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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. 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 purpose of DQL commands is to get the schema relation based on the query passed to it. Although often considered part of DML, the SQL SELECT statement is strictly speaking an example of DQL. When adding FROM or WHERE data manipulators to the SELECT statement the statement is then considered part of the DML.
In the most SQL dialects the double dash (--) can be used instead. Esoteric languages. Many esoteric programming languages follow the convention that any text not executed by the instruction pointer (e.g., Befunge) or otherwise assigned a meaning (e.g., Brainfuck), is considered a "comment".
Similar commands are available in many SQL systems, but usually as external tools, as opposed to being internal to the SQL language. This makes them unavailable to stored procedures. QUEL has an extremely powerful aggregation capability. Aggregates can be nested, and different aggregates can have independent by-lists and/or restriction clauses.
A query language, also known as data query language or database query language (DQL), is a computer language used to make queries in databases and information systems. In database systems, query languages rely on strict theory to retrieve information. [1] A well known example is the Structured Query Language (SQL).
Note (1): Both function and procedure refer to internal routines written in SQL and/or procedural language like PL/SQL. External routine refers to the one written in the host languages, such as C, Java, Cobol, etc. "Stored procedure" is a commonly used term for these routine types. However, its definition varies between different database vendors.
ISO/IEC 9075 "Information technology - Database languages - SQL" is an international standard for Structured Query Language, and is considered as specifying the minimum for what a database engine should fulfill in terms of SQL syntax, which is called Core SQL. The standard also defines a number of optional features.
In SQL, the data manipulation language comprises the SQL-data change statements, [3] which modify stored data but not the schema or database objects. Manipulation of persistent database objects, e.g., tables or stored procedures, via the SQL schema statements, [3] rather than the data stored within them, is considered to be part of a separate data definition language (DDL).