ALTER VIRTUALTABLE

Purpose

Modifies a virtual table

Syntax

ALTER VIRTUALTABLE [<database>!]<virtualtable>

[CONNSTR <odbc_dsn_string>]

[ALIAS <aliasname>]

[TABLE <basetable>]

[KEYFIELDLIST <column-list>]

[PROPERTIES <properties_string>]

[AS <select statement>]

ALTER VIRTUALTABLE [<database>!]<virtualtable> ADDPROPERTY | MODIFYPROPERTY <properties_string>

ALTER VIRTUALTABLE [<database>!]<virtualtable> REMOVEPROPERTY <property>

See Also

ADD TABLE, ALTER INDEX, ALTER TABLE, CONSTRAINTS, COPY DATABASE, CREATE DATABASE, CREATE TABLE, CREATE VIRTUALTABLE, CursorAdapter, CURSORADAPTER(), DATA TYPES, DROP DATABASE, DROP TABLE, GETENV(), INSERT, OPEN DATABASE, SELECT, SET XMLFORMAT, TABLEINFO(), USE, Virtual Table Properties, Virtual Tables

Description

The ALTER VIRTUALTABLE command modifies a virtual table in the current database. Virtual tables exist in the database and are handled by CursorAdapters allowing remote/external ODBC data based on SQL SELECT statements to be treated as regular Lianja tables. Any code that references these tables e.g. USE <virtualtable> connects via the CursorAdapter and retrieves the data. Updates and deletes are handled transparently via the CursorAdapter. All CursorAdapters automatically use ODBC connection pooling against the same ODBC DSN to maximize performance.

ALTER VIRTUALTABLE can also be used as a synonym of CREATE VIRTUALTABLE, in which case the CONNSTR and AS clauses must be included.

Keywords	Description
database	The name of the database in which the virtual table should be created. The '!' character must be included between the database name and the virtual table name.
<virtualtable>	The name of the virtual table to be modified.

A combination of one or more of the following can be specified:

Keywords	Description
ALIAS <name>	The optional alias name for the virtual table.
CONNSTR <odbc_dsn_string>	The ODBC connection string. Specify 'local' or 'localhost' for a local Lianja database. At runtime, 'local' will be replaced by the connection string in the 'Runtime connection' App Setting; 'localhost' will not be replaced and will continue to use the local Lianja database. Note: if you are specifying a DSN that does not or cannot store the username and password details, the account information should be included here, e.g. 'mydsn;uid=myusername;pwd=mypassword'. If the virtual table was created without specifying a CONNSTR, the current SET CONNSTR value will be applied (from v4.1, previously was required).
TABLE <basetable>	The <basetable> is the name of the remote table. This is auto-detected from the AS <select statement>. If Lianja is unable to auto-detect the primary table from a complex SQL join statement (basetable error reported), the ALTER VIRTUALTABLE <virtualtable> TABLE <basetable> command should be run to specify this information for the virtual table.
KEYFIELDLIST <column-list>	The optional KEYFIELDLIST <column-list> specifies a comma separated list of columns e.g. "id,name" which are used to generate the WHERE clause for UPDATE and DELETE commands. For Lianja Cloud Server virtual table use, the virtual table must have a KEYFIELDLIST specified to provide a unique key for access and updates.
PROPERTIES <properties_string>	The <properties_string> is a ; separated list of name=value pairs corresponding to cursoradaptor properties. This therefore allows you to switch databases in the connection string.
AS <select statement>	The SQL SELECT statement.

Individual properties for the virtual table can be added using the ADDPROPERTY clause, modified using the MODIFYPROPERTY clause or removed using the REMOVEPROPERTY clause. See Virtual Table Properties.

Example

open database advworks
create virtualtable scurr connstr "awhr" as select * from sales.currency
alter virtualtable scurr connstr "awhr" as select name from sales.currency
 
// Modifying properties example
open datables sakdata
create virtualtable vt_actor connstr "sakila" keyfieldlist "actor_id" as select * from actor
alter virtualtable vt_actor addproperty "updatefieldlist=first_name"
alter virtualtable vt_actor modifyproperty "updatefieldlist=first_name, last_name"
alter virtualtable vt_actor removeproperty "updatefieldlist"
alter virtualtable vt_actor properties "updatefieldlist=last_name;keepalive=1"
alter virtualtable vt_actor properties ""