SQL syntax

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The syntax of the SQL programming language is defined and maintained by ISO/IEC SC 32 as part of ISO/IEC 9075. This standard is not freely available. Despite the existence of the standard, SQL code is not completely portable among different database systems without adjustments. The SQL language is subdivided into several language elements, including: Other operators have at times been suggested or implemented, such as the skyline operator (for finding only those rows that are not 'worse' than any others). SQL has the case expression, which was introduced in SQL-92. In its most general form, which is called a "searched case" in the SQL standard: SQL tests WHEN conditions in the order they appear in the source. If the source does not specify an ELSE expression, SQL defaults to ELSE NULL. An abbreviated syntax called "simple case" can also be used: 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. is equivalent to: The NULLIF expression has two operands and returns NULL if the operands have the same value, otherwise it has the value of the first operand. is equivalent to Standard SQL allows two formats for comments: -- comment, which is ended by the first newline, and /* comment */, which can span multiple lines.