How to check if table exists?
Question:
I’m using this function :
def checker(name,s)
MY_T = "SELECT count(*) FROM `"+session.SessionInfo.Name where EventName='"+name+"'"
I want to check if the table exists, how can I do it?
I saw some examples using XXXX.execute()
. What does it mean?
Here is what I saw:
query = cursor.execute("""SELECT count(*) FROM scan WHERE prefix = %s and code_id = %s and answer = %s and station_id = %s""",
(prefix, code_id, answer, station,))
if query != 1:
I tried printing MY_T to see if it returns -1 for example but it just prints "select count (*)...... "
How can I check it?
Answers:
Use the “TABLES” information schema view.
http://dev.mysql.com/doc/refman/5.0/en/information-schema.html
SELECT * FROM information_schema.tables
WHERE table_name = 'YOUR TABLE'
You can apply this view to your code by doing something like the following:
def checkTableExists(dbcon, tablename):
dbcur = dbcon.cursor()
dbcur.execute("""
SELECT COUNT(*)
FROM information_schema.tables
WHERE table_name = '{0}'
""".format(tablename.replace(''', '''')))
if dbcur.fetchone()[0] == 1:
dbcur.close()
return True
dbcur.close()
return False
If you are using Python-MySQL (MySQLdb) -> http://mysql-python.sourceforge.net/MySQLdb.html
cursor.execute() is the method to run queries with MySQLdb, Python MySQL driver. You can pass two arguments, like:
cursor.execute(statement, parameters)
And will execute “statement” parsing “parameters” to the statement. You need to have opened a database connection and also open a cursor
I think you can use MySQL’s statement: SHOW TABLES LIKE ‘tablename’;
stmt = "SHOW TABLES LIKE 'tableName'"
cursor.execute(stmt)
result = cursor.fetchone()
if result:
# there is a table named "tableName"
else:
# there are no tables named "tableName"
EDIT: there will other Python drivers with similar behaviour. Look for yours 🙂
I found that this works well with Python 3.6 and MySql 5.7:
table = 'myTable'
_SQL = """SHOW TABLES"""
cursor.execute(_SQL)
results = cursor.fetchall()
print('All existing tables:', results) # Returned as a list of tuples
results_list = [item[0] for item in results] # Conversion to list of str
if table in results_list:
print(table, 'was found!')
else:
print(table, 'was NOT found!')
Above answer might not work for Oracle, I found code snippet below work for Oracle:
import cx_Oracle
def checkTableExists(dbcon, tablename):
dbcur = dbcon.cursor()
try:
dbcur.execute("SELECT * FROM {}".format(tablename))
return True
except cx_Oracle.DatabaseError as e:
x = e.args[0]
if x.code == 942: ## Only catch ORA-00942: table or view does not exist error
return False
else:
raise e
finally:
dbcur.close()
I think the most straightforward way is using:
SELECT COUNT(*) = 1 as exists FROM pg_tables WHERE tablename = 'my_table';
that returns if table exists:
exists
--------
t
(1 row)
or in Python using psycopg2
:
cur.execute(
"""
SELECT COUNT(*) = 1 FROM pg_tables WHERE tablename = 'my_table';
"""
)
exists = cur.fetchone()[0]
print(exists)
True
if exists is False:
# table does not exist
...
try this code
it shows all tables. then, compare the saved tables name to your target table
change cursor to yours in your code ^_^
def tableExistance(table_name):
cursor.execute('SHOW tables;')
myresult = cursor.fetchall()
for loacal_table_name in myresult:
print('table name', loacal_table_name[0])
if loacal_table_name[0] == table_name:
return True
return False
exist = tableExistance("you table name")
print('tableExistance', exist)
I’m using this function :
def checker(name,s)
MY_T = "SELECT count(*) FROM `"+session.SessionInfo.Name where EventName='"+name+"'"
I want to check if the table exists, how can I do it?
I saw some examples using XXXX.execute()
. What does it mean?
Here is what I saw:
query = cursor.execute("""SELECT count(*) FROM scan WHERE prefix = %s and code_id = %s and answer = %s and station_id = %s""",
(prefix, code_id, answer, station,))
if query != 1:
I tried printing MY_T to see if it returns -1 for example but it just prints "select count (*)...... "
How can I check it?
Use the “TABLES” information schema view.
http://dev.mysql.com/doc/refman/5.0/en/information-schema.html
SELECT * FROM information_schema.tables
WHERE table_name = 'YOUR TABLE'
You can apply this view to your code by doing something like the following:
def checkTableExists(dbcon, tablename):
dbcur = dbcon.cursor()
dbcur.execute("""
SELECT COUNT(*)
FROM information_schema.tables
WHERE table_name = '{0}'
""".format(tablename.replace(''', '''')))
if dbcur.fetchone()[0] == 1:
dbcur.close()
return True
dbcur.close()
return False
If you are using Python-MySQL (MySQLdb) -> http://mysql-python.sourceforge.net/MySQLdb.html
cursor.execute() is the method to run queries with MySQLdb, Python MySQL driver. You can pass two arguments, like:
cursor.execute(statement, parameters)
And will execute “statement” parsing “parameters” to the statement. You need to have opened a database connection and also open a cursor
I think you can use MySQL’s statement: SHOW TABLES LIKE ‘tablename’;
stmt = "SHOW TABLES LIKE 'tableName'"
cursor.execute(stmt)
result = cursor.fetchone()
if result:
# there is a table named "tableName"
else:
# there are no tables named "tableName"
EDIT: there will other Python drivers with similar behaviour. Look for yours 🙂
I found that this works well with Python 3.6 and MySql 5.7:
table = 'myTable'
_SQL = """SHOW TABLES"""
cursor.execute(_SQL)
results = cursor.fetchall()
print('All existing tables:', results) # Returned as a list of tuples
results_list = [item[0] for item in results] # Conversion to list of str
if table in results_list:
print(table, 'was found!')
else:
print(table, 'was NOT found!')
Above answer might not work for Oracle, I found code snippet below work for Oracle:
import cx_Oracle
def checkTableExists(dbcon, tablename):
dbcur = dbcon.cursor()
try:
dbcur.execute("SELECT * FROM {}".format(tablename))
return True
except cx_Oracle.DatabaseError as e:
x = e.args[0]
if x.code == 942: ## Only catch ORA-00942: table or view does not exist error
return False
else:
raise e
finally:
dbcur.close()
I think the most straightforward way is using:
SELECT COUNT(*) = 1 as exists FROM pg_tables WHERE tablename = 'my_table';
that returns if table exists:
exists
--------
t
(1 row)
or in Python using psycopg2
:
cur.execute(
"""
SELECT COUNT(*) = 1 FROM pg_tables WHERE tablename = 'my_table';
"""
)
exists = cur.fetchone()[0]
print(exists)
True
if exists is False:
# table does not exist
...
try this code
it shows all tables. then, compare the saved tables name to your target table
change cursor to yours in your code ^_^
def tableExistance(table_name):
cursor.execute('SHOW tables;')
myresult = cursor.fetchall()
for loacal_table_name in myresult:
print('table name', loacal_table_name[0])
if loacal_table_name[0] == table_name:
return True
return False
exist = tableExistance("you table name")
print('tableExistance', exist)