I am very new to sql and intermediate at python. Using sqlite3, how can I get a print() list of of primary and foreign keys (per table) in my database?
Using Python2.7, SQLite3, PyCharm.
sqlite3.version = 2.6.0
sqlite3.sqlite_version = 3.8.11
Also note: when I set up the database, I enabled FKs as such:
conn = sqlite3.connect(db_file)
conn.execute('pragma foreign_keys=ON')
I tried the following:
conn=sqlite3.connect(db_path)
print(conn.execute("PRAGMA table_info"))
print(conn.execute("PRAGMA foreign_key_list"))
Which returned:
<sqlite3.Cursor object at 0x0000000002FCBDC0>
<sqlite3.Cursor object at 0x0000000002FCBDC0>
I also tried the following, which prints nothing (but I think this may be because it's a dummy database with tables and fields but no records):
conn=sqlite3.connect(db_path)
rows = conn.execute('PRAGMA table_info')
for r in rows:
print r
rows2 = conn.execute('PRAGMA foreign_key_list')
for r2 in rows2:
print r2
Unknown or malformed PRAGMA statements are ignored.
The problem with your PRAGMAs is that the table name is missing. You have to get a list of all tables, and then execute those PRAGMAs for each one:
rows = db.execute("SELECT name FROM sqlite_master WHERE type = 'table'")
tables = [row[0] for row in rows]
def sql_identifier(s):
return '"' + s.replace('"', '""') + '"'
for table in tables:
print("table: " + table)
rows = db.execute("PRAGMA table_info({})".format(sql_identifier(table)))
print(rows.fetchall())
rows = db.execute("PRAGMA foreign_key_list({})".format(sql_identifier(table)))
print(rows.fetchall())
SELECT
name
FROM
sqlite_master
WHERE
type ='table' AND
name NOT LIKE 'sqlite_%';
this sql will show all table in database, for eache table run sql PRAGMA table_info(your_table_name);, you can get the primary key of the table.
Those pictures show what sql result like in my database:
first sql result
second sql result
Related
I got lots of example to append/overwrite table in sql from AZ Databricks Notebook. But no single way to directly update, insert data using query or otherway.
ex. I want to update all row where (identity column)ID = 1143, so steps which I need to taken care are
val srMaster = "(SELECT ID, userid,statusid,bloburl,changedby FROM SRMaster WHERE ID = 1143) srMaster"
val srMasterTable = spark.read.jdbc(url=jdbcUrl, table=srMaster,
properties=connectionProperties)
srMasterTable.createOrReplaceTempView("srMasterTable")
val srMasterTableUpdated = spark.sql("SELECT userid,statusid,bloburl,140 AS changedby FROM srMasterTable")
import org.apache.spark.sql.SaveMode
srMasterTableUpdated.write.mode(SaveMode.Overwrite)
.jdbc(jdbcUrl, "[dbo].[SRMaster]", connectionProperties)
Is there any other sufficient way to achieve the same.
Note : Above code is also not working as SQLServerException: Could not drop object 'dbo.SRMaster' because it is referenced by a FOREIGN KEY constraint. , so it look like it drop table and recreate...not at all the solution.
You can use insert using a FROM statement.
Example: update values from another table in this table where a column matches.
INSERT INTO srMaster
FROM srMasterTable SELECT userid,statusid,bloburl,140 WHERE ID = 1143;
or
insert new values to rows where one of the existing column value matches
UPDATE srMaster SET userid = 1, statusid = 2, bloburl = 'https://url', changedby ='user' WHERE ID = '1143'
or just insert multiple values
INSERT INTO srMaster VALUES
(1, 10, 'https://url1','user1'),
(2, 11, 'https://url2','user2');
In SQL Server, you cannot drop a table if it is referenced by a FOREIGN KEY constraint. You have to either drop the child tables before removing the parent table, or remove foreign key constraints.
For a parent table, you can use the below query to get foreign key constraint names and the referencing table names:
SELECT name AS 'Foreign Key Constraint Name',
OBJECT_SCHEMA_NAME(parent_object_id) + '.' + OBJECT_NAME(parent_object_id) AS 'Child Table'
FROM sys.foreign_keys
WHERE OBJECT_SCHEMA_NAME(referenced_object_id) = 'dbo' AND
OBJECT_NAME(referenced_object_id) = 'PARENT_TABLE'
Then you can alter the child table and drop the constraint by its name using the below statement:
ALTER TABLE dbo.childtable DROP CONSTRAINT FK_NAME;
I have searched for the solution to this problem for a long time, but I haven't got the appropriate method.
Basically All I have is tons of tables, and I want to query value from different tables using raw SQL.
In Django, we need a class representing a table to perform the query, for example:
Routes.objects.raw("SELECT * FROM routes")
In this way, I can only query a table, but what if I want to query different tables based on the user's input?
I'm new to Django, back in ASP.NET we can simply do the following query:
string query = "SELECT * FROM " + county + " ;";
var bus = _context.Database.SqlQuery<keelung>(query).ToList();
Is this case, I can do the query directly on the database instead of the model class, and I can select the table based on the user's selection.
Is there any method to achieve this with Django?
You can run raw queries in Django like this -
From django.db import connection
cursor = connection.cursor()
table = my_table;
cursor.execute("Select * from " + table)
data = cursor.fetchall()
I intend to create a table in sqlite3 with the column names in a list [item1,...]. I don't want to hard code the column names while creating the table because the number of columns and even names are dynamic. I want the correct syntax to get the column names directly from this list. Thank you. I'm using python.
You can do something like this:
import contextlib
import sqlite3
fields = ["field1", "field2", "field3"]
with contextlib.closing(sqlite3.connect(':memory:')) as conn:
cursor = conn.cursor()
columns = ", ".join("{field} TEXT".format(field=field) for field in fields)
cursor.execute("""
CREATE TABLE IF NOT EXISTS your_table(
id INTEGER PRIMARY KEY AUTOINCREMENT UNIQUE,
{columns}
)
""".format(columns=columns))
conn.commit()
But, you should consider using an ORM, like SqlAlchemy. Here is a tutorial for that: https://www.pythoncentral.io/introductory-tutorial-python-sqlalchemy/
Edit
To go further, your insert statement could be built like this:
stmt = ("INSERT INTO mytable ({fields}) VALUES ({marks})"
.format(fields=", ".join(fields), marks=", ".join("?" * len(fields))))
For instance:
INSERT INTO mytable (field1, field2, field3) VALUES (?, ?, ?)
Here's how I can do it when MySQL is the backend,
cursor.execute('show tables')
rows = cursor.fetchall()
for row in rows:
cursor.execute('drop table %s; ' % row[0])
But how can I do it when postgresql is the backend?
cursor.execute("""SELECT table_name FROM information_schema.tables WHERE table_schema='public' AND table_type != 'VIEW' AND table_name NOT LIKE 'pg_ts_%%'""")
rows = cursor.fetchall()
for row in rows:
try:
cursor.execute('drop table %s cascade ' % row[0])
print "dropping %s" % row[0]
except:
print "couldn't drop %s" % row[0]
Courtesy of http://www.siafoo.net/snippet/85
You can use select * from pg_tables; get get a list of tables, although you probably want to exclude where schemaname <> 'pg_catalog'...
Based on another one of your recent questions, if you're trying to just drop all your django stuff, but don't have permission to drop the DB, can you just DROP the SCHEMA that Django has everything in?
Also on your drop, use CASCADE.
EDIT: Can you select * from information_schema.tables; ?
EDIT: Your column should be row[2] instead of row[0] and you need to specify which schema to look at with a WHERE schemaname = 'my_django_schema_here' clause.
EDIT: Or just SELECT table_name from pg_tables where schemaname = 'my_django_schema_here'; and row[0]
Documentation says that ./manage.py sqlclear Prints the DROP TABLE SQL statements for the given app name(s).
I use this script to clear the tables, I put it in a script called phoenixdb.sh because it burns the DB down and a new one rises from the ashes. I use this to prevent lots of migrations in the early dev portion of the project.
set -e
python manage.py dbshell <<EOF
DROP SCHEMA public CASCADE;
CREATE SCHEMA public;
EOF
python manage.py migrate
This wipes the tables from the db without deleting the db. Your Django user will need to own the schema though which you can setup with:
alter schema public owner to django-db-user-name;
And you might want to change the owner of the db as well
alter database django-db-name owner to django-db-user-name;
\dt is the equivalent command in postgres to list tables. Each row will contain values for (schema, Name, Type, Owner), so you have to use the second (row[1]) value.
Anyway, you solution will break (in MySQL and PostgreSQL) when foreign-key constraints are involved, and if there aren't any, you might get troubles with the sequences. So the best way is in my opinion to simply drop the whole database and call initdb again (which is also the more efficient solution).
I'm using the sqlite3 library in c++ to query the database from *.sqlite file. can you write a query statement in sqlite3 like:
char* sql = "select name from table id = (select full_name from second_table where column = 4);"
The second statement should return an id to complete the query statement with first statement.
Yes you can, just make sure that the nested query doesn't return more than one row. Add a LIMIT 1 to the end of the nested query to fix this. Also make sure that it always returns a row, or else the main query will not work.
If you want to match several rows in the nested query, then you can use either IN, like so:
char* sql = "select name from table WHERE id IN (select full_name from second_table where column = 4);"
or you can use JOIN:
char* sql = "select name from table JOIN second_table ON table.id = second_table.full_name WHERE second_table.column = 4"
Note that the IN method can be very slow, and that JOIN can be very fast, if you index on the right columns
On a sidenote, you can use SQLiteadmin (http://sqliteadmin.orbmu2k.de/) to view the database and make queries directly in it (useful for testing etc).