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Composing Update SQL Statements
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At design time, you can use the Update SQL editor to write the SQL statements for the DeleteSQL, InsertSQL, and ModifySQL properties. If you do not use the Update SQL editor, or if you want to modify the generated statements, you should keep in mind the following guidelines when writing statements to delete, insert, and modify records in the base table.

The DeleteSQL property should contain only an SQL statement with the DELETE command. The base table to be updated must be named in the FROM clause. So that the SQL statement only deletes the record in the base table that corresponds to the record deleted in the update cache, use a WHERE clause. In the WHERE clause, use a parameter for one or more fields to uniquely identify the record in the base table that corresponds to the cached update record. If the parameters are named the same as the field and prefixed with "OLD_", the parameters are automatically given the values from the corresponding field from the cached update record. If the parameter are named in any other manner, you must supply the parameter values.

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    DELETE FROM Inventory I
    WHERE (I.ItemNo = :OLD_ItemNo)

Some table types might not be able to find the record in the base table when fields used to identify the record contain NULL values. In these cases, the delete update fails for those records. To accommodate this, add a condition for those fields that might contain NULLs using the IS NULL predicate (in addition to a condition for a non-NULL value). For example, when a FirstName field may contain a NULL value:

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    DELETE FROM Names
    WHERE (LastName = :OLD_LastName) AND
      ((FirstName = :OLD_FirstName) OR (FirstName IS NULL))

The InsertSQL statement should contain only an SQL statement with the INSERT command. The base table to be updated must be named in the INTO clause. In the VALUES clause, supply a comma-separated list of parameters. If the parameters are named the same as the field, the parameters are automatically given the value from the cached update record. If the parameter are named in any other manner, you must supply the parameter values. The list of parameters supplies the values for fields in the newly inserted record. There must be as many value parameters as there are fields listed in the statement.

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    INSERT INTO Inventory
    (ItemNo, Amount)
    VALUES (:ItemNo, 0)

The ModifySQL statement should contain only an SQL statement with the UPDATE command. The base table to be updated must be named in the FROM clause. Include one or more value assignments in the SET clause. If values in the SET clause assignments are parameters named the same as fields, the parameters are automatically given values from the fields of the same name in the updated record in the cache. You can assign additional field values using other parameters, as long as the parameters are not named the same as any fields and you manually supply the values. As with the DeleteSQL statement, supply a WHERE clause to uniquely identify the record in the base table to be updated using parameters named the same as the fields and prefixed with "OLD_". In the update statement below, the parameter :ItemNo is automatically given a value and :Price is not.

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    UPDATE Inventory I
    SET I.ItemNo = :ItemNo, Amount = :Price
    WHERE (I.ItemNo = :OLD_ItemNo)

Considering the above update SQL, take an example case where the application end-user modifies an existing record. The original value for the ItemNo field is 999. In a grid connected to the cached dataset, the end-user changes the ItemNo field value to 123 and Amount to 20. When the ApplyUpdates method is invoked, this SQL statement affects all records in the base table where the ItemNo field is 999, using the old field value in the parameter :OLD_ItemNo. In those records, it changes the ItemNo field value to 123 (using the parameter :ItemNo, the value coming from the grid) and Amount to 20.

See Also

Understanding Parameter Substitution in Update SQL Statements

Creating SQL Statements at Design Time

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