I am using Cassandra 3.9 and DataStax C++ driver 2.6. I have created a table that has only a primary key and static columns. I am able to insert data into the table, but I am not able to update the table and I don't know why. As an example, I created the table t that is defined here:
[Cassandra Table with primary key and static column][1]
Then I successfully inserted data into the table with the following CQL insert command:
"insert into t (k, s, i) VALUES('George', 'Hello', 2);"
Then, "select * from t;" results in the following:
k | i | s
-------+---+-------
George | 2 | Hello
However, if I then try to update the table using the following command:
"UPDATE t set s = "World" where k = "George";"
I get the following error:
SyntaxException: line 1:26 no viable alternative at input 'where' (UPDATE t set s = ["Worl]d" where...)
Does anyone know how to update a table with only static columns and a primary key (i.e. partition key + cluster key)?
Enclose string with single quote
Example :
UPDATE t set s = 'World' where k = 'George';
Related
I'm using the MySQL X Dev C++ API (Not the legacy C++ connector) and I want to find the value from a row.
What I have done here is that I create my SQL query command
std::string query = "SELECT * FROM " + std::string(tableName) + " ORDER BY measurement_id DESC LIMIT 1";
Then I execute that command
mysqlx::SqlResult result = connection->sql(query).execute();
Then I check if it has data. If yes, then I fetch one row only. Notice that I can only fetch one row due to the SQL query command only ask for one row.
if (result.hasData()) {
mysqlx::Row row = result.fetchOne();
mysqlx::Value value = row.get(0); // 0 = First column in the row
}
But here is the problem. How can I get this value to the long data type?
mysqlx::Value value = row.get(0);
I have a 10GB csv file (34 million rows) with data(without column description/header) that needs to be populated in a Postgres database.
The row data has columns that need to go in different Models.
I have the following DB schema:
Currently what I do is:
Loop through rows:
Create instance B with specific columns from row and append to an array_b
Create instance C with specific columns from row and append to an array_c
Create instance A with specific columns from row and relation to B and C, and
append to an array_a
Bulk create in order: B, C and A
This works perfectly fine, however, it takes 4 hours to populate the DB.
I wanted to optimize the population and came across the psql COPY FROM command.
So I thought I would be able to do something like:
Create instance A with specific columns from the file
for foreign key to C
create instance C with specific columns from the row
for foreign key to B
create instance B with specific columns from the row
Go to 1.
After a short research on how to do that, I found out that it does not allow table manipulations while copying data (such as looking up to another table for fetching proper foreign keys to insert)
Anyone can guide me in what to look for, any other method or 'hack' on how to optimize the data population?
Thanks in advance.
Management command:
with open(settings.DATA_PATH, 'r') as file:
csvreader = csv.reader(file)
next(csvreader)
b_array = []
c_array = []
a_array = []
for row in csvreader:
some_data = row[0]
some_data = row[1]
....
b = B(
some_data=some_data
)
b_array.append(b)
c = C(
some_data=some_data
)
c_array.append(c)
a = A(
some_data=_some_data,
b=b,
c=c
)
a_array.append(property)
B.objects.bulk_create(b_array)
C.objects.bulk_create(c_array)
A.objects.bulk_create(a_array)
References:
Use COPY FROM command in PostgreSQL to insert in multiple tables
Postgres: \copy syntax
Create multiple tables using single .sql script file
https://www.sqlshack.com/different-approaches-to-sql-join-multiple-tables/
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 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
Problem.
After successful data migration from csv files to django /Postgres application .
When I try to add a new record via the application interface getting - duplicate key value violates unique constraint.(Since i had id's in my csv files -i use them as keys )
Basically the app try to generate id's that already migrated.
After each attempt ID increments by one so if I have 160 record I have to get this error 160 times and then when I try 160 times the time 161 record saves ok.
Any ideas how to solve it?
PostgreSQL doesn't have an actual AUTO_INCREMENT column, at least not in the way that MySQL does. Instead it has a special SERIAL. This creates a four-byte INT column and attaches a trigger to it. Behind the scenes, if PostgreSQL sees that there is no value in that ID column, it checks the value of a sequence created when that column was created.
You can see this by:
SELECT
TABLE_NAME, COLUMN_NAME, COLUMN_DEFAULT
FROM
INFORMATION_SCHEMA.COLUMNS
WHERE
TABLE_NAME='<your-table>' AND COLUMN_NAME = '<your-id-column>';
You should see something like:
table_name | column_name | column_default
--------------+---------------------------+-------------------------------------
<your-table> | <your-id-column> | nextval('<table-name>_<your-id-column>_seq'::regclass)
(1 row)
To resolve your particular issue, you're going to need to reset the value of the sequence (named <table-name>_<your-id-column>_seq) to reflect the current index.
ALTER SEQUENCE your_name_your_id_column_seq RESTART WITH 161;
Credit where credit is due.
Sequence syntax is here.
Finding the name is here.