiple tables in a single query.
Where clause restricts rows prior to inclusion in a group calculation?
TRUE
What impact does normalization have on writing queries?
The most important thing about normalization of tables in a database for the purposes of query writing is to allow only the data wanted to be returned and you don't end up with what is called a Cartesian product... where it is possible that all rows are returned in error because the keys from table to table are not normalized correctly.
