Using Caché SQL
Defining Tables
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This chapter describes how you create tables in Caché SQL. It discusses the following topics:

Table Names and Schema Names
You can create a table either by defining the table (using CREATE TABLE) or by defining a persistent class that is projected to a table:
The correspondence between these two names may not be identical for the following reasons:
Default Schema Name
The initial setting is to use the same default schema name for all namespaces (system-wide). You can set the same default schema name for all namespace, or set a default schema name for the current namespace.
If you create a table or other item with an unqualified name, Caché assigns it the default schema name, and the corresponding persistent class package name. If a named or default schema does not exist, Caché creates the schema (and package) and assigns the created item to the schema. If you delete the last item in a schema, Caché deletes the schema (and package). The following description of schema name resolution applies to table names, view names, and stored procedure names.
The initial system-wide default schema name is SQLUser. The corresponding persistent class package name is User. Therefore, either the unqualified table name Employee or the qualified table name SQLUser.Employee would generate the class User.Employee.
Because USER is a reserved word, attempting to specify a qualified name with the schema name of User (or any SQL Reserved Word) results in an SQLCODE -1 error.
To return the current default schema name, invoke the $SYSTEM.SQL.DefaultSchema() method:
  WRITE $SYSTEM.SQL.DefaultSchema()
Or use the following pre-processor macro:
#Include %occConstant
  WRITE $$$DefSchema
You can change the default schema name using either of the following:
When you change the default SQL schema name, the system automatically purges all cached queries in all namespaces on the system. By changing the default schema name, you change the meaning of all queries that contain unqualified table, view, or stored procedure names. It is strongly recommended that the default SQL schema name be established at Caché installation and not subsequently modified.
The schema name is used to generate the corresponding class package name. Because these names have different naming conventions, they may not be identical.
You can create a schema with the same name as an SQL reserved word by setting this as the system-wide Default Schema, though this is not recommended. A default schema named User generates the corresponding class package name Use0, following the class naming uniqueness convention.
Schema Search Path
When accessing an existing table (or view, or stored procedure) for a DML operation, an unqualified name is supplied the schema name from the schema search path. Schemas are searched in the order specified and the first match is returned. If no match is found in the schemas specified in the search path, or no search path exists, the default schema name is used. (Note that the #Import macro directive uses a different search strategy and does not “fall through” to the default schema name.)
If the unqualified name does not match any of the schemas specified in the schema search path or the default schema name, an SQLCODE -30 error is issued, such as the following: SQLCODE: -30 Message: Table 'PEOPLE' not found within schemas: CUSTOMERS,EMPLOYEES,SQLUSER.
Schema Naming Considerations
Schema names follow identifier conventions, with significant considerations concerning the use of non-alphanumeric characters. A schema name should not be specified as a delimited identifier. Attempting to specify “USER” or any other SQL reserved word as a schema name results in an SQLCODE -1 or -312 error. The INFORMATION_SCHEMA schema name and the corresponding INFORMATION.SCHEMA package name are reserved in all namespaces. Users should not create tables/classes within this schema/package.
When you issue a create operation, such as CREATE TABLE, that specifies a schema that does not yet exist, Caché creates the new schema. Caché uses the schema name to generate a corresponding package name. Because the naming conventions for schemas and their corresponding packages differ, the user should be aware of name conversion considerations for non-alphanumeric characters. These name conversion considerations are not the same as for tables:
Platform-Specific Schema Names
When creating an ODBC-based query to run from Microsoft Excel via Microsoft Query on the Mac, if you choose a table from the list of those available, the generated query does not include the table’s schema (equivalent to the package for a class). For example, if you choose to return all the rows of the Person table from the Sample schema (in the Samples namespace), the generated query is:
Because Caché interprets an unqualified table name as being in the SQLUser schema, this statement either fails or returns data from the wrong table. To correct this, edit the query (on the SQL View tab) to explicitly refer to the desired schema. The query should then be:
SELECT * FROM Sample.Person
Table Naming Considerations
Every table has a unique name within its schema. A table has both an SQL table name and a corresponding persistent class name; these names differ in permitted characters, case-sensitivity, and maximum length. If defined using the SQL CREATE TABLE command, you specify an SQL table name that follows identifier conventions; the system generates a corresponding persistent class name. If defined as a persistent class definition, you must specify a name that contains only alphanumeric characters; this name is used as both the case-sensitive persistent class name and (by default) the corresponding non-case-sensitive SQL table name. The optional SqlTableName class keyword allows the user to specify a different SQL table name.
When you use the CREATE TABLE command to create a table, Caché uses the table name to generate a corresponding persistent class name. Because the naming conventions for tables and their corresponding classes differ, the user should be aware of name conversion considerations for non-alphanumeric characters:
Attempting to specify “USER” or any other SQL reserved word as a table name or schema name results in an SQLCODE -312 error. To specify an SQL reserved word as a table name or schema name, you can specify the name as a delimited identifier. If you use a delimited identifier to specify a table or schema name that contains non-alphanumeric characters, Caché strips out these non-alphanumeric characters when generating the corresponding class or package name.
The following table name length limits apply:
For further details on table names, refer to the CREATE TABLE command in the Caché SQL Reference. For further details, on classes refer to Caché Classes in the Using Caché Objects manual.
RowID Field
In SQL, every record is identified by a unique integer value, known as the RowID. In InterSystems SQL you do not need to specify a RowID field. When you create a table and specify the desired data fields, a RowID field is automatically created. This RowID is used internally, but is not mapped to a class property. By default, its existence is only visible when a persistent class is projected to an SQL table. In this projected table, an additional RowID field appears. By default, this field is named "ID" and is assigned to column 1.
By default, when a table is populated with data, Caché assigns sequential positive integers to this field, starting with 1. The RowID data type is BIGINT (%Library.BigInt). The values generated for the RowID have the following constraints: Each value is unique. The NULL value is not permitted. Collation is EXACT. By default, values are not modifiable.
By default, Caché names this field “ID”. However this field name is not reserved. The RowID field name is re-established each time the table is compiled. If the user defines a field named “ID”, when the table is compiled Caché names the RowID as “ID1”. If, for example, the user then uses ALTER TABLE to define a field named “ID1”, the table compile renames the RowID as “ID2”, and so forth. In a persistent class definition you can use the SqlRowIdName class keyword to directly specify the RowID field name for the table to which this class is projected. For these reasons, referencing the RowID field by name should be avoided.
Caché SQL provides the %ID pseudo-column name (alias) which always returns the RowID value, regardless of the field name assigned to the RowID. (Caché TSQL provides the $IDENTITY pseudo-column name, which does the same thing.)
ALTER TABLE cannot modify or delete the RowID field definition.
When records are inserted into the table, Caché assigns each record an integer ID value. By default, Caché performs ID assignment using $SEQUENCE, allowing for the rapid simultaneous populating of the table by multiple processes. You can configure Caché to perform ID assignment using $INCREMENT by setting the SetDDLUseSequence() method; to determine the current setting, call the $SYSTEM.SQL.CurrentSettings() method.
RowID values always increment. They are not reused. Therefore, if the table data has been inserted by multiple processes and/or modified by delete and insert operations, the RowID values will be in ascending numeric sequence (the order of insert), but will not be numerically contiguous. In a persistent class definition, the IdLocation storage keyword <IdLocation>^Sample.PersonD</IdLocation> global contains the highest assigned value of the RowID counter. To determine if a specific RowID value exists, invoke the table’s %ExistsId() method.
The RowID counter is reset by the TRUNCATE TABLE command. It is not reset by a DELETE command, even when the DELETE command deletes all rows in the table. If no data has been inserted into the table, or TRUNCATE TABLE has been used to delete all table data, the ^Sample.PersonD global is undefined.
By default, RowID values are not user-modifiable. Modifying RowID values can have serious consequences and should only be done in very specific cases and with extreme caution. The Config.SQL.AllowRowIDUpdate property allows RowID values to be user-modifiable.
RowID Based on Fields
By defining a persistent class that projects a table, you can define the RowID to have values from a field or a combination of fields. To do this, specify an index with the IdKey index keyword. For example, a table can have a RowID whose values are the same as the values of the PatientName field by specifying the index definition IdxId On PatientName [IdKey];, or the combined values of the PatientName and SSN fields by specifying the index definition IdxId On (PatientName,SSN) [IdKey];.
When a RowID is based on multiple fields, the RowID value is the values of each of its component fields joined by the || operator. For example, Ross,Betsy||123-45-6789. The maximum length of a RowID that is based on multiple fields defaults to 254.
For further details, refer to Primary Key.
RowID Hidden?
By default, the RowID is hidden (not displayed by SELECT *) and PRIVATE. When you create a table you can specify the %PUBLICROWID keyword to make the RowID not hidden and public. Because this keyword specifies that the table’s RowID is PUBLIC, the RowID can therefore be used as a foreign key reference. If you specify the %PUBLICROWID keyword, the persistent class corresponding to the table is defined with the class keyword Not SqlRowIdPrivate. This optional %PUBLICROWID keyword can be specified anywhere in the CREATE TABLE comma-separated list of table elements. It cannot be specified in ALTER TABLE. For further details, refer to The RowID Field and %PUBLICROWID in the CREATE TABLE reference page.
You can display whether the RowID is hidden using the Management Portal SQL interface Catalog Details Fields listing Hidden column.
You can use the following program to return whether a specified field (in this example, ID) is hidden:
  SET tStatement = ##class(%SQL.Statement).%New()
  SET qStatus = tStatement.%Prepare(myquery)
   IF qStatus'=1 {WRITE "%Prepare failed:" DO $System.Status.DisplayError(qStatus) QUIT}
  SET rset = tStatement.%Execute()
  DO rset.%Display()
  WRITE !,"End of data" 
To list the field names (hidden and non-hidden) in a table, refer to Column Names and Numbers.
Primary Key
Caché provides two ways to uniquely identify a row in a table: the RowID and the Primary Key.
The optional primary key is a meaningful value an application can use to uniquely identify a row in the table (for example in joins). A primary key can be user-specified data field or can be a combination of more than one data fields. Primary key values must be unique, but are not required to be integer values. The RowID is an integer value used internally to identify a row in the table. Often the primary key is a value generated by the application, while the RowID is a unique integer value generated by Caché.
The system automatically creates a Master Map to access rows of data using the RowID field. If you define a primary key field, the system automatically creates and maintains a primary key index.
Obviously, the duality of having two different fields and indexes to identify rows might not necessarily be a good thing. You can resolve to a single row identifier and index in either of two ways:
Depending on the nature of the application, you may wish to resolve to a single row identifier and index or to have separate indexes for the application-generated primary key and the system-generated RowID.
RowVersion and Serial Counter Fields
InterSystems SQL supports two special-purpose data types for automatically-incrementing counter values:
RowVersion Field
The RowVersion field is an optional user-defined field that provides row-level version control, allowing you to determine the order in which changes were made to the data in each row namespace-wide. Caché maintains a namespace-wide counter, and assigns a unique incremental positive integer to this field each time the row data is modified (insert, update, or %Save). Because this counter is namespace-wide, an operation on one table with a ROWVERSION field sets the increment point for the ROWVERSION counter that is used for all other tables with a ROWVERSION field in the same namespace.
You create a RowVersion field by specifying a field of data type ROWVERSION. You can only specify one ROWVERSION data type field per table. Attempting to create a table with more than one ROWVERSION field results in a 5320 compilation error.
This field can have any name and can appear in any column position. The ROWVERSION (%Library.RowVersion) data type maps to BIGINT (%Library.BigInt).
This field receives a positive integer from an automatically incremented counter, starting with 1. This counter increments whenever data in any ROWVERSION-enabled table is modified by an insert, update, or %Save operation. The incremented value is recorded in the ROWVERSION field of the row that has been inserted or updated.
A namespace can contain tables with a RowVersion field and tables without this field. Only data changes to tables that have a RowVersion field increment the namespace-wide counter.
When a table is populated with data, Caché assigns sequential integers to this field for each inserted row. If you use ALTER TABLE to add a ROWVERSION field to a table that already contains data, this field is created as NULL for pre-existing fields. Any subsequent insert or update to the table assigns a sequential integer to the RowVersion field for that row. This field is read-only; attempting to modify a RowVersion value generates an SQLCODE -138 error: Cannot INSERT/UPDATE a value for a read only field. Therefore, a RowVersion field is defined as unique and non-modifible, but not required or non-null.
RowVersion values always increment. They are not reused. Therefore, inserts and updates assign unique RowVersion values in temporal sequence. Delete operations remove numbers from this sequence. Therefore, RowVersion values may not be numerically contiguous.
This counter is never reset. Deleting all table data does not reset the RowVersion counter. Even dropping all tables in the namespace that contain a ROWVERSION field does not reset this counter.
The RowVersion field should not be included in a unique key or primary key. The RowVersion field cannot be part of an IDKey index.
The RowVersion field is not hidden (it is displayed by SELECT *).
This is shown in the following example of three tables in the same namespace.
  1. Create Table1 and Table3, each of which has a ROWVERSION field, and Table2 that does not have a ROWVERSION field.
  2. Insert ten rows into Table1. The ROWVERSION values of these rows are the next ten counter increments. Since the counter has not previously been used, they are 1 through 10.
  3. Insert ten rows into Table2. Because Table2 does not have a ROWVERSION field, the counter is not incremented.
  4. Update a row of Table1. The ROWVERSION values for this row is changed to the next counter increment (11 in this case).
  5. Insert ten rows into Table3. The ROWVERSION values of these rows are the next ten counter increments (12 through 21).
  6. Update a row of Table1. The ROWVERSION values for this row is changed to the next counter increment (22 in this case).
  7. Delete a row of Table1. The ROWVERSION counter is unchanged.
  8. Update a row of Table3. The ROWVERSION values for this row is changed to the next counter increment (23 in this case).
Serial Field
You can use the SERIAL data type (%Library.Counter in a persistent class table definition) to specify one or more optional integer counter fields to record the order of inserts of records into a table. By default, this field receives a positive integer from an automatically incremented table counter whenever a row is inserted into the table. However, a user can specify an integer value for this field during an insert, overriding the table counter default.
Attempting to UPDATE a counter field value results in an SQLCODE -105 error.
This counter is reset to 1 by the TRUNCATE TABLE command. It is not reset by a DELETE command, even when the DELETE command deletes all rows in the table.
Defining a Table by Creating a Persistent Class
The primary way to define tables within Caché is to use Studio to create persistent class definitions. When these classes are saved and compiled within the Caché database, they automatically projects to a relational table that corresponds to the class definition: each class represents a table; each property represents a column, and so on. The maximum number of properties (columns) definable for a class (table) is 1000.
For example, the following defines the persistent class MyApp.Person:
Class MyApp.Person Extends %Persistent 
Property Name As %String(MAXLEN=50) [Required];
Property SSN As %String(MAXLEN=15) [InitialExpression = "Unknown"];
Property DateOfBirth As %Date;
Property Sex As %String(MAXLEN=1);
When compiled, this creates the MyApp.Person persistent class and the corresponding SQL table, Person within the MyApp schema. For details on how to perform these operations, refer to Defining and Compiling Classes in the Defining and Using Classes manual.
In this example, the package name MyApp is specified. When defining a persistent class, an unspecified package name defaults to User; this corresponds to the default SQL schema name SQLUser. For example, defining a table named Students as a persistent class creates the class User.Students, and the corresponding SQL schema.table name SQLUser.Students.
In this example, the persistent class name Person is the default SQL table name. You can use the SqlTableName class keyword to supply a different SQL table name.
The same MyApp.Person table could have been defined using the DDL CREATE TABLE statement, specifying the SQL schema.table name. Successful execution of this SQL statement generates a corresponding persistent class with package name MyApp and class name Person:
    Name VARCHAR(50) NOT NULL,
    SSN VARCHAR(15) DEFAULT 'Unknown',
    DateOfBirth DATE,
    Sex VARCHAR(1)
CREATE TABLE does not specify an explicit StorageStrategy in the corresponding class definition. It instead takes the defined default storage strategy.
By default, CREATE TABLE specifies the Final class keyword in the corresponding class definition, indicating that it cannot have subclasses.
For an introduction to how the object view of the database corresponds to the relational view, see Introduction to the Default SQL Projection in the chapter “Introduction to Persistent Objects” of Using Caché Objects.
Note that a persistent class definition such as the one shown above creates the corresponding table when it is compiled, but this table definition cannot be modified or deleted using SQL DDL commands (or by using the Management Portal Drop action), which give you the message “DDL not enabled for class ''...”). You must specify [DdlAllowed] in the table class definition to permit these operations:
Class MyApp.Person Extends %Persistent [DdlAllowed]
You can specify %Populate in the class definition to enable automatic populating of the table with test data.
Class MyApp.Person Extends (%Persistent,%Populate) [DdlAllowed]
This provides a Populate() method for the class. Running this method populates the table with ten rows of test data.
Enumerated Property Values
Defining at table as a persistent class allows you to define properties (fields) that can only contain certain specified values. This is done by specifying the VALUELIST parameter, as shown in the following example:
Class MyApp.Person Extends %Persistent 
Property Name As %String(MAXLEN=50) [Required];
Property DateOfBirth As %Date;
Property Sex As %String(VALUELIST=",M,F");
If VALUELIST is specified, an INSERT or UPDATE can only specify one of the values listed in VALUELIST, or be provided with no value (NULL). VALUELIST valid values are case-sensitive. Specifying a data value that doesn’t match the VALUELIST values results in a field value failed validation error: SQLCODE -104 for INSERT or SQLCODE -105 for UPDATE.
CREATE TABLE does not provide this functionality.
Unique Values
CREATE TABLE allows you to define a field as UNIQUE. This means that every field value is a unique (non-duplicate) value.
Defining at table as a persistent class does not support a corresponding property keyword. Instead, you must define both the property and a unique index on that property. The following example provides for a unique Num value for each record.
  Class Sample.CaveDwellers Extends %Persistent [ DdlAllowed ]
  Property Num As %Integer;
  Property Troglodyte As %String(MAXLEN=50);
  Index UniqueNumIdx On Num [ Type=index,Unique ];
The index name follows the naming conventions for properties. The optional Type keyword specifies the index type. The Unique keyword defines the property (field) as unique.
Having a unique value field is necessary for using the INSERT OR UPDATE statement.
Computed Values
The following class definition example defines a table that includes a field (Birthday) that uses SqlComputed to compute its value when you initially set the DateOfBirth field value and SqlComputeOnChange to recompute its value when you update the DateOfBirth field value. The Birthday field value includes the current timestamp to record when this field value was computed/recomputed:
Class Sample.MyStudents Extends %Persistent [DdlAllowed]
  Property Name As %String(MAXLEN=50) [Required];
  Property DateOfBirth As %Date;
  Property Birthday As %String 
          [ SqlComputeCode = {SET {Birthday}=$PIECE($ZDATE({DateOfBirth},9),",")_
                              " changed: "_$ZTIMESTAMP},
                              SqlComputed, SqlComputeOnChange = DateOfBirth ];
Note that an UPDATE to DateOfBirth that specifies the existing DateOfBirth value does not recompute the Birthday field value. For the corresponding SQL code, refer to the COMPUTECODE section of the CREATE TABLE reference page.
For reference material on class property keywords, refer to the Property Keywords chapter of Caché Class Definition Reference.
Embedded Object (%SerialObject)
You can simplify the structure of a persistent table by referencing an embedded serial object class that defines properties. For example, you want the MyData.Person to contain address information, consisting of street, city, state, and postal code. Rather than specifying these properties in MyData.Person, you can define a serial object (%SerialObject) class that defines these properties, and then in MyData.Person specify a single Home property that references that embedded object. This is shown in the following class definitions:
Class MyData.Person Extends (%Persistent) [ DdlAllowed ]
{  Property Name As %String(MAXLEN=50);
   Property Home As MyData.Address;
   Property Age As %Integer;
Class MyData.Address Extends (%SerialObject)
{  Property Street As %String;
   Property City As %String;
   Property State As %String;
   Property PostalCode As %String;
You cannot access the data in a serial object property directly, you must access them through a persistent class/table that references it:
Note that an embedded serial object does not have to be in the same package as the persistent table that references it.
Defining embedded objects can simplify persistent table definitions:
For further details, refer to Introduction to Serial Objects in Defining and Using Classes.
For information on creating an index for a serial object property, refer to Indexing an Embedded Object (%SerialObject) Property.
Class Methods
You can specify class methods as part of a table definition, as shown in the following example:
Class MyApp.Person Extends %Persistent 
Property Name As %String(MAXLEN=50) [Required];
Property SSN As %String(MAXLEN=15) [InitialExpression = "Unknown"];
Property DateOfBirth As %Date;
Property Sex As %String(MAXLEN=1);
ClassMethod Numbers() As %Integer [ SqlName = Numbers, SqlProc ]
   QUIT 123
In a SELECT query you can invoke this method as follows:
SELECT Name,SSN,MyApp.Numbers() FROM MyApp.Person
Defining a Table by Using DDL
You can define tables in Caché SQL using standard DDL commands:
Available DDL Commands in Caché SQL
ALTER Commands CREATE Commands DROP Commands
These are described in the Caché SQL Reference.
You can execute DDL commands in a variety of ways, including:
Using DDL in Embedded SQL
Within an ObjectScript method or routine, you can use embedded SQL to invoke DDL commands.
For example, the following method creates a TEST.EMPLOYEE table:
ClassMethod CreateTable() As %Integer
    EMPNUM              INT NOT NULL,
    NAMELAST            CHAR (30) NOT NULL,
    NAMEFIRST           CHAR (30) NOT NULL,
    SALARY              MONEY,
 Write "SQL: ",SQLCODE,!
When this method is invoked it attempts to create a TEST.EMPLOYEE table (as well as the corresponding TEST.EMPLOYEE class). If successful, the SQLCODE variable is set to 0. If unsuccessful, SQLCODE contains an SQL Error Code indicating the reason for the failure.
The most common reasons that a DDL command such as this one will fail are:
Using a Class Method to Execute DDL
Within ObjectScript or Caché Basic, you can use the Dynamic SQL %SQL.Statement object to prepare and execute DDL commands using Dynamic SQL.
The following example defines a class method to create a table using Dynamic SQL:
  Class Sample.NewT
  ClassMethod DefTable(user As %String,pwd As %String) As %Status [Language=cache]
    DO ##class(%SYSTEM.Security).Login(user,pwd)
    SET myddl=2
    SET myddl(1)="CREATE TABLE Sample.MyTest "
    SET tStatement=##class(%SQL.Statement).%New()
    SET tStatus=tStatement.%Prepare(.myddl)
      IF qStatus'=1 {WRITE "%Prepare failed:" DO $System.Status.DisplayError(qStatus) QUIT}
    SET rset=tStatement.%Execute()
    IF rset.%SQLCODE=0 {WRITE "Created a table"}
    ELSEIF rset.%SQLCODE=-201 {WRITE "table already exists"}
    ELSE {WRITE "Unexpected error SQLCODE=",rset.%SQLCODE}
This method is invoked as follows:
  DO ##class(Sample.NewT).DefTable("myname","mycachepassword")
As with the embedded SQL example, this method will fail if there is no current user logged in.
Defining Tables by Importing and Executing a DDL Script
You can import Caché SQL DDL script files using either the Cache() method interactively from a Terminal session, or the DDLImport("CACHE") method as a background job. This method can import and execute multiple SQL commands, enabling you to use a txt script file to define tables and views and populate them with data. For further details, refer to the Importing SQL Code chapter of this guide.
If you are migrating tables from another vendor’s relational database to Caché, you may have one or more DDL scripts within text files. Caché provides several %SYSTEM.SQL methods to help load such DDL scripts into Caché. You can use the general-purpose DDLImport() method, or the %SYSTEM.SQL method for the specific vendor. The vendor-specific SQL is converted to Caché SQL and executed. Errors and unsupported features are recorded in log files. For further details, refer to the Code Migration: Importing non-Caché SQL in the “Importing SQL Code” chapter of this guide.
For example, to load an Oracle DDL file from the Caché command line:
  1. Start a Terminal session using the Terminal command in the “Caché Cube” menu.
  2. Switch to the namespace in which you wish to load the table definitions:
  3. Invoke the desired DDL import method:
     DO $SYSTEM.SQL.Oracle()
    and follow the directions displayed at the terminal.
Defining a Table by Querying an Existing Table
You can use the $SYSTEM.SQL.QueryToTable() method to define and populate a new table based on an existing table. You specify a query and a new table name. The existing table name and/or the new table name can be qualified or unqualified. The query can contain JOIN syntax. The query can supply column name aliases that become the column names in the new table.
  1. QueryToTable() copies the DDL definition of a existing table and assigns it the specified new table name. It copies the definitions of the fields specified in the query, including the data type, maxlength, and minval/maxval. It does not copy field data constraints, such as default value, required value, or unique value.
    If the query specifies SELECT * or SELECT %ID, the RowID field of the original table is copied as a non-required, non-unique data field of data type integer. QueryToTable() generates a unique RowID field for the new table. If the copied RowID is named ID, the generated RowID is named ID1.
    QueryToTable() creates a corresponding persistent class for this new table. The persistent class is defined as DdlAllowed. The owner of the new table is the current user.
    The new table is defined with %Cache storage = YES and Supports Bitmap Indices = YES, regardless of these settings in the source table.
    The only index created for the new table is the IDKEY index. No bitmap extent index is generated. Index definitions for the copied fields are not copied into the new table.
    References from a field to another table are not copied.
  2. QueryToTable() then populates the new table with data from the fields selected by the query. It sets the table’s Extent Size to 100,000. It estimates the IDKEY Block Count. Run Tune Table to set the actual Extent Size and Block Count, and the Selectivity and Average Field Size values for each field.
QueryToTable() both creates a table definition and populates the new table with data. If you wish to only create a table definition, specify a condition in the query WHERE clause that selects for no data rows. For example, WHERE Age < 20 AND Age > 20.
The following example copies the Name, and Age, fields from Sample.Person and creates an AVG(Age) field. These field definitions are used to create a new table named Sample.Youth. The method then Populates Sample.Youth with the Sample.Person data for those records where Age < 21. The AvgInit field contains the aggregate value for the selected records at the time that the table was created.
  DO $SYSTEM.SQL.QueryToTable("SELECT Name,Age,AVG(Age) AS AvgInit FROM Sample.Person WHERE Age < 21","Sample.Youth",1,.errors)
External Tables
In Caché SQL, you can also have “external tables,” tables that are defined within the Caché dictionary but are stored within an external relational database. External tables act as if they were native Caché tables: you can issue queries against them and perform INSERT, UPDATE, and DELETE operations. The access to external database is provided by the Caché SQL Gateway, which offers transparent connectivity using ODBC or JDBC. See Using the Caché SQL Gateway for more details.
Listing Tables
The INFORMATION.SCHEMA.TABLES persistent class displays information about all tables (and views) in the current namespace. It provides a number of properties including the schema and table names, the owner of the table, and whether you can insert new records.
The following example returns the table type, schema name, table name, and owner for all tables and views in the current namespace:
You can display much of the same information as INFORMATION.SCHEMA.TABLES for a single table using the Catalog Details tab in the Management Portal SQL Interface.
Listing Column Names and Numbers
You can list all of the column names (field names) for a specified table in three ways:
The GetColumns() Method
To list the names of the columns in a table in column number order, you can use the GetColumns() method, as follows:
  SET stat=##class(%SYSTEM.SQL).GetColumns("Sample.Person",.byname,.bynum)
  IF stat=1 {
    SET i=1
    WHILE $DATA(bynum(i)) { WRITE "name is ",bynum(i),"   col num is ",i,!
                            SET i=i+1 }
  ELSE { WRITE "GetColumns() cannot locate specified table" }
GetColumns() lists all defined columns, including hidden columns. If a table references an embedded %SerialObject class, GetColumns() first lists all of the columns in the persistent class, including the property that references the %SerialObject, then lists all of the %SerialObject properties. This is shown in the following GetColumns() results:
name is ID   col num is 1
name is Age   col num is 2
name is Home   col num is 3
name is Name   col num is 4
name is x__classname   col num is 5
name is Home_City   col num is 6
name is Home_Phone   col num is 7
name is Home_Phone_AreaCode   col num is 8
name is Home_Phone_Country   col num is 9
name is Home_Phone_TNum   col num is 10
name is Home_PostalCode   col num is 11
name is Home_State   col num is 12
name is Home_Street   col num is 13
You can also use this method to determine the column number for a specified column name, as follows:
  SET stat=##class(%SYSTEM.SQL).GetColumns("Sample.Person",.byname)
  IF stat=1 {
         WRITE "Home_State is column number ",byname("Home_State"),!  }
  ELSE { WRITE "GetColumns() cannot locate specified table" }

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