7. Using Bind Variables — python-oracledb 3.2.0b1 documentation (original) (raw)

SQL and PL/SQL statements that pass data to and from Oracle Database should use placeholders in SQL and PL/SQL statements that mark where data is supplied or returned. A bind variable placeholder is a colon-prefixed identifier or numeral. For example, :dept_id and :dept_name are the two bind variable placeholders in this SQL statement:

sql = """insert into departments (department_id, department_name) values (:dept_id, :dept_name)""" cursor.execute(sql, [280, "Facility"])

As part of execution, the supplied bind variable values 280 and"Facility" are substituted for the placeholders by the database. This is called binding.

Using bind variables is important for scalability and security. They help avoid SQL Injection security problems because data is never treated as part of an executable statement when it is parsed.

Bind variables reduce parsing and execution costs when statements are executed more than once with different data values. If you do not use bind variables, Oracle must reparse and cache multiple statements. When using bind variables, Oracle Database may be able to reuse the statement execution plan and context.

Warning

Never concatenate or interpolate user data into SQL statements:

did = 280 dnm = "Facility"

!! Never do this !!

sql = f"""insert into departments (department_id, department_name) values ({did}, '{dnm}')""" cursor.execute(sql)

This is a security risk and can impact performance and scalability.

Bind variables can be used to substitute data, but cannot be used to substitute the text of the statement. You cannot, for example, use a bind variable placeholder where a column name or a table name is required. Bind variable placeholders also cannot be used in Data Definition Language (DDL) statements, such as CREATE TABLE or ALTER statements.

7.1. Binding by Name or Position

Binding can be done “by name” or “by position”.

7.1.1. Bind by Name

A named bind is performed when the bind variables in the Python statement use the names of placeholders in the SQL or PL/SQL statement. For example:

cursor.execute(""" insert into departments (department_id, department_name) values (:dept_id, :dept_name)""", dept_id=280, dept_name="Facility")

Alternatively, the parameters can be passed as a dictionary instead of as keyword parameters:

data = dict(dept_id=280, dept_name="Facility") cursor.execute(""" insert into departments (department_id, department_name) values (:dept_id, :dept_name)""", data)

In the above examples, the keyword parameter names or the keys of the dictionary must match the bind variable placeholder names.

The advantages of named binding are that the order of the bind values in theexecute() parameter is not important, the names can be meaningful, and the placeholder names can be repeated while still only supplying the value once in the application.

An example of reusing a bind variable placeholder is:

cursor.execute(""" update departments set department_id = :dept_id + 10 where department_id = :dept_id""", dept_id=280)

7.1.2. Bind by Position

Positional binding occurs when a list or tuple of bind values is passed to theexecute() call. For example:

cursor.execute(""" insert into departments (department_id, department_name) values (:1, :2)""", [280, "Facility"])

The following example (which changes the order of the bind placeholder names) has exactly the same behavior. The value used to substitute the placeholder “:2” will be the first element of the list and “:1” will be replaced by the second element. Bind by position works from left to right and pays no attention to the name of the bind variable:

cursor.execute(""" insert into departments (department_id, department_name) values (:2, :1)""", [280, "Facility"])

The following example is also bind by position despite the bind placeholders having alphabetic names. The actual process of binding uses the list positions of the input data to associate the data with the placeholder locations:

cursor.execute(""" insert into departments (department_id, department_name) values (:dept_id, :dept_name)""", [280, "Facility"])

Python tuples can also be used for binding by position:

cursor.execute(""" insert into departments (department_id, department_name) values (:1, :2)""", (280, "Facility"))

If only a single bind placeholder is used in the SQL or PL/SQL statement, the data can be a list like [280] or a single element tuple like (280,).

When using bind by position for SQL statements, the order of the bind values must exactly match the order of each bind variable and duplicated names must have their values repeated. For PL/SQL statements, however, the order of the bind values must exactly match the order of each unique bind variable found in the PL/SQL block and values should not be repeated. In order to avoid this difference, binding by name is recommended when bind variable names are repeated.

7.2. Bind Direction

The caller can supply data to the database (IN), the database can return data to the caller (OUT) or the caller can supply initial data to the database and the database can supply the modified data back to the caller (IN/OUT). This is known as the bind direction.

The examples shown above have all supplied data to the database and are therefore classified as IN bind variables. In order to have the database return data to the caller, a variable must be created. This is done by calling the method Cursor.var(), which identifies the type of data that will be found in that bind variable and its maximum size among other things.

Here is an example showing how to use OUT binds. It calculates the sum of the integers 8 and 7 and stores the result in an OUT bind variable of type integer:

out_val = cursor.var(int) cursor.execute(""" begin :out_val := :in_bind_var1 + :in_bind_var2; end;""", out_val=out_val, in_bind_var1=8, in_bind_var2=7) print(out_val.getvalue()) # will print 15

If instead of simply getting data back you wish to supply an initial value to the database, you can set the variable’s initial value. This example is the same as the previous one but it sets the initial value first:

in_out_var = cursor.var(int) in_out_var.setvalue(0, 25) cursor.execute(""" begin :in_out_bind_var := :in_out_bind_var + :in_bind_var1 + :in_bind_var2; end;""", in_out_bind_var=in_out_var, in_bind_var1=8, in_bind_var2=7) print(in_out_var.getvalue()) # will print 40

When binding data to parameters of PL/SQL procedures that are declared as OUT parameters, it is worth noting that any value that is set in the bind variable will be ignored. In addition, any parameters declared as IN/OUT that do not have a value set will start out with a value of null.

7.3. Binding Null Values

To insert a NULL into a character column you can bind the Python singletonNone. For example, with the table:

create table tab (id number, val varchar2(50));

You can use:

cursor.execute("insert into tab (id, val) values (:i, :v)", i=280, v=None)

Python-oracledb assumes the value will be a string (equivalent to a VARCHAR2 column). If you need to use a different Oracle Database data type you will need to make a call to Cursor.setinputsizes() or create a bind variable with the correct type by calling Cursor.var().

For example, if the table had been created using an Oracle Spatial SDO_GEOMETRY object column:

create table tab (id number, val sdo_geometry);

Then the previous code would fail with:

ORA-00932: expression is of data type CHAR, which is incompatible with expected data type MDSYS.SDO_GEOMETRY

To insert a NULL into the new table, use:

type_obj = connection.gettype("SDO_GEOMETRY") var = cursor.var(type_obj) cursor.execute("insert into tab (id, val) values (:i, :v)", i=280, v=var)

Alternatively use:

type_obj = connection.gettype("SDO_GEOMETRY") cursor.setinputsizes(i=None, v=type_obj) cursor.execute("insert into tab (id, val) values (:i, :v)", i=280, v=None)

7.4. Binding ROWID Values

The pseudo-column ROWID uniquely identifies a row in a table. In python-oracledb, ROWID values are represented as strings. The example below shows fetching a row and then updating that row by binding its rowid:

fetch the row

cursor.execute(""" select rowid, manager_id from departments where department_id = :dept_id""", dept_id=280) rowid, manager_id = cursor.fetchone()

update the row by binding ROWID

cursor.execute(""" update departments set manager_id = :manager_id where rowid = :rid""", manager_id=205, rid=rowid)

7.5. Binding UROWID Values

Universal rowids (UROWID) are used to uniquely identify rows in index organized tables. In python-oracledb, UROWID values are represented as strings. The example below shows fetching a row from index organized tableuniversal_rowids and then updating that row by binding its urowid:

CREATE TABLE universal_rowids ( int_col number(9) not null, str_col varchar2(250) not null, date_col date not null, CONSTRAINT universal_rowids_pk PRIMARY KEY(int_col, str_col, date_col) ) ORGANIZATION INDEX

ridvar = cursor.var(oracledb.DB_TYPE_UROWID)

fetch the row

cursor.execute(""" begin select rowid into :rid from universal_rowids where int_col = 3; end;""", rid=ridvar)

update the row by binding UROWID

cursor.execute(""" update universal_rowids set str_col = :str_val where rowid = :rowid_val""", str_val="String #33", rowid_val=ridvar)

Note that the type oracledb.DB_TYPE_UROWID is only supported in python-oracledb Thin mode. For python-oracledb Thick mode, the database type UROWID can be bound with type oracledb.DB_TYPE_ROWID. See Query Metadata in Thin and Thick Modes.

7.6. DML RETURNING Bind Variables

When a RETURNING clause is used with a DML statement like UPDATE, INSERT, or DELETE, the values are returned to the application through the use of OUT bind variables. Consider the following example:

The RETURNING INTO bind variable is a string

dept_name = cursor.var(str)

cursor.execute(""" update departments set location_id = :loc_id where department_id = :dept_id returning department_name into :dept_name""", loc_id=1700, dept_id=50, dept_name=dept_name) print(dept_name.getvalue()) # will print ['Shipping']

In the above example, since the WHERE clause matches only one row, the output contains a single item in the list. If the WHERE clause matched multiple rows, the output would contain as many items as there were rows that were updated.

The same bind variable placeholder name cannot be used both before and after the RETURNING clause. For example, if the :dept_name bind variable is used both before and after the RETURNING clause:

a variable cannot be used for both input and output in a DML returning

statement

dept_name_var = cursor.var(str) dept_name_var.setvalue(0, 'Input Department') cursor.execute(""" update departments set department_name = :dept_name || ' EXTRA TEXT' returning department_name into :dept_name""", dept_name=dept_name_var)

The above example will not update the bind variable as expected, but no error will be raised if you are using python-oracledb Thick mode. With python-oracledb Thin mode, the above example returns the following error:

DPY-2048: the bind variable placeholder ":dept_name" cannot be used both before and after the RETURNING clause in a DML RETURNING statement

7.7. LOB Bind Variables

Database CLOBs, NCLOBS, BLOBs, and BFILEs can be bound with typesoracledb.DB_TYPE_CLOB, oracledb.DB_TYPE_NCLOB,oracledb.DB_TYPE_BLOB and oracledb.DB_TYPE_BFILErespectively. LOBs fetched from the database or created withConnection.createlob() can also be bound.

LOBs may represent Oracle Database persistent LOBs (those stored in tables) or temporary LOBs (such as those created with Connection.createlob() or returned by some SQL and PL/SQL operations).

LOBs can be used as IN, OUT, or IN/OUT bind variables.

See Using CLOB, BLOB, NCLOB, and BFILE Data for examples.

7.8. REF CURSOR Bind Variables

Python-oracledb provides the ability to bind and define PL/SQL REF cursors. As an example, consider the PL/SQL procedure:

CREATE OR REPLACE PROCEDURE find_employees ( p_query IN VARCHAR2, p_results OUT SYS_REFCURSOR ) AS BEGIN OPEN p_results FOR SELECT employee_id, first_name, last_name FROM employees WHERE UPPER(first_name || ' ' || last_name || ' ' || email) LIKE '%' || UPPER(p_query) || '%'; END; /

A newly opened cursor can be bound to the REF CURSOR parameter as shown in the following Python code. After the PL/SQL procedure has been called withCursor.callproc(), the cursor can then be fetched just like any other cursor which had executed a SQL query:

ref_cursor = connection.cursor() cursor.callproc("find_employees", ['Smith', ref_cursor]) for row in ref_cursor: print(row)

With Oracle’s sample HR schema there are two employees with the last name ‘Smith’ so the result is:

(159, 'Lindsey', 'Smith') (171, 'William', 'Smith')

To return a REF CURSOR from a PL/SQL function, use oracledb.DB_TYPE_CURSOR for the return type of Cursor.callfunc():

ref_cursor = cursor.callfunc('example_package.f_get_cursor', oracledb.DB_TYPE_CURSOR) for row in ref_cursor: print(row)

See Tuning python-oracledb for information on how to tune REF CURSORS.

Also see Implicit Results which provides an alternative way to return query results from PL/SQL procedures.

7.9. Binding PL/SQL Collections

PL/SQL Collections like Associative Arrays can be bound as IN, OUT, and IN/OUT variables. When binding IN values, an array can be passed directly as shown in this example, which sums up the lengths of all of the strings in the provided array. First the PL/SQL package definition:

create or replace package mypkg as

type udt_StringList is table of varchar2(100) index by binary_integer;

function DemoCollectionIn (
    a_Values            udt_StringList
) return number;

end; /

create or replace package body mypkg as

function DemoCollectionIn (
    a_Values            udt_StringList
) return number is
    t_ReturnValue       number := 0;
begin
    for i in 1..a_Values.count loop
        t_ReturnValue := t_ReturnValue + length(a_Values(i));
    end loop;
    return t_ReturnValue;
end;

end; /

Then the Python code:

values = ["String One", "String Two", "String Three"] return_val = cursor.callfunc("mypkg.DemoCollectionIn", int, [values]) print(return_val) # will print 32

In order get values back from the database, a bind variable must be created using Cursor.arrayvar(). The first parameter to this method is a Python type that python-oracledb knows how to handle or one of the oracledb DB API Types. The second parameter is the maximum number of elements that the array can hold or an array providing the value (and indirectly the maximum length). The final parameter is optional and only used for strings and bytes. It identifies the maximum length of the strings and bytes that can be stored in the array. If not specified, the length defaults to 4000 bytes.

Consider the following PL/SQL package:

create or replace package mypkg as

type udt_StringList is table of varchar2(100) index by binary_integer;

procedure DemoCollectionOut (
    a_NumElements       number,
    a_Values            out nocopy udt_StringList
);

procedure DemoCollectionInOut (
    a_Values            in out nocopy udt_StringList
);

end; /

create or replace package body mypkg as

procedure DemoCollectionOut (
    a_NumElements       number,
    a_Values            out nocopy udt_StringList
) is
begin
    for i in 1..a_NumElements loop
        a_Values(i) := 'Demo out element #' || to_char(i);
    end loop;
end;

procedure DemoCollectionInOut (
    a_Values            in out nocopy udt_StringList
) is
begin
    for i in 1..a_Values.count loop
        a_Values(i) := 'Converted element #' || to_char(i) ||
                ' originally had length ' || length(a_Values(i));
    end loop;
end;

end; /

The Python code to process an OUT collection will be as follows. Note the call to Cursor.arrayvar() which creates space for an array of strings. Each string permits up to 100 bytes and only 10 strings are permitted. If the PL/SQL block exceeds the maximum number of strings allowed the errorORA-06513: PL/SQL: index for PL/SQL table out of range for host language array will be raised.

out_array_var = cursor.arrayvar(str, 10, 100) cursor.callproc("mypkg.DemoCollectionOut", [5, out_array_var]) for val in out_array_var.getvalue(): print(val)

This would produce the following output:

Demo out element #1 Demo out element #2 Demo out element #3 Demo out element #4 Demo out element #5

The Python code to process IN/OUT collections is similar. Note the different call to Cursor.arrayvar() which creates space for an array of strings, but uses an array to determine both the maximum length of the array and its initial value.

in_values = ["String One", "String Two", "String Three", "String Four"] in_out_array_var = cursor.arrayvar(str, in_values) cursor.callproc("mypkg.DemoCollectionInOut", [in_out_array_var]) for val in in_out_array_var.getvalue(): print(val)

This will produce the following output:

Converted element #1 originally had length 10 Converted element #2 originally had length 10 Converted element #3 originally had length 12 Converted element #4 originally had length 11

If an array variable needs to have an initial value but also needs to allow for more elements than the initial value contains, the following code can be used instead:

in_out_array_var = cursor.arrayvar(str, 10, 100) in_out_array_var.setvalue(0, ["String One", "String Two"])

All of the collections that have been bound in preceding examples have used contiguous array elements. If an associative array with sparse array elements is needed, a different approach is required. Consider the following PL/SQL code:

create or replace package mypkg as

type udt_StringList is table of varchar2(100) index by binary_integer;

procedure DemoCollectionOut (
    a_Value                         out nocopy udt_StringList
);

end; /

create or replace package body mypkg as

procedure DemoCollectionOut (
    a_Value                         out nocopy udt_StringList
) is
begin
    a_Value(-1048576) := 'First element';
    a_Value(-576) := 'Second element';
    a_Value(284) := 'Third element';
    a_Value(8388608) := 'Fourth element';
end;

end; /

Note that the collection element indices are separated by large values. The technique used above would fail with the exception ORA-06513: PL/SQL: index for PL/SQL table out of range for host language array. The code required to process this collection looks like this instead:

collection_type = connection.gettype("MYPKG.UDT_STRINGLIST") collection = collection_type.newobject() cursor.callproc("mypkg.DemoCollectionOut", [collection]) print(collection.aslist())

This produces the output:

['First element', 'Second element', 'Third element', 'Fourth element']

Note the use of Object.aslist() which returns the collection element values in index order as a simple Python list. The indices themselves are lost in this approach. The associative array can be turned into a Python dictionary using Object.asdict(). If that value was printed in the previous example instead, the output would be:

{-1048576: 'First element', -576: 'Second element', 284: 'Third element', 8388608: 'Fourth element'}

If the elements need to be traversed in index order, the methodsObject.first() and Object.next() can be used. The methodObject.getelement() can be used to acquire the element at a particular index. This is shown in the following code:

ix = collection.first() while ix is not None: print(ix, "->", collection.getelement(ix)) ix = collection.next(ix)

This produces the output:

-1048576 -> First element -576 -> Second element 284 -> Third element 8388608 -> Fourth element

Similarly, the elements can be traversed in reverse index order using the methods Object.last() and Object.prev() as shown in the following code:

ix = collection.last() while ix is not None: print(ix, "->", collection.getelement(ix)) ix = collection.prev(ix)

This produces the output:

8388608 -> Fourth element 284 -> Third element -576 -> Second element -1048576 -> First element

7.10. Binding PL/SQL Records

PL/SQL record type objects can also be bound for IN, OUT, and IN/OUT bind variables. For example:

create or replace package mypkg as

type udt_DemoRecord is record (
    NumberValue                     number,
    StringValue                     varchar2(30),
    DateValue                       date,
    BooleanValue                    boolean
);

procedure DemoRecordsInOut (
    a_Value                         in out nocopy udt_DemoRecord
);

end; /

create or replace package body mypkg as

procedure DemoRecordsInOut (
    a_Value                         in out nocopy udt_DemoRecord
) is
begin
    a_Value.NumberValue := a_Value.NumberValue * 2;
    a_Value.StringValue := a_Value.StringValue || ' (Modified)';
    a_Value.DateValue := a_Value.DateValue + 5;
    a_Value.BooleanValue := not a_Value.BooleanValue;
end;

end; /

Then this Python code can be used to call the stored procedure which will update the record:

create and populate a record

record_type = connection.gettype("MYPKG.UDT_DEMORECORD") record = record_type.newobject() record.NUMBERVALUE = 6 record.STRINGVALUE = "Test String" record.DATEVALUE = datetime.datetime(2016, 5, 28) record.BOOLEANVALUE = False

show the original values

print("NUMBERVALUE ->", record.NUMBERVALUE) print("STRINGVALUE ->", record.STRINGVALUE) print("DATEVALUE ->", record.DATEVALUE) print("BOOLEANVALUE ->", record.BOOLEANVALUE) print()

call the stored procedure which will modify the record

cursor.callproc("mypkg.DemoRecordsInOut", [record])

show the modified values

print("NUMBERVALUE ->", record.NUMBERVALUE) print("STRINGVALUE ->", record.STRINGVALUE) print("DATEVALUE ->", record.DATEVALUE) print("BOOLEANVALUE ->", record.BOOLEANVALUE)

This will produce the following output:

NUMBERVALUE -> 6 STRINGVALUE -> Test String DATEVALUE -> 2016-05-28 00:00:00 BOOLEANVALUE -> False

NUMBERVALUE -> 12 STRINGVALUE -> Test String (Modified) DATEVALUE -> 2016-06-02 00:00:00 BOOLEANVALUE -> True

Note that when manipulating records, all of the attributes must be set by the Python program in order to avoid an Oracle Client bug which will result in unexpected values or the Python application segfaulting.

7.11. Binding Spatial Data Types

Oracle Spatial data types objects can be represented by Python objects and their attribute values can be read and updated. The objects can further be bound and committed to database. This is similar to the examples above.

An example of fetching SDO_GEOMETRY is in Oracle Database Objects and Collections.

7.12. Reducing the SQL Version Count

When repeated calls to Cursor.execute() or Cursor.executemany()bind different string data lengths, then using Cursor.setinputsizes()can help reduce Oracle Database’s SQL “version count” for the statement. The version count is the number of child cursors used for the same statement text. The database will have a parent cursor representing the text of a statement, and a number of child cursors for differing executions of the statement, for example when different bind variable types or lengths are used.

For example, with a table created as:

create table mytab (c1 varchar2(25), c2 varchar2(100), c3 number);

You can use setinputsizes() to help reduce the number of child cursors:

sql = "insert into mytab (c1, c2) values (:1, :2)"

cursor.setinputsizes(25, 15)

s1 = "abc" s2 = "def" cursor.execute(sql, [s1, s2])

s1 = "aaaaaaaaaaaaaaaaaaaaaaaaa" s2 = "z" cursor.execute(sql, [s1, s2])

The setinputsizes() call indicates that the first value bound will be a Python string of no more than 25 characters and the second value bound will be a string of no more than 15 characters. If the data string lengths exceed the setinputsizes() values, then python-oracledb will accept them but there will be no processing benefit.

It is not uncommon for SQL statements to have low hundreds of versions. Sometimes this is expected and not a result of any issue. To determine the reason, find the SQL identifier of the statement and then query the Oracle Database view V$SQL_SHARED_CURSOR.

The SQL identifier of a statement can be found in Oracle Database views likeV$SQLAREA after you have run a statement, or you can find it_before_ you execute the statement by using the DBMS_SQL_TRANSLATOR.SQL_ID() function. Make sure to pass in exactly the same SQL text, including the same whitespace:

sql = "insert into mytab (c1, c2) values (:1, :2)" # statement to examine

cursor.execute("select dbms_sql_translator.sql_id(:1) from dual", [sql]) (sqlid,) = cursor.fetchone(); print(sqlid)

This might print a value like:

Then, to find the SQL versions, run a query to see the child cursors. For example:

cursor.execute("""select child_number, reason from v$sql_shared_cursor where sql_id = :1 order by 1""", [sqlid]) col_names = [c.name for c in cursor.description] for row in cursor.fetchall(): r = [dict(zip(col_names, row))] print(r)

With the earlier code that used setinputsizes() and inserted different data lengths you might see:

[{'CHILD_NUMBER': 0, 'REASON': ' '}]

However if setinputsizes() had not been used, you would see two rows and REASON would include the text “Bind mismatch”, for example:

[{'CHILD_NUMBER': 0, 'REASON': '039Bind mismatch(22)4x80132128 '}] [{'CHILD_NUMBER': 1, 'REASON': '139Bind mismatch(22)4x80112832 '}]

7.13. Changing Bind Data Types using an Input Type Handler

Input Type Handlers allow applications to change how data is bound to statements, or even to enable new types to be bound directly.

An input type handler is enabled by setting the attributeCursor.inputtypehandler or Connection.inputtypehandler.

Inserting NaN values as NULL in NUMBER columns

To insert NaN values as NULLs in a NUMBER column, use an input type handler with an inconverter:

def input_type_handler(cursor, value, arraysize): if isinstance(value, float): return cursor.var(oracledb.DB_TYPE_NUMBER, arraysize=arraysize, inconverter=lambda x: None if math.isnan(x) else x)

connection.inputtypehandler = input_type_handler

Note that this is not needed for BINARY_FLOAT or BINARY_DOUBLE columns.

Binding Python Objects

Input type handlers can be combined with variable converters to bind Python objects seamlessly:

A standard Python object

class Building:

def __init__(self, build_id, description, num_floors, date_built):
    self.building_id = build_id
    self.description = description
    self.num_floors = num_floors
    self.date_built = date_built

building = Building(1, "Skyscraper 1", 5, datetime.date(2001, 5, 24))

Get Python representation of the Oracle user defined type UDT_BUILDING

obj_type = con.gettype("UDT_BUILDING")

convert a Python Building object to the Oracle user defined type

UDT_BUILDING

def building_in_converter(value): obj = obj_type.newobject() obj.BUILDINGID = value.building_id obj.DESCRIPTION = value.description obj.NUMFLOORS = value.num_floors obj.DATEBUILT = value.date_built return obj

def input_type_handler(cursor, value, num_elements): if isinstance(value, Building): return cursor.var(obj_type, arraysize=num_elements, inconverter=building_in_converter)

With the input type handler, the bound Python object is converted

to the required Oracle object before being inserted

cur.inputtypehandler = input_type_handler cur.execute("insert into myTable values (:1, :2)", (1, building))

7.14. Binding Multiple Values to a SQL WHERE IN Clause

To use a SQL IN list with multiple values, use one bind variable placeholder per value. You cannot directly bind a Python list or dictionary to a single bind variable. For example, to use two values in an IN clause your code should be like:

items = ["Smith", "Taylor"] cursor.execute(""" select employee_id, first_name, last_name from employees where last_name in (:1, :2)""", items) for row in cursor: print(row)

This gives the output:

(159, 'Lindsey', 'Smith') (171, 'William', 'Smith') (176, 'Jonathon', 'Taylor') (180, 'Winston', 'Taylor')

If the query is executed multiple times with differing numbers of values, a bind variable placeholder should be included in the SQL statement for each of the maximum possible number of values. If the statement is executed with a lesser number of data values, then bind None for missing values. For example, if a query is used for up to five values, but only two values are used in a particular execution, the code could be:

items = ["Smith", "Taylor", None, None, None] cursor.execute(""" select employee_id, first_name, last_name from employees where last_name in (:1, :2, :3, :4, :5)""", items) for row in cursor: print(row)

This will produce the same output as the original example.

Reusing the same SQL statement like this for a variable number of values, instead of constructing a unique statement per set of values, allows best reuse of Oracle Database resources. Additionally, if a statement with a large number of bind variable placeholders is executed many times with varying string lengths for each execution, then consider using Cursor.setinputsizes()to reduce Oracle Database’s SQL “version count” for the statement. For example, if the columns are VARCHAR2(25), then add this before the Cursor.execute() call:

cursor.setinputsizes(25,25,25,25,25)

If other bind variables are required in the statement, adjust the bind variable placeholder numbers appropriately:

binds = [120] # employee id binds += ["Smith", "Taylor", None, None, None] # IN list cursor.execute(""" select employee_id, first_name, last_name from employees where employee_id > :1 and last_name in (:2, :3, :4, :5, :6)""", binds) for row in cursor: print(row)

If a statement containing WHERE IN is not going to be re-executed, or the number of values is only going to be known at runtime, then a SQL statement can be dynamically built:

bind_values = ["Gates", "Marvin", "Fay"] bind_names = ",".join(":" + str(i + 1) for i in range(len(bind_values))) sql = f"select first_name, last_name from employees where last_name in ({bind_names})" cursor.execute(sql, bind_values) for row in cursor: print(row)

7.14.1. Binding a Large Number of Items in an IN List

The number of items in an IN list is limited to 65535 in Oracle Database 23ai, and to 1000 in earlier versions. If you exceed the limit, the database will return an error like ORA-01795: maximum number of expressions in a list is 65535.

To use more values in the IN clause list, you can add OR clauses like:

sql = """select . . . where key in (:0,:1,:2,:3,:4,:5,:6,:7,:8,:9,:10,:11,...) or key in (:50,:51,:52,:53,:54,:55,:56,:57,:58,:59,...) or key in (:100,:101,:102,:103,:104,:105,:106,:107,:108,:109,...)"""

A more general solution for a larger number of values is to construct a SQL statement like:

SELECT ... WHERE col IN ( )

The best way to do the ‘’ depends on how the data is initially represented and the number of items. For example you might look at using a global temporary table.

One method for large IN lists is to use an Oracle Database collection with theTABLE() clause. For example, if the following type was created:

SQL> CREATE OR REPLACE TYPE name_array AS TABLE OF VARCHAR2(25); 2 /

then the application could do:

type_obj = connection.gettype("NAME_ARRAY") obj = type_obj.newobject() obj.extend(["Smith", "Taylor"]) cursor.execute("""select employee_id, first_name, last_name from employees where last_name in (select * from table(:1))""", [obj]) for row in cursor: print(row)

When using this technique, it is important to review the database optimizer plan to ensure it is efficient.

Since this TABLE() solution uses an object type, there is a performance impact because of the extra round-trips required to get the type information. Unless you have a large number of binds you may prefer one of the previous solutions. For efficiency, retain the return value ofConnection.gettype() for reuse where possible instead of making repeated calls to it.

Some users employ the types SYS.ODCINUMBERLIST, SYS.ODCIVARCHAR2LIST, or SYS.ODCIDATELIST instead of creating their own type, but this should be used with the understanding that the database may remove these in a future version, and that their size is 32K - 1.

7.15. Binding Column and Table Names

Table names cannot be bound in SQL queries. You can concatenate text to build up a SQL statement, but ensure that you use an Allow List or other means to validate the data in order to avoid SQL Injection security issues:

table_allow_list = ['employees', 'departments'] table_name = get_table_name() # get the table name from user input if table_name.lower() not in table_allow_list: raise Exception('Invalid table name') sql = f'select * from {table_name}'

Binding column names can be done either by using a similar method, or by using a CASE statement. The example below demonstrates binding a column name in an ORDER BY clause:

sql = """ select * from departments order by case :bindvar when 'DEPARTMENT_ID' then department_id else manager_id end"""

col_name = get_column_name() # Obtain a column name from the user cursor.execute(sql, [col_name])

Depending on the name provided by the user, the query results will be ordered either by the column DEPARTMENT_ID or the column MANAGER_ID.