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In very early versions of the SQL standard the return code was called SQLCODE and used a different coding schema. The following table lists the standard-conforming values - based on SQL:2011. [1] The table's last column shows the part of the standard that defines the row. If it is empty, the definition originates from part 2 Foundation.
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 ...
The concept of Null is the subject of some debate. The Null marker indicates the absence of a value, and is distinct from a value of 0 for an integer column or an empty string for a text column. The concept of Nulls enforces the 3-valued-logic in SQL, which is a concrete implementation of the general 3-valued logic. [12]
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 the table join and filtering is done in a single step ...
The BIT data type, which can only store integers 0 and 1 apart from NULL, is commonly used as a workaround to store Boolean values, but workarounds need to be used such as UPDATE t SET flag = IIF (col IS NOT NULL, 1, 0) WHERE flag = 0 to convert between the integer and Boolean expression.
By returning a null object (i.e., an empty list) instead, there is no need to verify that the return value is in fact a list. The calling function may simply iterate the list as normal, effectively doing nothing. It is, however, still possible to check whether the return value is a null object (an empty list) and react differently if desired.
Reserved words in SQL and related products In SQL:2023 [3] In IBM Db2 13 [4] In Mimer SQL 11.0 [5] In MySQL 8.0 [6] In Oracle Database 23c [7] In PostgreSQL 16 [1] In Microsoft SQL Server 2022 [2]
The null coalescing operator is a binary operator that is part of the syntax for a basic conditional expression in several programming languages, such as (in alphabetical order): C# [1] since version 2.0, [2] Dart [3] since version 1.12.0, [4] PHP since version 7.0.0, [5] Perl since version 5.10 as logical defined-or, [6] PowerShell since 7.0.0, [7] and Swift [8] as nil-coalescing operator.