Replicating the SQL server SQL_VARIANT data type v7

The SQL_VARIANT data type defines a column so that the individual values in that column can have different data types. For example, the same SQL_VARIANT column can store values that were explicitly cast as character, integer, numeric, and date/time.

However, if a table containing a SQL_VARIANT column is to be replicated to a Postgres database, the usage of the column in Postgres is restricted to a single data type to which all the values in the SQL_VARIANT column are implicitly convertible (that is, without the use of explicit casting). For example, an integer value is implicitly convertible to a FLOAT data type, but a floating point value is not implicitly convertible to an INTEGER data type.

The following restrictions apply to using replication on tables with the SQL_VARIANT data type:

  • The values stored in the SQL_VARIANT columns of the table to be replicated must be implicitly convertible to the same data type in Postgres.
  • If there's more than one table with SQL_VARIANT columns to be replicated to the same Postgres database, then all such SQL_VARIANT columns must contain values that are implicitly convertible to the same data type in Postgres.

In the Postgres subscription database, you define a domain named sql_variant that maps to an underlying data type to which all values in the SQL_VARIANT columns are implicitly convertible.

The following example shows how to set up replication for a table containing a SQL_VARIANT data type used to store numeric values, but of different data types. The SQL Server table definition is the following:

CREATE TABLE variant_tbl (
    f1              INTEGER PRIMARY KEY,
    f2              SQL_VARIANT

INSERT INTO variant_tbl VALUES (1, CAST(1423.23 AS NUMERIC(6,2)));
INSERT INTO variant_tbl VALUES (2, CAST(8001 AS INTEGER));
INSERT INTO variant_tbl VALUES (3, CAST('4321' AS CHAR(4)));

The following query uses a function named SQL_VARIANT_PROPERTY to show the values stored in column f2 and their data types.

1> SELECT *,
2>     SQL_VARIANT_PROPERTY(f2,'BaseType') AS basetype,
3>     SQL_VARIANT_PROPERTY(f2,'Precision') AS precision,
4>     SQL_VARIANT_PROPERTY(f2,'Scale') AS scale
5> FROM variant_tbl;
6> GO
f1          f2         basetype   precision  scale
----------- ---------- ---------- ---------- ----------
          1 1423.23    numeric    6          2
          2 8001       int        10         0
          3 4321       char       0          0

(3 rows affected)

In the Postgres subscription database, create a domain named sql_variant with an underlying data type compatible with the values that are stored in the SQL Server SQL_VARIANT column:

CREATE DOMAIN sql_variant AS NUMERIC(6, 2);

After replication occurs, the subscription table is created using the sql_variant domain in place of the SQL_VARIANT data type of the publication table.