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Database querying using SQL
Published in Benjamin S. Baumer, Daniel T. Kaplan, Nicholas J. Horton, Modern Data Science with R, 2021
Benjamin S. Baumer, Daniel T. Kaplan, Nicholas J. Horton
Recall that in a JOIN—also known as an inner or natural or regularJOIN—all possible matching pairs of rows from the two tables are included. Thus, if the first table has n rows and the second table has m, as many as nm rows could be returned. However, in the airports table each row has a unique airport code, and thus every row in flights will match the destination field to at most one row in the airports table. What happens if no such entry is present in airports? That is, what happens if there is a destination airport in flights that has no corresponding entry in airports? If you are using a JOIN, then the offending row in flights is simply not returned. On the other hand, if you are using a LEFT JOIN, then every row in the first table is returned, and the corresponding entries from the second table are left blank. In this example, no airport names were found for several airports.
Geologic database management
Published in Martin Lloyd Smith, Geologic and Mine Modelling using Techbase and Lynx, 2020
Polygon tables are used to store two- or three-dimensional polygons. One common use of polygons is to define lease or claim boundaries, but they are also very useful during production scheduling. Mining cuts are defined as polygons and are intersected with cell, block or layer tables in production volumetric calculations. This method is used to determine the average ore grade and tonnage of lifts and bench cuts. The polygon table can be used to keep track of production history. While all of the above tables can be found in comprehensive geologic and mining software, Techbase includes an additional table type which is peculiar to its database structure: the join table. Join tables are used to connect one table with another so that fields contained in both tables can be used simultaneously. Usually, there is a many-to-few relationship between records in the two tables which are to be joined (see Fig. 2.2). A join table is commonly used with the flat tables containing drillhole data. Drillhole log data is not commonly provided with the xyz coordinates of samples or lithologic boundaries; instead, it is necessary to calculate the xyz coordinates using the collar location, the from/to depth intervals down the hole and survey information on the inclination of the hole. Since the three flat tables which hold this information have different numbers of records, there must be a means of connecting them. This connectivity is accomplished through the join table, and will be discussed in depth under Compositing (see Section 4.1).
J
Published in Phillip A. Laplante, Dictionary of Computer Science, Engineering, and Technology, 2017
(2) in languages operating on databases, an operator used to combine related tuples from two relations into single operations. Only operations that satisfy the join condition appear in the result of the operation. It is a composite operator comprising a Cartesian product, a select, and a project. In SQL, a JOIN TABLE allows users to specify a table resulting from a join operation in the FROM clause of a query. See also union, intersect.
Enhancing the smart building supervisory system effectiveness
Published in Intelligent Buildings International, 2022
Dario Masucci, Chiara Foglietta, Stefano Panzieri, Stefano Pizzuti
The data collection query selects the data from multiple tables using a fundamental construct of the SQL language, namely the JOIN operation. In this way it is possible to relate different tables and obtain a combined result on the basis of one or more fields that match the tables involved. For each of the last n commands that have not yet been checked, which have the ‘checked’ field equal to zero, we have identification code of the device expires involved, type of command (on or off), identification code of the device from which to take the measurement of the quantity associated with the command, and the measured value of the associated quantity.
Real-time Twitter data analysis using Hadoop ecosystem
Published in Cogent Engineering, 2018
Anisha P. Rodrigues, Niranjan N. Chiplunkar
In order to rate the tokenized words, the tokenized words have to be mapped with the loaded dictionary. We performed left outer join operation on a table that contains id, word and dictionary table if the word matches with the sentiment word in the dictionary, then a rating is given to the matched word or else NULL value is assigned. A hive table is created to store id, word and then rating.(d) Classification of tweets
Optimizing Join in HIVE Star Schema Using Key/Facts Indexing
Published in IETE Technical Review, 2018
Hussien SH. Abdel Azez, Mohamed H. Khafagy, Fatma A. Omara
Joining all facts and demission table records into one table will produce redundant data which consumes high storage by referencing repeated dimension records by an index field. Repetitions for new records will be eliminated, but still there is non-key fields represented as null fields which is mandatory to write data in structured CSV format and can be loaded into HIVE as a table. Finally, we can run SQL Join query and refill null fields on result using index field.