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46-492: UniVerse was originally developed by VMark Software and UniData was originally developed by the Unidata Corporation. Both Universe and Unidata are used for vertical application development and are embedded into the vertical software applications. In 1997, the Unidata Corporation merged with VMark Systems to form Ardent Software. In March 2000, Ardent Software was acquired by Informix . IBM subsequently acquired

92-505: A relation r if and only if r is a function. It is usually required that R and S must have at least one common attribute, but if this constraint is omitted, and R and S have no common attributes, then the natural join becomes exactly the Cartesian product. The natural join can be simulated with Codd's primitives as follows. Let c 1 , ..., c m be the attribute names common to R and S , r 1 , ..., r n be

138-408: A user . Files are similar to tables in a relational database in that each file has a unique name to distinguish it from other files and zero to multiple unique records that are logically related to each other. Files are made of two parts: a data file and a file dictionary (DICT). The data file contains records that store the actual data. The file dictionary may contain metadata to describe

184-722: A change in column names may change the results. In the SQL:2011 standard, natural joins are part of the optional F401, "Extended joined table", package. In many database environments the column names are controlled by an outside vendor, not the query developer. A natural join assumes stability and consistency in column names which can change during vendor mandated version upgrades. The joined table retains each row—even if no other matching row exists. Outer joins subdivide further into left outer joins, right outer joins, and full outer joins, depending on which table's rows are retained: left, right, or both (in this case left and right refer to

230-438: A new column, named the same as another column in the other table. An existing natural join might then "naturally" use the new column for comparisons, making comparisons/matches using different criteria (from different columns) than before. Thus an existing query could produce different results, even though the data in the tables have not been changed, but only augmented. The use of column names to automatically determine table links

276-604: A record in the EMPLOYEE file with 123-45-6789 as the Record ID, JOHN JONES as the first field, jjones@example.com as the second field and $ 4321.00 as a monthly salary stored in the third field. (The up-arrow (^) above is the standard Pick notation of a field mark; that is, xFE). Thus the first three fields of this record, including the record ID and trailing field mark, would use 49 bytes of storage. A given value uses only as many bytes as needed. For example, in another record of

322-412: A result row. The result of the join can be defined as the outcome of first taking the cartesian product (or cross join ) of all rows in the tables (combining every row in table A with every row in table B) and then returning all rows that satisfy the join predicate. Actual SQL implementations normally use other approaches, such as hash joins or sort-merge joins , since computing the Cartesian product

368-481: A set of Client Tools to allow software developers to access U2 databases from other software languages. Client Tool interfaces include: Both UniVerse and UniData support TLS transport level data encryption and record and file level encryption of data at rest using OpenSSL. Additional API encryption functionality is also available to allow custom solutions or meet specific regulatory requirements. RocketU2 offers three professional certification designations related to

414-447: A theoretical concept for discussion. The above sample query for inner joins can be expressed as a natural join in the following way: As with the explicit USING clause, only one DepartmentID column occurs in the joined table, with no qualifier: PostgreSQL, MySQL and Oracle support natural joins; Microsoft T-SQL and IBM DB2 do not. The columns used in the join are implicit so the join code does not show which columns are expected, and

460-530: Is point-of-sale software. Join (SQL)#Outer join A join clause in the Structured Query Language ( SQL ) combines columns from one or more tables into a new table. The operation corresponds to a join operation in relational algebra . Informally, a join stitches two tables and puts on the same row records with matching fields : INNER , LEFT OUTER , RIGHT OUTER , FULL OUTER and CROSS . To explain join types,

506-490: Is a commonly used join operation in applications but should not be assumed to be the best choice in all situations. Inner join creates a new result table by combining column values of two tables (A and B) based upon the join-predicate. The query compares each row of A with each row of B to find all pairs of rows that satisfy the join-predicate. When the join-predicate is satisfied by matching non- NULL values, column values for each matched pair of rows of A and B are combined into

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552-435: Is a specific type of comparator-based join, that uses only equality comparisons in the join-predicate. Using other comparison operators (such as < ) disqualifies a join as an equi-join. The query shown above has already provided an example of an equi-join: We can write equi-join as below, If columns in an equi-join have the same name, SQL-92 provides an optional shorthand notation for expressing equi-joins, by way of

598-507: Is aimed at addressing the needs of any given business within a discernible vertical market (specific industry or market). While horizontal market software can be useful to a wide array of industries (such as word processors or spreadsheet programs), vertical market software is developed for and customized to a specific industry's needs. Vertical market software is readily identifiable by the application specific graphical user interface which defines it. One example of vertical market software

644-451: Is not an option in large databases with hundreds or thousands of tables where it would place an unrealistic constraint on naming conventions. Real world databases are commonly designed with foreign key data that is not consistently populated (NULL values are allowed), due to business rules and context. It is common practice to modify column names of similar data in different tables and this lack of rigid consistency relegates natural joins to

690-497: Is not supported by MS SQL Server and Sybase. The natural join is a special case of equi-join. Natural join (⋈) is a binary operator that is written as ( R ⋈ S ) where R and S are relations . The result of the natural join is the set of all combinations of tuples in R and S that are equal on their common attribute names. For an example consider the tables Employee and Dept and their natural join: This can also be used to define composition of relations . For example,

736-454: Is slower and would often require a prohibitively large amount of memory to store. SQL specifies two different syntactical ways to express joins: the "explicit join notation" and the "implicit join notation". The "implicit join notation" is no longer considered a best practice , although database systems still support it. The "explicit join notation" uses the JOIN keyword, optionally preceded by

782-466: Is stored as a subdirectory within the account directory on the host operating system and may be read or edited using appropriate tools. Files are made of records, which are similar to rows within tables of a relational database. Each record has a unique key (called a "record ID") to distinguish it from other records in the file. These record IDs are typically hashed so that data can be retrieved quickly and efficiently. Records (including record IDs) store

828-664: The INNER keyword, to specify the table to join, and the ON keyword to specify the predicates for the join, as in the following example: The "implicit join notation" simply lists the tables for joining, in the FROM clause of the SELECT statement, using commas to separate them. Thus it specifies a cross join , and the WHERE clause may apply additional filter-predicates (which function comparably to

874-545: The USING construct: The USING construct is more than mere syntactic sugar , however, since the result set differs from the result set of the version with the explicit predicate. Specifically, any columns mentioned in the USING list will appear only once, with an unqualified name, rather than once for each table in the join. In the case above, there will be a single DepartmentID column and no employee.DepartmentID or department.DepartmentID . The USING clause

920-460: The Cartesian product of rows from tables in the join. In other words, it will produce rows which combine each row from the first table with each row from the second table. Example of an explicit cross join: Example of an implicit cross join: The cross join can be replaced with an inner join with an always-true condition: CROSS JOIN does not itself apply any predicate to filter rows from

966-456: The join predicate arises implicitly by comparing all columns in both tables that have the same column-names in the joined tables. The resulting joined table contains only one column for each pair of equally named columns. In the case that no columns with the same names are found, the result is a cross join . Most experts agree that NATURAL JOINs are dangerous and therefore strongly discourage their use. The danger comes from inadvertently adding

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1012-517: The U2 product family. Rocket Software Universe and Unidata have limited ability to create web-based front-ends to Universe/UniData content. Since Rocket Software provides SQL access to its database products, a SQL-based product can be used to build a web-based UI to the databases; regardless of using Files or Tables in U2. A third-party application framework, can be used to build such web interfaces. Vertical market software Vertical market software

1058-463: The actual data as pure ASCII strings; there is no binary data stored in U2. For example, the hardware representation of a floating-point number would be converted to its ASCII equivalent before being stored. Usually these records are divided into fields (which are sometimes called "attributes" in U2). Each field is separated by a "field mark" (hexadecimal character FE). Thus this string: might represent

1104-403: The attribute names unique to R and let s 1 , ..., s k be the attributes unique to S . Furthermore, assume that the attribute names x 1 , ..., x m are neither in R nor in S . In a first step the common attribute names in S can now be renamed: Then we take the Cartesian product and select the tuples that are to be joined: A natural join is a type of equi-join where

1150-436: The composition of Employee and Dept is their join as shown above, projected on all but the common attribute DeptName . In category theory , the join is precisely the fiber product . The natural join is arguably one of the most important operators since it is the relational counterpart of logical AND. Note that if the same variable appears in each of two predicates that are connected by AND, then that variable stands for

1196-529: The contents or to output the contents of a file. For hashed files, a U2 system uses a hashing algorithm to allocate the file's records into groups based on the record IDs . When searching for data in a hashed file, the system only searches the group where the record ID is stored, making the search process more efficient and quicker than searching through the whole file. Nonhashed files are used to store data with little or no logical structure such as program source code , XML or plain text . This type of file

1242-515: The database design and data characteristics. A left outer join can usually be substituted for an inner join when the join columns in one table may contain NULL values. Any data column that may be NULL (empty) should never be used as a link in an inner join, unless the intended result is to eliminate the rows with the NULL value. If NULL join columns are to be deliberately removed from the result set , an inner join can be faster than an outer join because

1288-609: The database division of Informix in April 2001, making UniVerse and UniData part of IBM's DB2 product family. IBM subsequently created the Information Management group of which Data Management is one of the sub-areas under which the IBM U2 family comprised UniData and UniVerse along with the tools, SystemBuilder Extensible Architecture (SB/XA), U2 Web Development Environment (U2 Web DE) and wIntegrate. On 1 October 2009 it

1334-484: The department ID 35 ("Marketing"). Depending on the desired results, this behavior may be a subtle bug, which can be avoided by replacing the inner join with an outer join . Programmers should take special care when joining tables on columns that can contain NULL values, since NULL will never match any other value (not even NULL itself), unless the join condition explicitly uses a combination predicate that first checks that

1380-409: The foreign key holds between attributes with the same name. If this is not the case such as in the foreign key from Dept . manager to Employee . Name then these columns have to be renamed before the natural join is taken. Such a join is sometimes also referred to as an equi-join . More formally the semantics of the natural join are defined as follows: where Fun is a predicate that is true for

1426-495: The form of fields/attributes like his name, address etc. Both UniVerse and UniData have a structured BASIC language (UniVerse Basic and UniBasic, respectively), similar to Pick/BASIC which naturally operates on the structures of the MultiValue database. They also have a structured database query language (RetrieVe and UniQuery) used to select records for further processing and for ad hoc queries and reports. RocketU2 provides

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1472-486: The join-condition does not find any matching row in the "right" table (B). This means that if the ON clause matches 0 (zero) rows in B (for a given row in A), the join will still return a row in the result (for that row)—but with NULL in each column from B. A left outer join returns all the values from an inner join plus all values in the left table that do not match to the right table, including rows with NULL (empty) values in

1518-627: The join-predicates in the explicit notation). The following example is equivalent to the previous one, but this time using implicit join notation: The queries given in the examples above will join the Employee and department tables using the DepartmentID column of both tables. Where the DepartmentID of these tables match (i.e. the join-predicate is satisfied), the query will combine the LastName , DepartmentID and DepartmentName columns from

1564-423: The joined table. The results of a CROSS JOIN can be filtered using a WHERE clause, which may then produce the equivalent of an inner join. In the SQL:2011 standard, cross joins are part of the optional F401, "Extended joined table", package. Normal uses are for checking the server's performance. An inner join (or join ) requires each row in the two joined tables to have matching column values, and

1610-931: The joins columns are NOT NULL before applying the remaining predicate condition(s). The Inner Join can only be safely used in a database that enforces referential integrity or where the join columns are guaranteed not to be NULL. Many transaction processing relational databases rely on atomicity, consistency, isolation, durability (ACID) data update standards to ensure data integrity, making inner joins an appropriate choice. However, transaction databases usually also have desirable join columns that are allowed to be NULL. Many reporting relational database and data warehouses use high volume extract, transform, load (ETL) batch updates which make referential integrity difficult or impossible to enforce, resulting in potentially NULL join columns that an SQL query author cannot modify and which cause inner joins to omit data with no indication of an error. The choice to use an inner join depends on

1656-462: The link column. For example, this allows us to find an employee's department, but still shows employees that have not been assigned to a department (contrary to the inner-join example above, where unassigned employees were excluded from the result). Example of a left outer join (the OUTER keyword is optional), with the additional result row (compared with the inner join) italicized: Oracle supports

1702-405: The number of rows using the filter that depends on a calculated value, resulting in a relatively enormous amount of inefficient processing. When a result set is produced by joining several tables, including master tables used to look up full-text descriptions of numeric identifier codes (a Lookup table ), a NULL value in any one of the foreign keys can result in the entire row being eliminated from

1748-519: The record may be updated to: where the close bracket (]) represents a value mark. Since each email address can be the ID of a record in separate file (in SQL terms, an outer join ; in U2 terms, a "translate"), this provides the reason why U2 may be classified as a MultiValued database. Raw information is called Data. A record is a set of logical grouped data . e.g. an employee record will have data stored in

1794-530: The rest of this article uses the following tables: Department.DepartmentID is the primary key of the Department table, whereas Employee.DepartmentID is a foreign key . Note that in Employee , "Williams" has not yet been assigned to a department. Also, no employees have been assigned to the "Marketing" department. These are the SQL statements to create the above tables: CROSS JOIN returns

1840-593: The result set, with no indication of error. A complex SQL query that includes one or more inner joins and several outer joins has the same risk for NULL values in the inner join link columns. A commitment to SQL code containing inner joins assumes NULL join columns will not be introduced by future changes, including vendor updates, design changes and bulk processing outside of the application's data validation rules such as data conversions, migrations, bulk imports and merges. One can further classify inner joins as equi-joins, as natural joins, or as cross-joins. An equi-join

1886-403: The same file, JOHN JONES (10 bytes) may be replaced by MARJORIE Q. HUMPERDINK (21 bytes) yet each name uses only as much storage as it needs, plus one for the field mark. Fields may be broken down into values and even subvalues. Values are separated by value marks (character xFD); subvalues are separated by subvalue marks (character xFC). Thus, if John Jones happened to get a second email address,

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1932-418: The same thing and both appearances must always be substituted by the same value. In particular, the natural join allows the combination of relations that are associated by a foreign key . For example, in the above example a foreign key probably holds from Employee . DeptName to Dept . DeptName and then the natural join of Employee and Dept combines all employees with their departments. This works because

1978-442: The table join and filtering is done in a single step. Conversely, an inner join can result in disastrously slow performance or even a server crash when used in a large volume query in combination with database functions in an SQL Where clause. A function in an SQL Where clause can result in the database ignoring relatively compact table indexes. The database may read and inner join the selected columns from both tables before reducing

2024-409: The two sides of the JOIN keyword). Like inner joins , one can further sub-categorize all types of outer joins as equi-joins , natural joins , ON <predicate> ( θ -join ), etc. No implicit join-notation for outer joins exists in standard SQL. The result of a left outer join (or simply left join ) for tables A and B always contains all rows of the "left" table (A), even if

2070-399: The two tables into a result row. Where the DepartmentID does not match, no result row is generated. Thus the result of the execution of the query above will be: The employee "Williams" and the department "Marketing" do not appear in the query execution results. Neither of these has any matching rows in the other respective table: "Williams" has no associated department, and no employee has

2116-535: Was announced that Rocket Software had purchased the entire U2 portfolio from IBM. The U2 portfolio is grouped under the name RocketU2. Systems are made of one or more accounts. Accounts are directories stored on the host operating system that initially contain the set of files needed for the system to function properly. This includes the system's VOC ( vocabulary ) file that contains every command , filename , keyword , alias , script , and other pointers . Each of these classes of VOC entries can also be created by

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