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  2. Aggregate function - Wikipedia

    en.wikipedia.org/wiki/Aggregate_function

    The input and output domains may be the same, such as for SUM, or may be different, such as for COUNT. Aggregate functions occur commonly in numerous programming languages, in spreadsheets, and in relational algebra. The listagg function, as defined in the SQL:2016 standard [2] aggregates data from multiple rows into a single concatenated string.

  3. Having (SQL) - Wikipedia

    en.wikipedia.org/wiki/Having_(SQL)

    WHERE is taken into account at an earlier stage of a query execution, filtering the rows read from the tables. If a query contains GROUP BY, rows from the tables are grouped and aggregated. After the aggregating operation, HAVING is applied, filtering out the rows that don't match the specified conditions. Therefore, WHERE applies to data read ...

  4. Select (SQL) - Wikipedia

    en.wikipedia.org/wiki/Select_(SQL)

    The SQL SELECT statement returns a result set of rows, from one or more tables. [ 1 ][ 2 ] A SELECT statement retrieves zero or more rows from one or more database tables or database views. In most applications, SELECT is the most commonly used data manipulation language (DML) command. As SQL is a declarative programming language, SELECT ...

  5. Group by (SQL) - Wikipedia

    en.wikipedia.org/wiki/Group_by_(SQL)

    Group by (SQL) A GROUP BY statement in SQL specifies that a SQL SELECT statement partitions result rows into groups, based on their values in one or several columns. Typically, grouping is used to apply some sort of aggregate function for each group. [1][2] The result of a query using a GROUP BY statement contains one row for each group.

  6. Set operations (SQL) - Wikipedia

    en.wikipedia.org/wiki/Set_operations_(SQL)

    Set operations (SQL) Set operations in SQL is a type of operations which allow the results of multiple queries to be combined into a single result set. [ 1] Set operators in SQL include UNION, INTERSECT, and EXCEPT, which mathematically correspond to the concepts of union, intersection and set difference .

  7. List of hash functions - Wikipedia

    en.wikipedia.org/wiki/List_of_hash_functions

    sum with circular rotation SYSV checksum (Unix) 16 bits sum with circular rotation sum8 8 bits sum Internet Checksum: 16 bits sum (ones' complement) sum24 24 bits sum sum32 32 bits sum fletcher-4: 4 bits sum fletcher-8: 8 bits sum fletcher-16: 16 bits sum fletcher-32: 32 bits sum Adler-32: 32 bits sum xor8: 8 bits sum Luhn algorithm: 1 decimal ...

  8. Entity–relationship model - Wikipedia

    en.wikipedia.org/wiki/Entity–relationship_model

    Entity–relationship model. An entity–attribute-relationship diagram for an MMORPG using Chen's notation. An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships ...

  9. Hierarchical and recursive queries in SQL - Wikipedia

    en.wikipedia.org/wiki/Hierarchical_and_recursive...

    In SQL:1999 a recursive (CTE) query may appear anywhere a query is allowed. It's possible, for example, to name the result using CREATE [ RECURSIVE ] VIEW . [ 15 ] Using a CTE inside an INSERT INTO , one can populate a table with data generated from a recursive query; random data generation is possible using this technique without using any ...