Sql does not equal12/20/2023 BigQuery Db2 (LUW) MariaDB MySQL Oracle DB PostgreSQL SQL Server SQLite intersect, select w/o from decode(A, B, 0, 1) = 0 A is B A B Exists, select without from, intersect they have a two-valued result and never return unknown. The following proprietary features are fully compatible-i.e. Most database that do not offer is not distinct from offer a proprietary alternative that is more convenient than the conforming alternative described above. BigQuery Db2 (LUW) MariaDB MySQL Oracle DB PostgreSQL SQL Server SQLite is distinct from is not distinct from Using case and is null Using intersect, values, exists Proprietary Alternatives The optional negation with not was added by SQL:2003 as feature T152, “DISTINCT predicate with negation”. The is distinct from predicate was introduced in two steps: SQL:1999 added T151, “DISTINCT predicate”. A select from a one-row dummy table can be used to get a conforming and widely supported solution. Unfortunately, it doesn’t work on all databases due to the use of the values clause. This has the advantage that it does not repeat any expressions. This logic can be easily tested in the where clause with an exists predicate: 1 EXISTS (VALUES (A) If it is twice the same value the common subset will be that value. The two compared sets are just one value each (one row with one column). The following snippet uses intersect to determine a common subset. Buying my book “SQL Performance Explained” (from €9.95) also supports my work on this website.Īnother option is to use table operators, which use distinct comparisons internally. I offer SQL training, tuning and consulting. This technique is explained in “ Binary Decisions Based on Three-Valued Results”. In some databases is not false can be used instead of the case expression. either true or false but never unknown-the case expression reduces the three-valued result into a two-valued one. To get the fully equivalent functionality of is not distinct from-i.e. This is often not a problem because SQL generally treats unknown like false when making binary decisions such as accepting or rejecting a row for a where clause. If only one argument is null the result is unknown, not false. The result of the expression in the when clause is true if both arguments are equal or both are null. 0 CASE WHEN (a = b) or (a IS NULL AND b IS NULL) Although there are standard alternatives to is not distinct from, using a proprietary alternative is often the better choice.ĭue to SQL’s three-valued logic, a fully equivalent substitute for A is not distinct from B that works in all SQL databases is surprisingly complex-even when we limit the requirement to cases where evaluating the expressions A and B is deterministic and has no side-effects.
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