%SQL.Statement
class %SQL.Statement extends %Library.RegisteredObject [ Final ]
For details on using this class, see Using Dynamic SQL.
The sample class mentioned here (Sample.Person) is part of https://github.com/intersystems/Samples-Data.Opens in a new tab See Downloading SamplesOpens in a new tab.
%SQL.Statement implements an interface to prepare and execute dynamic SQL statements.
Dynamic SQL
The %SQL.Statement class implements an interface for managing dynamic SQL statements. The interface consists of the %Prepare(), %Execute(), %ExecDirect() methods and the %Dialect, %Metadata, %SchemaPath, and %SelectMode properties.
To prepare and execute a dynamic SQL statement, use an instance of %SQL.Statement, such as:
set tStatement = ##class(%SQL.Statement).%New(2,"Sample")
%New() accepts three optional parameters as follows: %New(selectmode,schemapath,dialect) where selectmode is one of the allowed values of the %SelectMode property of this class, schemapath is one of the allowed values of the %SchemaPath property of this class, and dialect is one of the allowed values of the %Dialect property of this class. You can explicitly set these properties at any time; the value of each affects subsequent statement preparation and execution.
Next, prepare the dynamic statement by invoking the %Prepare() method. %Prepare() accepts an SQL statement in the form of a simple value or in an array passed by reference. For an array, the value of the base node is the number of lines in the array and each node’s subscript specifies its line number; the value of each subnode is a portion of the SQL statement. An example of preparing an array is:
set tSQL = 3 set tSQL(1) = "select %ID as id, Name, DOB, Home_State" set tSQL(2) = "from Person where Age > 80" set tSQL(3) = "order by 2" set tStatus = tStatement.%Prepare(.tSQL)
%Prepare() returns a status value that indicates success or failure. If the statement is successfully prepared, the next step is to execute it by invoking the %Execute() method.
set tResult = tStatement.%Execute()
The %Execute() method returns an instance of the %SQL.StatementResult class. Refer to that class for more information on the result object interface. All result objects support a %Display() method that is useful for testing.
The following example demonstrates the use of the %Prepare(), %Execute, and %Display() methods:
SAMPLES>s tStatus = tStatement.%Prepare(.tSQL) SAMPLES>w tStatus 1 SAMPLES>s tResult = tStatement.%Execute() SAMPLES>d tResult.%Display() id Name DOB Home_State 99 Finn,George V. 03/23/1928 MA 140 Hanson,James K. 04/02/1928 VT 14 Klein,Michael X. 06/17/1923 WV 159 Klingman,Brenda U. 07/09/1924 WA 49 Paladino,Rhonda H. 06/29/1923 AR 63 Vonnegut,Nellie K. 03/24/1926 HI 146 Zimmerman,Martin K. 05/25/1924 OH 7 Rows(s) Affected
Once an SQL statement has been successfully prepared, its %Metadata property is available. %Metadata is an instance of the %SQL.StatementMetadata class. %SQL.Metadata implements a %Display() method that is useful for examining the metadata interactively, such as:
SAMPLES>do tStatement.%Metadata.%Display()
Columns (property 'columns'):
Column Name Type Prec Scale Null
----------- ---- ---- ----- ----
id 4 10 0 0 id Person Sample 0 Y N N Y0 1
Name 12 50 0 0 Name Person Sample 0 N N N N0 0
DOB 9 10 0 1 DOB Person Sample 0 N N N N0 0
Home_State 12 2 0 1 Home_State Person Sample 0 N N N N0 0
Statement Parameters (property 'parameters'):
Nbr. Type precision scale nullable colName columntype
---- ---- --------- ----- -------- ------------ ----------
1 4 10 0 1 %parm(1) 1
2 12 2 0 1 %parm(2) 1
Formal Parameters (property 'formalParameters'):
Nbr. Type precision scale nullable colName columntype
---- ---- --------- ----- -------- ------------ ----------
2 4 10 0 1 %parm(1) 1
2 12 2 0 1 %parm(2) 1
Objects:
Column Name Extent ExportCall
----------- ------ ----------
%%ID Sample.Person %QuickLoad^Sample.Person.T1(%rowid,%nolock,0,0,1)
SAMPLES>
You can execute a successfully prepared statement repeatedly. This is most useful when the statement includes parameters, where a parameter is defined in the SQL statement source by a question mark (“?”). A statement may include an arbitrary number of parameters. (There are system limitations that limit the number of dynamic parameters; up to 200 are always supported.)
The %Execute() method accepts parameter values in the order in which they appear in the source statement. For example:
SAMPLES>set tSQL=3 SAMPLES>set tSQL(1)="select %ID as id,Name,DOB,Home_State" SAMPLES>set tSQL(2)="from Person where Age > ? and Home_State = ?" SAMPLES>set tSQL(3)="order by 2" SAMPLES>set tStatus = tStatement.%Prepare(.tSQL) SAMPLES>set tResult = tStatement.%Execute(80,"VT") SAMPLES>do tResult.%Display() id Name DOB Home_State 140 Hanson,James K. 04/02/1928 VT 1 Rows(s) Affected SAMPLES>set tResult = tStatement.%Execute(50,"VT") SAMPLES>do tResult.%Display() id Name DOB Home_State 3 Eagleman,Emilio N. 09/01/1946 VT 140 Hanson,James K. 04/02/1928 VT 167 Hertz,Keith O. 01/01/1952 VT 3 Rows(s) Affected SAMPLES>
You can also use the same statement object for many different statements by simply invoking %Prepare() with the new statement. This is because %Prepare() initializes the statement’s execution plan and metadata. Also, an arbitrary number of statement objects can coexist in the same process.
You can also prepare and execute dynamic SQL statements by calling %ExecDirect(). This method prepares the statement and, if it prepares the statement successfully, executes it with the supplied argument values. An optional by-reference parameter returns an instance of %SQL.Statement; this instance contains the currently prepared statement. You can then execute that statement instance just as if it had been instantiated by invoking %New() followed by a call to %Prepare(). You can also use that statement instance to prepare other dynamic statements just as if it were instantiated by %New().
If an error occurs during either statement preparation or execution, then the error is described in the result object properties of %SQLCODE and %Message. Always check the result property %SQLCODE for an error following %Execute() and %ExecDirect().
SAMPLES>set tResult = ##class(%SQL.Statement).%ExecDirect(.tStatement,"select name,age from Sample.Person where age > ? and home_state = ?",50,"VT") SAMPLES>write tResult.%SQLCODE 0 SAMPLES>do tResult.%Display() Name Age Eagleman,Emilio N. 62 Hanson,James K. 81 Hertz,Keith O. 57 3 Rows(s) Affected SAMPLES>write tStatement 1@%SQL.Statement SAMPLES>set tResult = tStatement.%Execute(40,"AK") SAMPLES>do tResult.%Display() Name Age Finn,Quentin O. 66 1 Rows(s) Affected SAMPLES>
Property Inventory
Method Inventory
- %ClassPath()
- %DialectSet()
- %Display()
- %ExecDirect()
- %ExecDirectNoPriv()
- %Execute()
- %GetImplementationDetails()
- %Prepare()
- %PrepareClassQuery()
- %PreparedStatementSet()
- execute()
- preparse()
Properties
- If %ObjectSelectMode is false (the default), then the property corresponding to the swizzleable column will be defined in result sets as a simple literal type corresponding to the SQL table's ROWID type.
- If %ObjectSelectMode is true, then the property will be defined with the column's declared type. That means that accessing the result set property will trigger swizzling.
%SchemaPath provides a list of schema names for resolving unqualified names during statement preparation. By default, its value is null; to set its value, use a comma-delimited list of schema names:
Set %SQL.Statement.%SchemaPath = "My_Schema,Your_Schema,DEFAULT_SCHEMA"
This is equivalent to the macro-preprocessor directive for embedded SQL:
#sqlcompile PATH = My_Schema,Your_Schema,DEFAULT_SCHEMA
PATH is a search path: if the unqualified name is found in a schema in the PATH, then this schema is used to qualify the name and no further searching is performed.
You can set the value of %SchemaPath at any time, but it is only used by the %Prepare method.
%SchemaPath can contain special schema name tokens that are resolved by the SQL compiler. Special tokens are:
- CURRENT_SCHEMA is the current default schema. If the %SQL.Statement call is defined in a class method, CURRENT_SCHEMA is the schema mapped to the current class package. If the statement is defined in a .MAC routine, CURRENT_SCHEMA is the configuration default schema.
- CURRENT_PATH is the currently defined schema search path. You can use this to add an additional schema to the search path while retaining the current search path.
- DEFAULT_SCHEMA specifies the use of the system-defined default schema.
You can also set %SchemaPath to a PATH value that is constructed from a given class definition; simply set %SchemaPath to ##class(%SQL.Statement).%ClassPath(classname).
Possible values are:
- 0 for LOGICAL mode.
- 1 for ODBC mode.
- 2 for DISPLAY mode.
Methods
- pHStatement - OPTIONAL (byref) the statement handle. If an actual arg is passed by reference then it will be populated with an OREF to a new statement object.
- pStatementText - (byref) SQL statement text. This can be an array of SQL statement lines with the base node set to the number of lines or - it can be a single string.
- %parm... - variable number of arguments that represent the values to be bound to parameters contained in pStatementText.
Only parameters with input direction (input or input-output) are actually used but a position for each '?' contained in
pStatementText needs to be represented. In the statement:
? = call Sample.PersonSets(?,?)
The %parms... list must contain an empty position for the return value. An example of a call to %ExecDirect for such a statement is:In this example, the return value is allocated a position in the %parms list (the ,,), "A" is bound to the first argument passed to Sample.PersonSets and "NY" is bound to the second.set tRes = ##class(%SQL.Statement).%ExecDirect(.tStmt,"?=call Sample.PersonSets(?,?)",,"A","NY")
Executes the current statement and returns the result as an instance of %SQL.StatementResult. The result of the execute is always the return value. Success/Failure information is reported in the result object as %SQLCODE, %Message, %ROWCOUNT, and/or %ROWID.
The %Execute() method accepts parameter values in the order in which they appear in the source statement. For example:
SAMPLES>set tSQL=3 SAMPLES>set tSQL(1)="select %ID as id,Name,DOB,Home_State" SAMPLES>set tSQL(2)="from Person where Age > ? and Home_State = ?" SAMPLES>set tSQL(3)="order by 2" SAMPLES>set tStatus = tStatement.%Prepare(.tSQL) SAMPLES>set tResult = tStatement.%Execute(80,"VT") SAMPLES>do tResult.%Display() id Name DOB Home_State 140 Hanson,James K. 04/02/1928 VT 1 Rows(s) Affected SAMPLES>set tResult = tStatement.%Execute(50,"VT") SAMPLES>do tResult.%Display() id Name DOB Home_State 3 Eagleman,Emilio N. 09/01/1946 VT 140 Hanson,James K. 04/02/1928 VT 167 Hertz,Keith O. 01/01/1952 VT 3 Rows(s) Affected SAMPLES>
You can also use the same statement object for many different statements by simply invoking %Prepare() with the new statement. This is because %Prepare() initializes the statement’s execution plan and metadata. Also, an arbitrary number of statement objects can coexist in the same process.
The %parm... input parameter represents a variable number of arguments that represent the values to be bound to parameters contained in pStatementText. Only parameters with input direction (input or input-output) are actually used but the position of each '?' contained in the source statement must be maintained.
An example of calling %Execute for a prepared statement "? = call Sample.PersonSets(?,?)" is:
set tStatement = ##class(%SQL.Statement).%New()
set tStatus = tStatement.%Prepare("?=call Sample.PersonSets(?,?)")
set tResult = tStatement.%Execute(,"A","NY")
Returns the details of the currently prepared statement. This method returns the implementation class, the statement text, and the actual arguments bound to formal statement arguments.
- pClassName contains the name of the current statement's implementation class.
- pStatementText contains the statement text. This variable is either a simple string or an array of strings where pStatementText is the number of lines and pStatementText(line) is a line of statement text.
- pArguments is a $list containing argument types and argument value in the form $list(arg1type, arg1value[, arg2type, arg2value...argNtype, argNvalue]). There are three argument types: 'c' = constant, 'v' = host variable and '?' is a parameter. All three argument types are replaced by ? arguments during statement prepare to improve the efficiency of the statement cache. Only actual arguments of type '?' require a value to be supplied when executing the statement.
- pStatementType is an integer value corresponding to the internal type number for the type of statement. This type number is for internal use and subject to change.
This method returns 1 for success and 0 for failure. This method fails when no statement has been prepared.
The checkPriv argument can be used to not perform SQL privilege checking on the statement if checkPriv=0. The default is that privileges will be checked.
set status = stmt.%PrepareClassQuery("%Library.File","FileSet")
All parameters defined in the formal specification of the query are assigned placeholder '?' in the generated CALL statement. Actual values for those parameters can be passed in the %Execute() call. %Metadata is available after a successful prepare.
Because this method generates a CALL statement, the executed class query must have the SqlProc keyword set to True. Class queries defined with SqlProc = False cannot be called by %PrepareClassQuery.
The checkPriv argument can be used to not perform SQL EXECUTE privilege checking on the class queryes procedure call if checkPriv=0. The default is that privileges will be checked.
Inherited Members
Inherited Methods
- %AddToSaveSet()
- %ClassIsLatestVersion()
- %ClassName()
- %ConstructClone()
- %DispatchClassMethod()
- %DispatchGetModified()
- %DispatchGetProperty()
- %DispatchMethod()
- %DispatchSetModified()
- %DispatchSetMultidimProperty()
- %DispatchSetProperty()
- %Extends()
- %GetParameter()
- %IsA()
- %IsModified()
- %New()
- %NormalizeObject()
- %ObjectModified()
- %OriginalNamespace()
- %PackageName()
- %RemoveFromSaveSet()
- %SerializeObject()
- %SetModified()
- %ValidateObject()