Fundamentals of Database Systems
... relational algebra expression. It represents the input relations of the query as leaf nodes of the tree, and represents the relational algebra operations as internal nodes. An execution of the query tree consists of executing an internal node operation whenever its operands are available and then re ...
... relational algebra expression. It represents the input relations of the query as leaf nodes of the tree, and represents the relational algebra operations as internal nodes. An execution of the query tree consists of executing an internal node operation whenever its operands are available and then re ...
Lecture 7 part 1
... Example COMPANY Database (continued) – We store each EMPLOYEE's social security number, address, salary, sex, and birth date. Each employee works for one department but may work on several projects. We keep track of the number of hours per week that an employee currently works on each project. We a ...
... Example COMPANY Database (continued) – We store each EMPLOYEE's social security number, address, salary, sex, and birth date. Each employee works for one department but may work on several projects. We keep track of the number of hours per week that an employee currently works on each project. We a ...
Lecture 8 - e-learning website
... • The presence of a multivalued dependency means that if versions 1 and 2 are implemented, the tables are likely to contain quite a few null values; in fact, the tables do not even have a viable candidate key. (The EMP_NUM values are not unique, so they cannot be PKs. No combination of the attribute ...
... • The presence of a multivalued dependency means that if versions 1 and 2 are implemented, the tables are likely to contain quite a few null values; in fact, the tables do not even have a viable candidate key. (The EMP_NUM values are not unique, so they cannot be PKs. No combination of the attribute ...
ppt
... The warehouse is used by analysts to predict trends and move goods to where they are selling best. ...
... The warehouse is used by analysts to predict trends and move goods to where they are selling best. ...
Relational Database Schemes and SAS Software SQL Solutions
... dimension. As a result, the programmer has to guess whether subjctID has unique values, in which case a subject can have only one nameaddress, or duplicate values, so that different addresses for the same subject become possible but not formally distinguishable from two rows with the same subjctID, ...
... dimension. As a result, the programmer has to guess whether subjctID has unique values, in which case a subject can have only one nameaddress, or duplicate values, so that different addresses for the same subject become possible but not formally distinguishable from two rows with the same subjctID, ...
Database Tables
... Changing primary key values once we store the data in tables is a complicated matter because the primary key can appear as a foreign key in many other tables. Incidentally, surrogate keys are almost always less likely to change compared with natural keys. Choose the simplest candidate. The one that ...
... Changing primary key values once we store the data in tables is a complicated matter because the primary key can appear as a foreign key in many other tables. Incidentally, surrogate keys are almost always less likely to change compared with natural keys. Choose the simplest candidate. The one that ...
Chapter15 - Computer Science
... • Creating a new copy each time is essential – If it were to be created once and then stored on the user’s computer, then there would be two copies of the information ...
... • Creating a new copy each time is essential – If it were to be created once and then stored on the user’s computer, then there would be two copies of the information ...
The Relational Model
... Also delete all Enrolled tuples that refer to it. Disallow deletion of a Students tuple that is referred to. Set sid in Enrolled tuples that refer to it to a default sid. (In SQL, also: Set sid in Enrolled tuples that refer to it to a special value null, denoting `unknown’ or `inapplicable’.) ...
... Also delete all Enrolled tuples that refer to it. Disallow deletion of a Students tuple that is referred to. Set sid in Enrolled tuples that refer to it to a default sid. (In SQL, also: Set sid in Enrolled tuples that refer to it to a special value null, denoting `unknown’ or `inapplicable’.) ...
Chapter 3 - La Salle University
... – Multiple occurrences of values in a table are not redundant when they are required to make the relationship work – Redundancy exists only when there is unnecessary duplication of attribute values ...
... – Multiple occurrences of values in a table are not redundant when they are required to make the relationship work – Redundancy exists only when there is unnecessary duplication of attribute values ...
Download-5 LOGICAL 5tcss545A_8
... • Referential Integrity – An integrity constraint specifying that the value (or existence) of an attribute in one relation depends on the value (or existence) of the same attribute in another relation ...
... • Referential Integrity – An integrity constraint specifying that the value (or existence) of an attribute in one relation depends on the value (or existence) of the same attribute in another relation ...
Relational Databases and SQLite
... • Complexity makes speed possible and allows you to get very fast results as the data size grows • By normalizing the data and linking it with integer keys, the overall amount of data which the relational database must scan is far lower than if the data were simply flattened out • It might seem like ...
... • Complexity makes speed possible and allows you to get very fast results as the data size grows • By normalizing the data and linking it with integer keys, the overall amount of data which the relational database must scan is far lower than if the data were simply flattened out • It might seem like ...
The Relational Model
... Where do ICs Come From? ICs are based upon the semantics of the realworld enterprise that is being described in the database relations. We can check a database instance to see if an IC is violated, but we can NEVER infer that an IC is true by looking at an instance. ...
... Where do ICs Come From? ICs are based upon the semantics of the realworld enterprise that is being described in the database relations. We can check a database instance to see if an IC is violated, but we can NEVER infer that an IC is true by looking at an instance. ...
Database
... making such a change in the foreign key value, but not in the primary key value. This problem could be handled by asserting that primary key values cannot be changed once they are established. In this case, updates to the customer table will be handled in most systems by including an ON UPDATE RESTR ...
... making such a change in the foreign key value, but not in the primary key value. This problem could be handled by asserting that primary key values cannot be changed once they are established. In this case, updates to the customer table will be handled in most systems by including an ON UPDATE RESTR ...
Title
... • Solution: Web Base Management Systems (WBMSs) – 2 challenges 1) querying and extracting structure from semi-structured web data, transforming it, and presenting custom views 2) mapping structured database data to the web (adding navigational access paths, redundancy, ...) ...
... • Solution: Web Base Management Systems (WBMSs) – 2 challenges 1) querying and extracting structure from semi-structured web data, transforming it, and presenting custom views 2) mapping structured database data to the web (adding navigational access paths, redundancy, ...) ...
PPT
... Relational databases introduced by E. F. Codd in the 1970s • Turing Award Winner Relational Database • data stored in tables • relationships among data stored in tables • data can be accessed and viewed in different ways ...
... Relational databases introduced by E. F. Codd in the 1970s • Turing Award Winner Relational Database • data stored in tables • relationships among data stored in tables • data can be accessed and viewed in different ways ...
The Relational Model - Brock Computer Science
... information (or a summary), while hiding details in underlying relation(s). ...
... information (or a summary), while hiding details in underlying relation(s). ...
The SQL Query Language
... SQL provides a special value null for such situations. Special operators needed to check if value is/is not null. Is rating>8 true or false when rating is equal to null? What about AND, OR and NOT connectives? We need a 3-valued logic (true, false and unknown). Meaning of constructs must be defined ...
... SQL provides a special value null for such situations. Special operators needed to check if value is/is not null. Is rating>8 true or false when rating is equal to null? What about AND, OR and NOT connectives? We need a 3-valued logic (true, false and unknown). Meaning of constructs must be defined ...
The Relational Data Model
... • a1 is a foreign key of R1 referring to a2 in R2 => if v is a value of a1, there is a unique tuple of R2 in which a2 has value v – This is a special case of referential integrity: a2 must be a candidate key of R2 (CrsCode is a key of Course) – If no row exists in R2 => violation of referential inte ...
... • a1 is a foreign key of R1 referring to a2 in R2 => if v is a value of a1, there is a unique tuple of R2 in which a2 has value v – This is a special case of referential integrity: a2 must be a candidate key of R2 (CrsCode is a key of Course) – If no row exists in R2 => violation of referential inte ...
