In class, we got a code to Orient a SQLite database. I kind of get the code (below), but want to get a conceptual understanding of what "Orient" means.
import sqlite3
conn = sqlite3.connect('example3.db')
c = conn.cursor()
c.execute('SELECT name FROM sqlite_master WHERE type=\'table\'') #list all tables therein
print c.fetchall()
c.execute('SELECT sql FROM sqlite_master WHERE type=\'table\' AND name=\'students\'') #list columns in table 'students'
print c.fetchall()
conn.close()
Related
Ok I am new to sqlite and python in general so please be nice =)
I have a simple dictionary -
time = data[0]['timestamp']
price = data[0]['price']
myprice = {'Date':time,'price':price}
myprice looks like this (time is a timestamp) -
{'Date': 1553549093, 'price': 1.7686}
I now want to add the data to sqlite3 database...so I created this -
#Create database if not exist...
db_filename = 'mydb_test.db'
connection = sqlite3.connect(db_filename)
#Get a SQL cursor to be able to execute SQL commands...
cursor = connection.cursor()
#Create table
sql = '''CREATE TABLE IF NOT EXISTS TEST
(PID INTEGER PRIMARY KEY AUTOINCREMENT,
DATE TIMESTAMP,
PRICE FLOAT)'''
#Now lets execute the above SQL
cursor.execute(sql)
#Insert data in sql
sql2 = ("INSERT INTO GBPCAD VALUES (?,?)", [(myprice['Date'],myprice['price'])])
cursor.execute(sql2)
cursor.commit()
connection.close()
But when executing this code I get ValueError: operation parameter must be str
What am I doing wrong?
Pass the arguments of the insert statement in execute():
sql2 = "INSERT INTO GBPCAD (DATE, PRICE) VALUES (?,?)"
cursor.execute(sql2, (myprice['Date'], myprice['price']))
Also include in the insert statement the names of the columns.
The following piece of code creates two databases:
import sqlite3
db = 'brazil'
conn = sqlite3.connect(db+'.db')
c = conn.cursor()
qCreate = """
CREATE TABLE states
(zip_id numeric NOT NULL,
state_name text NOT NULL,
CONSTRAINT pk_brazil
PRIMARY KEY (zip_id) """
c.execute(qCreate)
conn.commit()
conn.close()
db = 'city'
conn = sqlite3.connect(db+'.db')
c = conn.cursor()
qCreate = """CREATE TABLE rio_de_janeiro
(zip_id numeric NOT NULL,
beach_name text NOT NULL,
CONSTRAINT pk_rio
PRIMARY KEY (zip_id)
"""
c.execute(qCreate)
conn.commit()
conn.close()
The following piece of code attaches the database RIO to the database BRAZIL and prints all the databases (Rio and Brazil).
db = 'brazil'
conn = sqlite3.connect(db+'.db')
c = conn.cursor()
qCreate = """ATTACH DATABASE ? AS competition """
c.execute(qCreate, ('rio.db',))
c.execute("PRAGMA database_list")
data = c.fetchall()
print data
conn.commit()
conn.close()
However the following piece of code prints only Brazil database:
db = 'brazil'
conn = sqlite3.connect(db+'.db')
c = conn.cursor()
c.execute("PRAGMA database_list")
data = c.fetchall()
print data
conn.commit()
conn.close()
The attached database is no longer attached.
The sqlite3 documentation hints on these lines:
The ATTACH DATABASE statement adds another database file to the current database connection.
Do I have to attach the database every time?
I planed to use attached databases for schemas, but maybe I should try something else?
I am using python in Pythonista App in iOS
Almost all settings you can change in SQLite apply only to the current connection, i.e., are not saved in the database file.
So you have to re-ATTACH any databases whenever you have re-opened the main database.
Using attached databases makes sense only if you must use multiple database files due to some external constraint. In most cases, you should use only a single database.
SQLite does not have schemas. If you want to emulate them with attached databases, you have to live with the limitations of that approach.
I need to get column names and their tables in a SQLite database. What I need is a resultset with 2 columns: table_name | column_name.
In MySQL, I'm able to get this information with a SQL query on database INFORMATION_SCHEMA. However the SQLite offers table sqlite_master:
sqlite> create table students (id INTEGER, name TEXT);
sqlite> select * from sqlite_master;
table|students|students|2|CREATE TABLE students (id INTEGER, name TEXT)
which results a DDL construction query (CREATE TABLE) which is not helpful for me and I need to parse this to get relevant information.
I need to get list of tables and join them with columns or just get columns along with table name column. So PRAGMA table_info(TABLENAME) is not working for me since I don't have table name. I want to get all column metadata in the database.
Is there a better way to get that information as a result set by querying database?
You've basically named the solution in your question.
To get a list of tables (and views), query sqlite_master as in
SELECT name, sql FROM sqlite_master
WHERE type='table'
ORDER BY name;
(see the SQLite FAQ)
To get information about the columns in a specific table, use PRAGMA table_info(table-name); as explained in the SQLite PRAGMA documentation.
I don't know of any way to get tablename|columnname returned as the result of a single query. I don't believe SQLite supports this. Your best bet is probably to use the two methods together to return the information you're looking for - first get the list of tables using sqlite_master, then loop through them to get their columns using PRAGMA table_info().
Recent versions of SQLite allow you to select against PRAGMA results now, which makes this easy:
SELECT
m.name as table_name,
p.name as column_name
FROM
sqlite_master AS m
JOIN
pragma_table_info(m.name) AS p
ORDER BY
m.name,
p.cid
where p.cid holds the column order of the CREATE TABLE statement, zero-indexed.
David Garoutte answered this here, but this SQL should execute faster, and columns are ordered by the schema, not alphabetically.
Note that table_info also contains
type (the datatype, like integer or text),
notnull (1 if the column has a NOT NULL constraint)
dflt_value (NULL if no default value)
pk (1 if the column is the table's primary key, else 0)
RTFM: https://www.sqlite.org/pragma.html#pragma_table_info
There are ".tables" and ".schema [table_name]" commands which give kind of a separated version to the result you get from "select * from sqlite_master;"
There is also "pragma table_info([table_name]);" command to get a better result for parsing instead of a construction query:
sqlite> .tables
students
sqlite> .schema students
create table students(id INTEGER, name TEXT);
sqlite> pragma table_info(students);
0|id|INTEGER|0||0
1|name|TEXT|0||0
Hope, it helps to some extent...
Another useful trick is to first get all the table names from sqlite_master.
Then for each one, fire off a query "select * from t where 1 = 0". If you analyze the structure of the resulting query - depends on what language/api you're calling it from - you get a rich structure describing the columns.
In python
c = ...db.cursor()
c.execute("select * from t where 1=0");
c.fetchall();
print c.description;
Juraj
PS. I'm in the habit of using 'where 1=0' because the record limiting syntax seems to vary from db to db. Furthermore, a good database will optimize out this always-false clause.
The same effect, in SQLite, is achieved with 'limit 0'.
FYI, if you're using .Net you can use the DbConnection.GetSchema method to retrieve information that usually is in INFORMATION_SCHEMA. If you have an abstraction layer you can have the same code for all types of databases (NOTE that MySQL seems to swich the 1st 2 arguments of the restrictions array).
Try this sqlite table schema parser, I implemented the sqlite table parser for parsing the table definitions in PHP.
It returns the full definitions (unique, primary key, type, precision, not null, references, table constraints... etc)
https://github.com/maghead/sqlite-parser
The syntax follows sqlite create table statement syntax: http://www.sqlite.org/lang_createtable.html
This is an old question but because of the number of times it has been viewed we are adding to the question for the simple reason most of the answers tell you how to find the TABLE names in the SQLite Database
WHAT DO YOU DO WHEN THE TABLE NAME IS NOT IN THE DATABASE ?
This is happening to our app because we are creating TABLES programmatically
So the code below will deal with the issue when the TABLE is NOT in or created by the Database Enjoy
public void toPageTwo(View view){
if(etQuizTable.getText().toString().equals("")){
Toast.makeText(getApplicationContext(), "Enter Table Name\n\n"
+" OR"+"\n\nMake Table First", Toast.LENGTH_LONG
).show();
etQuizTable.requestFocus();
return;
}
NEW_TABLE = etQuizTable.getText().toString().trim();
db = dbHelper.getWritableDatabase();
ArrayList<String> arrTblNames = new ArrayList<>();
Cursor c = db.rawQuery("SELECT name FROM sqlite_master WHERE
type='table'", null);
if (c.moveToFirst()) {
while ( !c.isAfterLast() ) {
arrTblNames.add( c.getString( c.getColumnIndex("name")) );
c.moveToNext();
}
}
c.close();
db.close();
boolean matchFound = false;
for(int i=0;i<arrTblNames.size();i++) {
if(arrTblNames.get(i).equals(NEW_TABLE)) {
Intent intent = new Intent(ManageTables.this, TableCreate.class
);
startActivity( intent );
matchFound = true;
}
}
if (!matchFound) {
Toast.makeText(getApplicationContext(), "No Such Table\n\n"
+" OR"+"\n\nMake Table First", Toast.LENGTH_LONG
).show();
etQuizTable.requestFocus();
}
}
How can I get the list of all the available tables in sqlite programmatically?
try this :
SELECT * FROM sqlite_master where type='table';
Use the below sql statement to get list of all table in sqllite data base
SELECT * FROM dbname.sqlite_master WHERE type='table';
The same question asked before on StackOverFlow.
How to list the tables in an SQLite database file that was opened with ATTACH?
worked for me
SELECT * FROM sqlite_master where type='table'
con = sqlite3.connect('db.sqlite')
cur = con.cursor()
cur.execute('''
SELECT tbl_name
FROM sqlite_master
WHERE type = 'table';
''')
print(cur.fetchall())
I am looking to retrieve a list of columns in a table. The database is the latest release of SQLite (3.6, I believe). I am looking for code that does this with a SQL query. Extra bonus points for metadata related to the columns (e.g. length, data type, etc...)
What you're looking for is called the data dictionary. In sqlite a list of all tables can be found by querying sqlite_master table (or view?)
sqlite> create table people (first_name varchar, last_name varchar, email_address varchar);
sqlite> select * from sqlite_master;
table|people|people|2|CREATE TABLE people (first_name varchar, last_name varchar, email_address varchar)
To get column information you can use the pragma table_info(table_name) statement:
sqlite> pragma table_info(people);
0|first_name|varchar|0||0
1|last_name|varchar|0||0
2|email_address|varchar|0||0
For more information on the pragma statements, see the documentation.
Here's the simple way:
.schema <table>
The question is old but the following hasn't been mentioned yet.
Another convenient way in many cases is to turn headers on by:
sqlite> .headers on
Then,
sqlite> SELECT ... FROM table
will display a headline showing all selected fields (all if you SELECT *) at the top of the output.
Here's a SELECT statement that lists all tables and columns in the current database:
SELECT m.name as tableName,
p.name as columnName
FROM sqlite_master m
left outer join pragma_table_info((m.name)) p
on m.name <> p.name
order by tableName, columnName
;
just go into your sqlite shell:
$ sqlite3 path/to/db.sqlite3
and then just hit
sqlite> .schema
and you will get everything.
This is a query that lists all tables with their columns, and all the metadata I could get about each column as OP requested (as bonus points).
SELECT
m.name AS table_name,
p.cid AS col_id,
p.name AS col_name,
p.type AS col_type,
p.pk AS col_is_pk,
p.dflt_value AS col_default_val,
p.[notnull] AS col_is_not_null
FROM sqlite_master m
LEFT OUTER JOIN pragma_table_info((m.name)) p
ON m.name <> p.name
WHERE m.type = 'table'
ORDER BY table_name, col_id
Thanks to #David Garoutte for showing me how to get pragma_table_info to work in a query.
Run this query to see all the table metadata:
SELECT * FROM sqlite_master WHERE type = 'table'
Building on the above, you can do it all at once:
sqlite3 yourdb.db ".schema"
That will give you the SQL to create the table, which is effectively a list of the columns.
In case if you want to get all column names into one single comma separated string, you can use below.
SELECT GROUP_CONCAT(NAME,',') FROM PRAGMA_TABLE_INFO('table_name')
Here the pragma table_info is used as pragma_table_info for the select statement and GROUP_CONCAT is to combine all the field names into one string. for the second parameter of GROUP_CONCAT you can pass the separator.
I know, it’s been a long time but it’s never too late…
I had a similar question with TCL as interpreter and after several search, found nothing good for me. So I propose something based on PRAGMA, knowing that your DB is “main”
db eval { PRAGMA main.table_info(<your table name>) } TBL { puts $TBL(name) }
And array use to obtain a list
set col_list {}
db eval { PRAGMA main.table_info(<your table name>) } TBL { lappend col_list $TBL(name) }
puts $col_list