Inserting Rows with Core¶
When using Core, a SQL INSERT statement is generated using the
insert()
function - this function generates a new instance of
Insert
which represents an INSERT statement in SQL, that adds
new data into a table.
ORM Readers - The way that rows are INSERTed into the database from an ORM
perspective makes use of object-centric APIs on the Session
object known as the
unit of work process,
and is fairly different from the Core-only approach described here.
The more ORM-focused sections later starting at Inserting Rows with the ORM
subsequent to the Expression Language sections introduce this.
The insert() SQL Expression Construct¶
A simple example of Insert
illustrating the target table
and the VALUES clause at once:
>>> from sqlalchemy import insert
>>> stmt = insert(user_table).values(name="spongebob", fullname="Spongebob Squarepants")
The above stmt
variable is an instance of Insert
. Most
SQL expressions can be stringified in place as a means to see the general
form of what’s being produced:
>>> print(stmt)
INSERT INTO user_account (name, fullname) VALUES (:name, :fullname)
The stringified form is created by producing a Compiled
form
of the object which includes a database-specific string SQL representation of
the statement; we can acquire this object directly using the
ClauseElement.compile()
method:
>>> compiled = stmt.compile()
Our Insert
construct is an example of a “parameterized”
construct, illustrated previously at Sending Parameters; to
view the name
and fullname
bound parameters, these are
available from the Compiled
construct as well:
>>> compiled.params
{'name': 'spongebob', 'fullname': 'Spongebob Squarepants'}
Executing the Statement¶
Invoking the statement we can INSERT a row into user_table
.
The INSERT SQL as well as the bundled parameters can be seen in the
SQL logging:
>>> with engine.connect() as conn:
... result = conn.execute(stmt)
... conn.commit()
BEGIN (implicit)
INSERT INTO user_account (name, fullname) VALUES (?, ?)
[...] ('spongebob', 'Spongebob Squarepants')
COMMIT
In its simple form above, the INSERT statement does not return any rows, and if
only a single row is inserted, it will usually include the ability to return
information about column-level default values that were generated during the
INSERT of that row, most commonly an integer primary key value. In the above
case the first row in a SQLite database will normally return 1
for the
first integer primary key value, which we can acquire using the
CursorResult.inserted_primary_key
accessor:
>>> result.inserted_primary_key
(1,)
Tip
CursorResult.inserted_primary_key
returns a tuple
because a primary key may contain multiple columns. This is known as
a composite primary key. The CursorResult.inserted_primary_key
is intended to always contain the complete primary key of the record just
inserted, not just a “cursor.lastrowid” kind of value, and is also intended
to be populated regardless of whether or not “autoincrement” were used, hence
to express a complete primary key it’s a tuple.
Changed in version 1.4.8: the tuple returned by
CursorResult.inserted_primary_key
is now a named tuple
fulfilled by returning it as a Row
object.
INSERT usually generates the “values” clause automatically¶
The example above made use of the Insert.values()
method to
explicitly create the VALUES clause of the SQL INSERT statement. This method
in fact has some variants that allow for special forms such as multiple rows in
one statement and insertion of SQL expressions. However the usual way that
Insert
is used is such that the VALUES clause is generated
automatically from the parameters passed to the
Connection.execute()
method; below we INSERT two more rows to
illustrate this:
>>> with engine.connect() as conn:
... result = conn.execute(
... insert(user_table),
... [
... {"name": "sandy", "fullname": "Sandy Cheeks"},
... {"name": "patrick", "fullname": "Patrick Star"},
... ],
... )
... conn.commit()
BEGIN (implicit)
INSERT INTO user_account (name, fullname) VALUES (?, ?)
[...] (('sandy', 'Sandy Cheeks'), ('patrick', 'Patrick Star'))
COMMIT
The execution above features “executemany” form first illustrated at
Sending Multiple Parameters, however unlike when using the
text()
construct, we didn’t have to spell out any SQL.
By passing a dictionary or list of dictionaries to the Connection.execute()
method in conjunction with the Insert
construct, the
Connection
ensures that the column names which are passed
will be expressed in the VALUES clause of the Insert
construct automatically.
Deep Alchemy
Hi, welcome to the first edition of Deep Alchemy. The person on the left is known as The Alchemist, and you’ll note they are not a wizard, as the pointy hat is not sticking upwards. The Alchemist comes around to describe things that are generally more advanced and/or tricky and additionally not usually needed, but for whatever reason they feel you should know about this thing that SQLAlchemy can do.
In this edition, towards the goal of having some interesting data in the
address_table
as well, below is a more advanced example illustrating
how the Insert.values()
method may be used explicitly while at
the same time including for additional VALUES generated from the
parameters. A scalar subquery is constructed, making use of the
select()
construct introduced in the next section, and the
parameters used in the subquery are set up using an explicit bound
parameter name, established using the bindparam()
construct.
This is some slightly deeper alchemy just so that we can add related
rows without fetching the primary key identifiers from the user_table
operation into the application. Most Alchemists will simply use the ORM
which takes care of things like this for us.
>>> from sqlalchemy import select, bindparam
>>> scalar_subq = (
... select(user_table.c.id)
... .where(user_table.c.name == bindparam("username"))
... .scalar_subquery()
... )
>>> with engine.connect() as conn:
... result = conn.execute(
... insert(address_table).values(user_id=scalar_subq),
... [
... {"username": "spongebob", "email_address": "spongebob@sqlalchemy.org"},
... {"username": "sandy", "email_address": "sandy@sqlalchemy.org"},
... {"username": "sandy", "email_address": "sandy@squirrelpower.org"},
... ],
... )
... conn.commit()
BEGIN (implicit)
INSERT INTO address (user_id, email_address) VALUES ((SELECT user_account.id
FROM user_account
WHERE user_account.name = ?), ?)
[...] (('spongebob', 'spongebob@sqlalchemy.org'), ('sandy', 'sandy@sqlalchemy.org'),
('sandy', 'sandy@squirrelpower.org'))
COMMIT
INSERT…FROM SELECT¶
The Insert
construct can compose
an INSERT that gets rows directly from a SELECT using the Insert.from_select()
method:
>>> select_stmt = select(user_table.c.id, user_table.c.name + "@aol.com")
>>> insert_stmt = insert(address_table).from_select(
... ["user_id", "email_address"], select_stmt
... )
>>> print(insert_stmt)
INSERT INTO address (user_id, email_address)
SELECT user_account.id, user_account.name || :name_1 AS anon_1
FROM user_account
INSERT…RETURNING¶
The RETURNING clause for supported backends is used
automatically in order to retrieve the last inserted primary key value
as well as the values for server defaults. However the RETURNING clause
may also be specified explicitly using the Insert.returning()
method; in this case, the Result
object that’s returned when the statement is executed has rows which
can be fetched:
>>> insert_stmt = insert(address_table).returning(
... address_table.c.id, address_table.c.email_address
... )
>>> print(insert_stmt)
INSERT INTO address (id, user_id, email_address)
VALUES (:id, :user_id, :email_address)
RETURNING address.id, address.email_address
It can also be combined with Insert.from_select()
,
as in the example below that builds upon the example stated in
INSERT…FROM SELECT:
>>> select_stmt = select(user_table.c.id, user_table.c.name + "@aol.com")
>>> insert_stmt = insert(address_table).from_select(
... ["user_id", "email_address"], select_stmt
... )
>>> print(insert_stmt.returning(address_table.c.id, address_table.c.email_address))
INSERT INTO address (user_id, email_address)
SELECT user_account.id, user_account.name || :name_1 AS anon_1
FROM user_account RETURNING address.id, address.email_address
Tip
The RETURNING feature is also supported by UPDATE and DELETE statements,
which will be introduced later in this tutorial.
The RETURNING feature is generally [1] only
supported for statement executions that use a single set of bound
parameters; that is, it wont work with the “executemany” form introduced
at Sending Multiple Parameters. Additionally, some dialects
such as the Oracle dialect only allow RETURNING to return a single row
overall, meaning it won’t work with “INSERT..FROM SELECT” nor will it
work with multiple row Update
or Delete
forms.
See also
Insert
- in the SQL Expression API documentation