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SQL includes operators and functions for calculating values on stored values. SQL allows the use of expressions in the select list to project data, as in the following example, which returns a list of books that cost more than 100.00 with an additional sales_tax column containing a sales tax figure calculated at 6% of the price.
The CASE expression, for example, enables SQL to perform conditional branching within queries, providing a mechanism to return different values based on evaluated conditions. This logic can be particularly useful for data transformation during retrieval, especially in SELECT statements.
In the searched CASE expression, the string 'Null Result' is returned for all rows in which i is Null. Oracle's dialect of SQL provides a built-in function DECODE which can be used instead of the simple CASE expressions and considers two nulls equal.
The SQL CASE expression is a generalization of the ternary operator. Instead of one conditional and two results, n conditionals and n+1 results can be specified. With one conditional it is equivalent (although more verbose) to the ternary operator:
The WHERE clause is not the only clause where sargability can matter; it can also have an effect on ORDER BY, GROUP BY and HAVING clauses. The SELECT clause, on the other hand, can contain non-sargable expressions without adversely affecting the performance. Some database management systems, for instance PostgreSQL, support functional indices ...
In Oracle SQL, most operations and searches are case-sensitive by default, [6] while in most other DBMSes, SQL searches are case-insensitive by default. [7] Case-insensitive operations are sometimes said to fold case, from the idea of folding the character code table so that upper- and lowercase letters coincide.
SQL-92 was the third revision of the SQL database query language. Unlike SQL-89, it was a major revision of the standard. Aside from a few minor incompatibilities, the SQL-89 standard is forward-compatible with SQL-92. The standard specification itself grew about five times compared to SQL-89.
SQL:2008 is the sixth revision of the ISO and ANSI standard for the SQL database query language. It was formally adopted in July 2008. [ 1 ] The standard consists of 9 parts which are described in detail in SQL .