User-Defined Types - SQL Server to Aurora MySQL Migration Playbook
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User-Defined Types

Feature compatibility Amazon SCT / Amazon DMS automation level Amazon SCT action code index Key differences


                              Three star feature compatibility


                              Three star automation level

User-Defined Types

Replace scalar UDT with base types. Rewrite stored procedures that use table-type input parameters to use strings with CSV, XML, or JSON, or to process row-by-row. For more information, see Stored Procedures.

SQL Server Usage

SQL Server user-defined types provide a mechanism for encapsulating custom data types and for adding NULL constraints.

SQL Server also supports table-valued user-defined types, which you can use to pass a set of values to a stored procedure.

User defined types can also be associated to CLR code assemblies. Beginning with SQL Server 2014, memory-optimized types support memory optimized tables and code.

Note

If your code uses custom rules bound to data types, Microsoft recommends discontinuing use of this deprecated feature.

All user-defined types are based on an existing system data types. They allow developers to reuse the definition, making the code and schema more readable.

Syntax

The simplified syntax for the CREATE TYPE statement.

CREATE TYPE <type name> {
FROM <base type> [ NULL | NOT NULL ] | AS TABLE (<Table Definition>)}

Examples

User-defined types

Create a ZipCodeScalar user-defined type.

CREATE TYPE ZipCode
FROM CHAR(5)
NOT NULL

Use the ZipCodetype in a table.

CREATE TABLE UserLocations
(UserID INT NOT NULL PRIMARY KEY, ZipCode ZipCode);
INSERT INTO [UserLocations] ([UserID],[ZipCode]) VALUES (1, '94324');
INSERT INTO [UserLocations] ([UserID],[ZipCode]) VALUES (2, NULL);

For the preceding example, the following error message appears. It indicates that NULL values for ZipCodeare aren’t allowed.

Msg 515, Level 16, State 2, Line 78
Cannot insert the value NULL into column 'ZipCode', table 'tempdb.dbo.UserLocations';
column doesn't allow nulls. INSERT fails.
The statement has been terminated.

Table-valued types

The following example demonstrates how to create and use a table valued types to pass a set of values to a stored procedure.

Create the OrderItems table.

CREATE TABLE OrderItems
(
    OrderID INT NOT NULL,
    Item VARCHAR(20) NOT NULL,
    Quantity SMALLINT NOT NULL,
    PRIMARY KEY(OrderID, Item)
);

Create a table valued type for the OrderItems table.

CREATE TYPE OrderItems
AS TABLE
(
    OrderID INT NOT NULL,
    Item VARCHAR(20) NOT NULL,
    Quantity SMALLINT NOT NULL,
    PRIMARY KEY(OrderID, Item)
);

Create the InsertOrderItems procedure. Note that the entire set of rows from the table valued parameter is handled with one statement.

CREATE PROCEDURE InsertOrderItems
@OrderItems AS OrderItems READONLY
AS
BEGIN
    INSERT INTO OrderItems(OrderID, Item, Quantity)
    SELECT OrderID,
        Item,
        Quantity
    FROM @OrderItems;
END

Instantiate the OrderItems type, insert the values, and pass it to a stored procedure.

DECLARE @OrderItems AS OrderItems;
INSERT INTO @OrderItems ([OrderID], [Item], [Quantity])
VALUES
(1, 'M8 Bolt', 100),
(1, 'M8 Nut', 100),
(1, M8 Washer, 200);

EXECUTE [InsertOrderItems] @OrderItems = @OrderItems;

(3 rows affected)

Select all rows from the OrderItems table.

SELECT * FROM OrderItems;

OrderID  Item       Quantity
1        M8 Bolt    100
1        M8 Nut     100
1        M8 Washer  200

For more information, see CREATE TYPE (Transact-SQL) in the SQL Server documentation.

MySQL Usage

Amazon Aurora MySQL-Compatible Edition (Aurora MySQL) 5.7 doesn’t support user defined types and user defined table valued parameters.

The current documentation doesn’t indicate these features will be supported in Aurora MySQL version 8.

Migration Considerations

For scalar user-defined types, replace the type name with base type and optional NULL constraints.

For table-valued user-defined types used as stored procedure parameters, the workaround is more complicated.

Common solutions include using either temporary tables to hold the data or passing large string parameters containing the data in CSV, XML, JSON (or any other convenient format) and then writing code to parse these values in a stored procedure. Alternatively, if the logic doesn’t require access to the entire set of changes, and for small data sets, it is easier to call the stored procedure in a loop and pass the columns as standard parameters, row by row.

Memory-optimized engines aren’t yet supported in Aurora MySQL. You must convert memory optimized tables to disk based tables.

Examples

Replacing a user-defined type

Replace the ZipCode user-defined type with a base type.

CREATE TABLE UserLocations
(
    UserID INT NOT NULL
    PRIMARY KEY,
    /*ZipCode*/ CHAR(5) NOT NULL
);

Replacing a table-valued stored procedure parameter

The following steps describe how to replace a table-valued parameter with a source table and a LOOP cursor.

Create an OrderItems table.

CREATE TABLE OrderItems
(
    OrderID INT NOT NULL,
    Item VARCHAR(20) NOT NULL,
    Quantity SMALLINT NOT NULL,
    PRIMARY KEY(OrderID, Item)
);

Create and populate the SourceTable.

CREATE TABLE SourceTable
(
    OrderID INT,
    Item VARCHAR(20),
    Quantity SMALLINT,
    PRIMARY KEY (OrderID, Item)
);
INSERT INTO SourceTable (OrderID, Item, Quantity)
VALUES
(1, 'M8 Bolt', 100),
(2, 'M8 Nut', 100),
(3, 'M8 Washer', 200);

Create a procedure to loop through the SourceTable and insert rows.

Note

There are syntax differences from T-SQL for both the CREATE PROCEDURE and the CURSOR declaration and use. For more information, see Stored Procedures and Cursors.

CREATE PROCEDURE LoopItems()
BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE var_OrderID INT;
    DECLARE var_Item VARCHAR(20);
    DECLARE var_Quantity SMALLINT;
    DECLARE ItemCursor CURSOR
        FOR SELECT OrderID,
            Item,
            Quantity
        FROM SourceTable;
    DECLARE CONTINUE HANDLER
        FOR NOT FOUND
        SET done = TRUE;
    OPEN ItemCursor;
    CursorStart: LOOP
    FETCH NEXT FROM ItemCursor
        INTO var_OrderID, var_Item, var_Quantity;
    IF Done
        THEN LEAVE CursorStart;
    END IF;
        INSERT INTO OrderItems (OrderID, Item, Quantity)
        VALUES (var_OrderID, var_Item, var_Quantity);
    END LOOP;
    CLOSE ItemCursor;
END;

Call the stored procedure.

CALL LoopItems();

Select all rows from the OrderItems table.

SELECT * FROM OrderItems;

OrderID  Item       Quantity
1        M8 Bolt    100
2        M8 Nut     100
3        M8 Washer  200

Summary

SQL Server Aurora MySQL Comments

Table-valued parameters

Not supported

Use either temporary tables, or CSV, XML, JSON string parameters and parse the data. Alternatively, rewrite the stored procedure to accept the data one row at a time and process the data in a loop.

Memory-optimized table-valued user-defined types

Not supported

Not supported.

For more information, see Cursors in the MySQL documentation.