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  2. SQL syntax - Wikipedia

    en.wikipedia.org/wiki/SQL_syntax

    Each column in an SQL table declares the type(s) that column may contain. ANSI SQL includes the following data types. [14] Character strings and national character strings. CHARACTER(n) (or CHAR(n)): fixed-width n-character string, padded with spaces as needed; CHARACTER VARYING(n) (or VARCHAR(n)): variable-width string with a maximum size of n ...

  3. Select (SQL) - Wikipedia

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

    by adding a SQL window function to the SELECT-statement; ISO SQL:2008 introduced the FETCH FIRST clause. According to PostgreSQL v.9 documentation, an SQL window function "performs a calculation across a set of table rows that are somehow related to the current row", in a way similar to aggregate functions. [7]

  4. Set operations (SQL) - Wikipedia

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

    The SQL EXCEPT operator takes the distinct rows of one query and returns the rows that do not appear in a second result set. For purposes of row elimination and duplicate removal, the EXCEPT operator does not distinguish between NULLs .

  5. Unique key - Wikipedia

    en.wikipedia.org/wiki/Unique_key

    In SQL, the unique keys have a UNIQUE constraint assigned to them in order to prevent duplicates (a duplicate entry is not valid in a unique column). Alternate keys may be used like the primary key when doing a single-table select or when filtering in a where clause, but are not typically used to join multiple tables.

  6. Cursor (databases) - Wikipedia

    en.wikipedia.org/wiki/Cursor_(databases)

    Before code can access the data, it must open the cursor with the OPEN statement. Directly following a successful opening, the cursor is positioned before the first row in the result set. OPEN cursor_name. Applications position cursors on a specific row in the result set with the FETCH statement. A fetch operation transfers the data of the row ...

  7. Insert (SQL) - Wikipedia

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

    Most systems do not allow SQL INSERT statements to return row data. Therefore, it becomes necessary to implement a workaround in such scenarios. Common implementations include: Using a database-specific stored procedure that generates the surrogate key, performs the INSERT operation, and finally returns

  8. Entity–attribute–value model - Wikipedia

    en.wikipedia.org/wiki/Entity–attribute–value...

    Row modeling, [clarification needed] where facts about something (in this case, a sales transaction) are recorded as multiple rows rather than multiple columns, is a standard data modeling technique. The differences between row modeling and EAV (which may be considered a generalization of row-modeling) are:

  9. Check constraint - Wikipedia

    en.wikipedia.org/wiki/Check_constraint

    It can refer to a single column, or multiple columns of the table. The result of the predicate can be either TRUE , FALSE , or UNKNOWN , depending on the presence of NULLs . If the predicate evaluates to UNKNOWN , then the constraint is not violated and the row can be inserted or updated in the table.