Declare @SumVal int; Select @SumVal=Sum(Amount) From Expense; Print @SumVal; You can, of course, print any number of fields from the table in this way. Of course, if you want to print all of the results from a query that returns multiple rows, you'd just direct your output appropriately (e.g. to Text).
As the documentation says, all() returns the result of the query as a list.
The select() method of table object enables us to construct SELECT expression. The resultant variable is an equivalent of cursor in DBAPI. We can now fetch records using fetchone() method. Here, we have to note that select object can also be obtained by select() function in sqlalchemy.
first() applies a limit of one within the generated SQL, so that only one primary entity row is generated on the server side (note this may consist of multiple result rows if join-loaded collections are present). Calling Query. first() results in an execution of the underlying query.
In the vast majority of cases, the "stringification" of a SQLAlchemy statement or query is as simple as:
print(str(statement))
This applies both to an ORM Query
as well as any select()
or other statement.
Note: the following detailed answer is being maintained on the sqlalchemy documentation.
To get the statement as compiled to a specific dialect or engine, if the statement itself is not already bound to one you can pass this in to compile():
print(statement.compile(someengine))
or without an engine:
from sqlalchemy.dialects import postgresql
print(statement.compile(dialect=postgresql.dialect()))
When given an ORM Query
object, in order to get at the compile()
method we only need access the .statement accessor first:
statement = query.statement
print(statement.compile(someengine))
with regards to the original stipulation that bound parameters are to be "inlined" into the final string, the challenge here is that SQLAlchemy normally is not tasked with this, as this is handled appropriately by the Python DBAPI, not to mention bypassing bound parameters is probably the most widely exploited security holes in modern web applications. SQLAlchemy has limited ability to do this stringification in certain circumstances such as that of emitting DDL. In order to access this functionality one can use the 'literal_binds' flag, passed to compile_kwargs
:
from sqlalchemy.sql import table, column, select
t = table('t', column('x'))
s = select([t]).where(t.c.x == 5)
print(s.compile(compile_kwargs={"literal_binds": True}))
the above approach has the caveats that it is only supported for basic
types, such as ints and strings, and furthermore if a bindparam
without a pre-set value is used directly, it won't be able to
stringify that either.
To support inline literal rendering for types not supported, implement
a TypeDecorator
for the target type which includes a
TypeDecorator.process_literal_param
method:
from sqlalchemy import TypeDecorator, Integer
class MyFancyType(TypeDecorator):
impl = Integer
def process_literal_param(self, value, dialect):
return "my_fancy_formatting(%s)" % value
from sqlalchemy import Table, Column, MetaData
tab = Table('mytable', MetaData(), Column('x', MyFancyType()))
print(
tab.select().where(tab.c.x > 5).compile(
compile_kwargs={"literal_binds": True})
)
producing output like:
SELECT mytable.x
FROM mytable
WHERE mytable.x > my_fancy_formatting(5)
Given that what you want makes sense only when debugging, you could start SQLAlchemy with echo=True
, to log all SQL queries. For example:
engine = create_engine(
"mysql://scott:tiger@hostname/dbname",
encoding="latin1",
echo=True,
)
This can also be modified for just a single request:
echo=False
– ifTrue
, the Engine will log all statements as well as arepr()
of their parameter lists to the engines logger, which defaults tosys.stdout
. Theecho
attribute ofEngine
can be modified at any time to turn logging on and off. If set to the string"debug"
, result rows will be printed to the standard output as well. This flag ultimately controls a Python logger; see Configuring Logging for information on how to configure logging directly.Source: SQLAlchemy Engine Configuration
If used with Flask, you can simply set
app.config["SQLALCHEMY_ECHO"] = True
to get the same behaviour.
This works in python 2 and 3 and is a bit cleaner than before, but requires SA>=1.0.
from sqlalchemy.engine.default import DefaultDialect
from sqlalchemy.sql.sqltypes import String, DateTime, NullType
# python2/3 compatible.
PY3 = str is not bytes
text = str if PY3 else unicode
int_type = int if PY3 else (int, long)
str_type = str if PY3 else (str, unicode)
class StringLiteral(String):
"""Teach SA how to literalize various things."""
def literal_processor(self, dialect):
super_processor = super(StringLiteral, self).literal_processor(dialect)
def process(value):
if isinstance(value, int_type):
return text(value)
if not isinstance(value, str_type):
value = text(value)
result = super_processor(value)
if isinstance(result, bytes):
result = result.decode(dialect.encoding)
return result
return process
class LiteralDialect(DefaultDialect):
colspecs = {
# prevent various encoding explosions
String: StringLiteral,
# teach SA about how to literalize a datetime
DateTime: StringLiteral,
# don't format py2 long integers to NULL
NullType: StringLiteral,
}
def literalquery(statement):
"""NOTE: This is entirely insecure. DO NOT execute the resulting strings."""
import sqlalchemy.orm
if isinstance(statement, sqlalchemy.orm.Query):
statement = statement.statement
return statement.compile(
dialect=LiteralDialect(),
compile_kwargs={'literal_binds': True},
).string
Demo:
# coding: UTF-8
from datetime import datetime
from decimal import Decimal
from literalquery import literalquery
def test():
from sqlalchemy.sql import table, column, select
mytable = table('mytable', column('mycol'))
values = (
5,
u'snowman: ☃',
b'UTF-8 snowman: \xe2\x98\x83',
datetime.now(),
Decimal('3.14159'),
10 ** 20, # a long integer
)
statement = select([mytable]).where(mytable.c.mycol.in_(values)).limit(1)
print(literalquery(statement))
if __name__ == '__main__':
test()
Gives this output: (tested in python 2.7 and 3.4)
SELECT mytable.mycol
FROM mytable
WHERE mytable.mycol IN (5, 'snowman: ☃', 'UTF-8 snowman: ☃',
'2015-06-24 18:09:29.042517', 3.14159, 100000000000000000000)
LIMIT 1
We can use compile method for this purpose. From the docs:
from sqlalchemy.sql import text
from sqlalchemy.dialects import postgresql
stmt = text("SELECT * FROM users WHERE users.name BETWEEN :x AND :y")
stmt = stmt.bindparams(x="m", y="z")
print(stmt.compile(dialect=postgresql.dialect(),compile_kwargs={"literal_binds": True}))
Result:
SELECT * FROM users WHERE users.name BETWEEN 'm' AND 'z'
Warning from docs:
Never use this technique with string content received from untrusted input, such as from web forms or other user-input applications. SQLAlchemy’s facilities to coerce Python values into direct SQL string values are not secure against untrusted input and do not validate the type of data being passed. Always use bound parameters when programmatically invoking non-DDL SQL statements against a relational database.
So building on @zzzeek's comments on @bukzor's code I came up with this to easily get a "pretty-printable" query:
def prettyprintable(statement, dialect=None, reindent=True):
"""Generate an SQL expression string with bound parameters rendered inline
for the given SQLAlchemy statement. The function can also receive a
`sqlalchemy.orm.Query` object instead of statement.
can
WARNING: Should only be used for debugging. Inlining parameters is not
safe when handling user created data.
"""
import sqlparse
import sqlalchemy.orm
if isinstance(statement, sqlalchemy.orm.Query):
if dialect is None:
dialect = statement.session.get_bind().dialect
statement = statement.statement
compiled = statement.compile(dialect=dialect,
compile_kwargs={'literal_binds': True})
return sqlparse.format(str(compiled), reindent=reindent)
I personally have a hard time reading code which is not indented so I've used sqlparse
to reindent the SQL. It can be installed with pip install sqlparse
.
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