Language elements

An understanding of the basic syntax of SQL and language elements that are common to many SQL statements can be helpful in using SQL with DB2® for z/OS®.

Characters
The basic symbols of keywords and operators in the SQL language are characters that are classified as letters, digits, or special characters.
Tokens
The basic syntactical units of the SQL language are called tokens. A token consists of one or more characters of which none are blanks, control characters, or characters within a string constant or delimited identifier.
Identifiers
An identifier is a token used to form a name. An identifier in an SQL statement is an SQL identifier or a host identifier.
Naming conventions
The rules for forming a name depend on the type of the object designated by the name.
SQL path
The SQL path is an ordered list of schema names. DB2 uses the path to resolve the schema name for certain unqualified object names that appear in any context other than as the main object of an ALTER, CREATE, DROP, COMMENT, GRANT, RENAME, or REVOKE statement.
Resolution of unqualified object names
Most object names are implicitly or explicitly qualified with a schema name. Synonyms are an exception.
Qualification of unqualified object names
Unqualified object names, other than synonyms, are implicitly qualified. The rules for qualifying a name differ depending on the type of object that the name identifies.
Aliases and synonyms
A table or view can be referred to in an SQL statement by its name, by an alias that has been defined for its name, or by a synonym that has been defined for its name. Thus, aliases and synonyms can be thought of as alternative names for tables and views.
Authorization, privileges, permissions, masks, and object ownership
Users (as identified by an authorization ID) can successfully execute SQL statements only if they have the authority to perform the specified operation. For example, to create a table, a user must be authorized to create tables.
Authorization IDs, roles, and authorization names
Processes can successfully execute SQL statements only if they have the necessary authority. A process derives this authority from its authorization IDs. An authorization ID can also designate a user, a group of users, or a role.
Data types
DB2 supports both IBM®-supplied data types (built-in data types) and user-defined data types (distinct types).
Distinct types
A distinct type is a user-defined data type that shares its internal representation with a built-in data type (its source type), but is considered to be a separate and incompatible data type for most operations.
Promotion of data types
Data types can be classified into groups of related data types. Within such groups, an order of precedence exists in which one data type is considered to precede another data type. This precedence enables DB2 to support the promotion of one data type to another data type that appears later in the precedence order.
Casting between data types
There are many occasions when a value with a given data type needs to be cast (changed) to a different data type or to the same data type with a different length, precision, or scale.
Assignment and comparison
The basic operations of SQL are assignment and comparison.
Rules for result data types
Rules that are applied to the operands of an operation determine the data type of the result. Certain rules apply in certain situations and apply depending on the data type of operands.
Constants
A constant (also called a literal) specifies a value. Constants are classified as string constants or numeric constants. Numeric constants are further classified as integer, floating-point, decimal, or decimal floating-point. String constants are classified as character, graphic, or binary.
Special registers
A special register is a storage area that is defined for an application process by DB2 and is used to store information that can be referenced in SQL statements. A reference to a special register is a reference to a value provided by the current server. If the value is a string, its CCSID is a default CCSID of the current server.
Column names
The meaning of a column name depends on its context.
Variables
A variable in an SQL statement specifies a value that can be changed when the SQL statement is executed. There are several types of variables used in SQL statements.
Functions
A function is an operation denoted by a function name followed by zero or more operands that are enclosed in parentheses.
Expressions
An expression specifies a value and can take a number of different forms.
Predicates
A predicate specifies a condition that is true, false, or unknown about a given row or group.
Search conditions
A search condition specifies a condition that is true, false, or unknown about a given row or group. When the condition is true, the row or group qualifies for the results. When the condition is false or unknown, the row or group does not qualify.
Options affecting SQL
Certain DB2 precompiler or coprocessor options (referred to as SQL processing options), DB2 subsystem parameters (set through the installation panels), bind options, options for CREATE PROCEDURE and ALTER PROCEDURE statements for native SQL procedures, and special registers affect how SQL statements can be composed or determine how SQL statements are processed.
Mappings from SQL to XML
DB2 maps SQL to XML data according to industry standards and performs several different mappings.

Parent topic: SQL: The language of DB2