All variables, rows and records used in a block must be declared in the declarations section of the block. (The only exception is that the loop variable of a FOR loop iterating over a range of integer values is automatically declared as an integer variable.)
PL/pgSQL variables can have any SQL data type, such as INTEGER, VARCHAR and CHAR.
Here are some examples of variable declarations:
user_id INTEGER; quantity NUMERIC(5); url VARCHAR;
The general syntax of a variable declaration is:
name [ CONSTANT ] type [ NOT NULL ] [ { DEFAULT | := } expression ];
The DEFAULT clause, if given, specifies the initial value assigned to the variable when the block is entered. If the DEFAULT clause is not given then the variable is initialized to the SQL NULL value.
The CONSTANT option prevents the variable from being assigned to, so that its value remains constant for the duration of the block. If NOT NULL is specified, an assignment of a NULL value results in a runtime error. All variables declared as NOT NULL must have a non-NULL default value specified.
The default value is evaluated every time the block is entered. So, for example, assigning 'now' to a variable of type timestamp causes the variable to have the time of the current function call, not when the function was precompiled.
Examples:
quantity INTEGER DEFAULT 32; url varchar := ''http://mysite.com''; user_id CONSTANT INTEGER := 10;
name ALIAS FOR $n;
Parameters passed to functions are named with the identifiers $1, $2, etc. Optionally, aliases can be declared for $n parameter names for increased readability. Either the alias or the numeric identifier can then be used to refer to the parameter value. Some examples:
CREATE FUNCTION sales_tax(REAL) RETURNS REAL AS '
DECLARE
subtotal ALIAS FOR $1;
BEGIN
return subtotal * 0.06;
END;
' LANGUAGE 'plpgsql';
CREATE FUNCTION instr(VARCHAR,INTEGER) RETURNS INTEGER AS '
DECLARE
v_string ALIAS FOR $1;
index ALIAS FOR $2;
BEGIN
-- Some computations here
END;
' LANGUAGE 'plpgsql';
name tablename%ROWTYPE;
A variable of a composite type is called a row variable (or rowtype variable). Such a variable can hold a whole row of a SELECT or FOR query result, so long as that query's column set matches the declared type of the variable. The individual fields of the row value are accessed using the usual dot notation, for example rowvar.field.
Presently, a row variable can only be declared using the %ROWTYPE notation; although one might expect a bare table name to work as a type declaration, it won't be accepted within PL/pgSQL functions.
Parameters to a function can be composite types (complete table rows). In that case, the corresponding identifier $n will be a row variable, and fields can be selected from it, for example $1.user_id.
Only the user-defined attributes of a table row are accessible in a rowtype variable, not OID or other system attributes (because the row could be from a view). The fields of the rowtype inherit the table's field size or precision for data types such as char(n).
name RECORD;
Record variables are similar to rowtype variables, but they have no predefined structure. They take on the actual row structure of the row they are assigned during a SELECT or FOR command. The substructure of a record variable can change each time it is assigned to. A consequence of this is that until a record variable is first assigned to, it has no substructure, and any attempt to access a field in it will draw a runtime error.
Note that RECORD is not a true datatype, only a placeholder. Thus, for example, one cannot declare a function returning RECORD.
Using the %TYPE and %ROWTYPE attributes, you can declare variables with the same data type or structure as another database item (e.g: a table field).
%TYPE provides the data type of a variable or database column. You can use this to declare variables that will hold database values. For example, let's say you have a column named user_id in your users table. To declare a variable with the same data type as users.user_id you write:
user_id users.user_id%TYPE;
By using %TYPE you don't need to know the data type of the structure you are referencing, and most important, if the data type of the referenced item changes in the future (e.g: you change your table definition of user_id from INTEGER to REAL), you may not need to change your function definition.
%ROWTYPE provides the composite data type corresponding to a whole row of the specified table. table must be an existing table or view name of the database.
DECLARE
users_rec users%ROWTYPE;
user_id users.user_id%TYPE;
BEGIN
user_id := users_rec.user_id;
...
CREATE FUNCTION does_view_exist(INTEGER) RETURNS bool AS '
DECLARE
key ALIAS FOR $1;
table_data cs_materialized_views%ROWTYPE;
BEGIN
SELECT INTO table_data * FROM cs_materialized_views
WHERE sort_key=key;
IF NOT FOUND THEN
RETURN false;
END IF;
RETURN true;
END;
' LANGUAGE 'plpgsql';
RENAME oldname TO newname;
Using the RENAME declaration you can change the name of a variable, record or row. This is primarily useful if NEW or OLD should be referenced by another name inside a trigger procedure. See also ALIAS.
Examples:
RENAME id TO user_id; RENAME this_var TO that_var;
Note: RENAME appears to be broken as of PostgreSQL 7.2. Fixing this is of low priority, since ALIAS covers most of the practical uses of RENAME.