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RECORD
MemSQL Procedural SQL (MPSQL) supports the RECORD
data type, which is an encapsulated group of named fields. Records support an unlimited number of fields, and each field’s data type can be different. Records in MemSQL are conceptually similar to a struct data type in other programming languages, such as C or C++.
Records can be declared in the body of a user-defined function (UDF) or stored procedure (SP), and can be used in assignment statements or accessed in expressions. In addition, records can be specified as an input parameter or return type for UDFs or SPs.
Syntax
The following syntax declares a new record.
variable_name RECORD(field_definition [, ...]) [data_type_modifier]
{ ; | initialization_clause }
field_definition:
field_name data_type [data_type_modifier]
Arguments
variable_name
The name of the record variable.
field_name
The name of the field.
data_type
Any scalar-valued or non-scalar-valued data type, expect for QUERY
types. For a complete list of data types, see the Data Types topic.
data_type_modifier
The optional modifier for the data type, such as NULL
or NOT NULL
. There are two kinds of optional modifiers in a record declaration: the modifier that applies to the record type itself, and the modifier that applies to each field in the record. By default, a record type is NOT NULL
.
initialization_clause
An optional clause that initializes the record.
Remarks
After a record variable has been declared, new fields cannot be added to the record and existing fields cannot be removed from the record. In addition, the data type for a given field cannot be changed to a different type.
When calling a function or procedure, input parameters and return types are always passed by value. This behavior applies to all types, including records.
Record Declaration and Initialization
Record types are declared in a function or procedure as either an input parameter or as a variable in the DECLARE
block. For example:
CREATE FUNCTION my_function(rec1 RECORD(y INT, z INT)) RETURNS INT AS
DECLARE
-- Declares a new uninitialized record
rec2 RECORD(a VARCHAR(255), b INT, c DATE);
-- Declares an initialized record using ROW()
rec3 RECORD(d INT, e VARCHAR(255)) = ROW(1, "Example");
...
You can initialize a record in the DECLARE
block using the ROW()
built-in function, which creates a new record and assigns the value for each field. To initialize a record variable at the time of declaration, use the =
or :=
assignment operators or the DEFAULT
keyword following the variable name and type. For more information, see the ROW() topic.
The following examples demonstrate how to initialize a record:
rec RECORD(a VARCHAR(255), b INT) = ROW("Example", 1);
rec RECORD(a INT, b INT, c INT) DEFAULT ROW(1, 2, 3);
rec RECORD(a VARCHAR(255), b INT) = NULL;
Field Assignment and Access
To assign the value of a record’s fields, use the following notation:
<record-name>.<field-name> = <value>;
For example, consider the following declared record variable:
rec RECORD(a INT, b VARCHAR(255));
To assign the value of the rec
variable’s fields, use two assignment expressions as shown below:
rec.a = 100;
rec.b = "Example";
Fields are accessed using similar syntax, using the notation <record-name>.<field-name>
. Consider the following example:
...
DECLARE
i INT;
s VARCHAR(255);
rec RECORD(a INT, b VARCHAR(255)) = ROW(100, "Example");
BEGIN
i = rec.a;
s = rec.b;
END
...
In the example above, the value of i
becomes 100
, and the value of s
becomes "Example"
.
Record Example
The following example demonstrates how to pass a record as an input parameter to a function:
DELIMITER //
CREATE FUNCTION rec_copy_example(rec1 RECORD(a INT, b INT))
RETURNS VARCHAR(255) AS
DECLARE
rec2 RECORD(a INT, b INT) = rec1;
result VARCHAR(255) = "";
BEGIN
rec2.a = 100;
result = CONCAT("rec1.a = ", rec1.a, "; rec2.a = ", rec2.a);
RETURN result;
END //
DELIMITER ;
memsql> SELECT rec_copy_example(ROW(1,2));
+----------------------------+
| rec_copy_example(ROW(1,2)) |
+----------------------------+
| rec1.a = 1; rec2.a = 100 |
+----------------------------+
1 row in set (0.19 sec)
Related Topics
- ROW: The
ROW()
function constructs aRECORD
object