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).
Related
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
How do you query table names and row counts for all tables in a schema using HP NonStop SQL/MX?
Thanks!
This might help you, althought this is more standard SQL and im not sure how much variation comes into sqlmx
SELECT
TableName = t.NAME,
TableSchema = s.Name,
RowCounts = p.rows
FROM
sys.tables t
INNER JOIN
sys.schemas s ON t.schema_id = s.schema_id
INNER JOIN
sys.indexes i ON t.OBJECT_ID = i.object_id
INNER JOIN
sys.partitions p ON i.object_id = p.OBJECT_ID AND i.index_id = p.index_id
WHERE
t.is_ms_shipped = 0
GROUP BY
t.NAME, s.Name, p.Rows
ORDER BY
s.Name, t.Name
Obviously this is an example, replace example data and table info with yours
Here is how to list the tables in a sql/mx schema, note that the system catalog name given here is an example, replace NONSTOP_SQLMX_SYSNAME with NONSTOP_SQLMX_xxxx where xxxx is the Expand node name of your system.
Also the definition schema name includes the schema version number, this example uses 3600. This example lists all the base table names in schema JDFCAT.T.
See chapter 10 of the SQL/MX reference manual for information on the metadata tables.
The table row counts are not stored in the system metadata, so you can't get them from there. For a table do SELECT ROW COUNT FROM TABLE;
SELECT
O.OBJECT_NAME
FROM
NONSTOP_SQLMX_SYSNAME.SYSTEM_SCHEMA.CATSYS C
INNER JOIN NONSTOP_SQLMX_SYSNAME.SYSTEM_SCHEMA.SCHEMATA S
ON (S.CAT_UID = C.CAT_UID)
INNER JOIN JDFCAT.DEFINITION_SCHEMA_VERSION_3600.OBJECTS O
on S.SCHEMA_UID = o.SCHEMA_UID
WHERE C.CAT_NAME = 'JDFCAT' AND
S.SCHEMA_NAME = 'T' AND
O.OBJECT_TYPE = 'BT'
READ UNCOMMITTED ACCESS;
I've a table "City" with more than 100k records.
The field "name" contains strings like "Roma", "La Valletta".
I receive a file with the city name, all in upper case as in "ROMA".
I need to get the id of the record that contains "Roma" when I search for "ROMA".
In SQL, I must do something like:
select id from city where upper(name) = upper(%name%)
How can I do this in kettle?
Note: if the city is not found, I use an Insert/update field to create it, so I must avoid duplicates generated by case-sensitive names.
You can make use of the String Operations steps in Pentaho Kettle. Set the Lower/Upper option to Y
Pass the city (name) from the City table to the String operations steps which will do the Upper case of your data stream i.e. city name. Join/lookup with the received file and get the required id.
More on String Operations step in pentaho wiki.
You can use a 'Database join' step. Here you can write the sql:
select id from city where upper(name) = upper(?)
and specify the city field name from the text file as parameter. With 'Number of rows to return' and 'Outer join?' you can control the join behaviour.
This solution doesn't work well with a large number of rows, as it will execute one query per row. In those cases Rishu's solution is better.
This is how I did:
First "Modified JavaScript value" step for create a query:
var queryDest="select coalesce( (select id as idcity from city where upper(name) = upper('"+replace(mycity,"'","\'\'")+"') and upper(cap) = upper('"+mycap+"') ), 0) as idcitydest";
Then I use this string as a query in a Dynamic SQL row.
After that,
IF idcitydest == 0 then
insert new city;
else
use the found record
This system make a query for file's row but it use few memory cache
I have 2 tables with information in them. I need to update the SelfServiceUserName column in table A_CLIENT with the value from the SubstVarValue column of the A_DEV_SUBSTVAR_VALUE table when the ClientUID and DeviceID match and the SubstVarName from the A_DEV_SUBSTVAR_VALUE table = samaccount name. Here is the query I've tried to run but I keep getting errors:
UPDATE A_CLIENT
SET SelfServiceUserName = (SELECT SubstVarValue
FROM A_DEV_SUBSTVAR_VALUE
WHERE A_DEV_SUBSTVAR_VALUE.SubstVarName = 'samaccountname')
WHERE A_CLIENT.ClientUID = A_DEV_SUBSTVAR_VALUE.DeviceID
I always write a join between the two tables first to get the rows I want side by side and make sure I have the JOIN clause correct.
SELECT p.ProductID, p.ProductName, p.Price AS OldPrice, n.Price as NewPrice
FROM Products as p
JOIN NewPrices as n on p.ProductID = n.ProductID
Once I have done that it's easy to change it into an update statement by replacing the SELECT clause with an UPDATE and SET:
UPDATE p
SET Price = n.Price
FROM Products as p
JOIN NewPrices as n on p.ProductID = n.ProductID
Note you don't alias the Price on the left side of the SET clause, because it is necessarily from the p (Product) table, so there is no ambiguity. You must still alias the Price on the right of the equals because it could be the field coming from either the p (Product) or n (NewPrice) table.
You could also use a CTE (Common Table Expression) if your SQL engine supports it:
WITH x AS (
SELECT p.ProductID, p.ProductName, p.Price AS OldPrice, n.Price as NewPrice
FROM Products as p
JOIN NewPrices as n on p.ProductID = n.ProductID
)
UPDATE x set OldPrice = NewPrice
Try something like
update a_client c
inner join a_dev_substvar_value d on
c.clientuid = d.deviceid
set
c.selfserviceusername = d.substvarvalue
where
d.substvarname = 'samaccountname';
Note, you should try avoid writing select statements in your were clause because it is run for ever row returned. This can be a big performance hit.
That should work.
I have two tables I would like to call, but I am not sure if it is possible to combine them into one query or I have to some how call 2 different queries.
Basically I have 2 tables:
1) item_table: name/id etc. + category ID
2) category_table: categoryID, categoryName, categoryParentID.
The parent categories are also inside the same table with their own name.
I would like to call on my details from item_table, as well as getting the name of the category, as well as the NAME of the parent category.
I know how to get the item_table data, plus the categoryName through an INNER JOIN. But can I use the same query to get the categoryParent's name?
If not, what would be the mist efficient way to do it? The rest of the code is in C++.
SELECT item_table.item_name, c1.name AS CatName, c2.name AS ParentCatName
FROM item_table join category_table c1 on item_table.categoryID=c1.categoryID
LEFT OUTER JOIN category_table c2 ON c2.categoryID = c1.categoryParentID
SQL Fiddle: here