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A lookup table, which contains, as keys, the case values and, as values, the part under the case statement. (In some languages, only actual data types are allowed as values in the lookup table. In other languages, it is also possible to assign functions as lookup table values, gaining the same flexibility as a real switch statement.
The DUAL table is a special one-row, one-column table present by default in Oracle and other database installations. In Oracle, the table has a single VARCHAR2(1) column called DUMMY that has a value of 'X'. It is suitable for use in selecting a pseudo column such as SYSDATE or USER.
This syntax uses implicit equality comparisons, with the usual caveats for comparing with NULL. There are two short forms for special CASE expressions: COALESCE and NULLIF. The COALESCE expression returns the value of the first non-NULL operand, found by working from left to right, or NULL if all the operands equal NULL.
E. F. Codd mentioned nulls as a method of representing missing data in the relational model in a 1975 paper in the FDT Bulletin of ACM-SIGMOD.Codd's paper that is most commonly cited with the semantics of Null (as adopted in SQL) is his 1979 paper in the ACM Transactions on Database Systems, in which he also introduced his Relational Model/Tasmania, although much of the other proposals from ...
Syntax is usually associated with the rules (or grammar) governing the composition of texts in a formal language that constitute the well-formed formulas of a formal system. In computer science, the term syntax refers to the rules governing the composition of well-formed expressions in a programming language. As in mathematical logic, it is ...
an oracle tape, which is a semi-infinite tape separate from the work tape. The alphabet for the oracle tape may be different from the alphabet for the work tape. an oracle head which, like the read/write head, can move left or right along the oracle tape reading and writing symbols; two special states: the ASK state and the RESPONSE state.
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] The name recalls signal processing window functions. A window function call always contains an OVER clause.
A pseudo-oracle, as defined by Weyuker, [12] is a separately written program which can take the same input as the program or SUT so that their outputs may be compared to understand if there might be a problem to investigate. A partial oracle [6]: 515 is a hybrid between specified test oracle and derived test oracle. It specifies important (but ...