![]() LEAST() and GREATEST()are examples of such functions.īy default, string comparisons are not case-sensitve and use the current character set. Some of the functions in this section return values other than 1(TRUE), 0(FALSE), or NULL. String are automatically converted to numbers and numbers to string as necessary. These operations work for both numbers and strings. Whether a value is niot within a set of valuesĬomparison operations retult in a value of 1(TRUE), 0(FALSE), or NULL. Whether a value is not within a range of values Return the index of the argument that is less than the first argument Whether a value is within a set of values SQL Server’s deprecated ANSI_NULLS setting makes some equals comparison ( =) act as though it was a is not distinct from comparison.Whether a value is within a range of values MySQL offers the proprietary comparison operator that works like is not distinct from. The is operator of SQLite ( documentation) and H2 ( documentation) is able to compare two expressions (not just is null), and it has the same semantics as is not distinct from. 2 The following example has the same effect as A is not distinct from B: DECODE(A, B, 0, 1) = 0 is - SQLite, H2 The standard solution using exists, values, and intersect can easily be modified to work on more databases by using select without from instead of the values clause: EXISTS (SELECT c1ĭb2, Oracle database, and H2 have the proprietary function decode that happens to use is not distinct from semantics internally. 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. Available in 11.1 Mod Pack 1/Fix Pack 1.BigQuery Db2 (LUW) a a MariaDB MySQL Oracle DB PostgreSQL SQL Server SQLite is distinct from is not distinct from Using case and is null Using intersect, values, exists 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. Īnother option is to use table operators, which use distinct comparisons internally. I make my living from SQL training, SQL tuning and consulting and my book “SQL Performance Explained”. 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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