Transactions with Prepared Statements fails - sqlite

I try to use transactions with prepared statementsin order to update table INVENTORY where :
CREATE TABLE "INVENTORY" (
"product" VARCHAR NOT NULL,
"version" VARCHAR NOT NULL,
"lot" VARCHAR,
"barcode" VARCHAR,
"quantity" INTEGER,
PRIMARY KEY ("barcode")
);
What I want to do is to insert a new row, but if in my table a row exists with the same primary key then to update it by adding the old value + the new.
I read this and this and I think I followed the instructions right.
String sqInsert = "INSERT INTO INVENTORY VALUES ('100541026044','01','301610101','10054102604401301610101','5000')";
String sqUpdate = "UPDATE INVENTORY set quantity = quantity + 5000 where barcode='10054102604401301610101'";
// transaction block start
c.setAutoCommit(false);
stm = c.prepareStatement(sqInsert);
System.out.println("try to insert");
result = stm.executeUpdate();
System.out.println("try to update");
stm = c.prepareStatement(sqUpdate);
result = stm.executeUpdate();
c.commit(); //transaction block end
System.out.println("Done!");
In my table a row with barcode=10054102604401301610101 exists, so I want the update to be executed. However, I get
try to insert
Error inserting products :[SQLITE_CONSTRAINT] Abort due to constraint violation (UNIQUE constraint failed: INVENTORY.barcode)
Note: (I don't set the values from query, but with stm.setString(1, "string");) I just want to be short the code here

Of course it will fail due to a duplicated primary key on the bar code.
First do the update
stm = c.prepareStatement(sqUpdate);
result = stm.executeUpdate();
Then check the value of result which will be the number of rows affected by the update. If it is zero then the product with given barcode didn't exist so after the update do
if (0==result) {
stm = c.prepareStatement(sqInsert);
stm.executeUpdate();
}
You'll want to put everything under a try {} catch {} to avoid a resource leak or leaving the connection unusable
try {
c.setAutoCommit(false);
stm = c.prepareStatement(sqUpdate);
result = stm.executeUpdate();
if (0==result) {
stm.close();
stm = null;
stm = c.prepareStatement(sqInsert);
stm.executeUpdate();
stm.close();
stm = null;
}
c.commit();
} catch (SQLException e) {
if (stm!=null) stm.close();
c.rollback();
}

Related

Can SQLite return the id when inserting data?

I'm using sqlite3.exe to execute queries against my DB, using the following code.
public static string QueryDB(string query)
{
string output = System.String.Empty;
string error = System.String.Empty;
System.Diagnostics.ProcessStartInfo startInfo = new System.Diagnostics.ProcessStartInfo();
startInfo.FileName = "C:\\sqlite\\sqlite3.exe";
startInfo.Arguments = "test.db " + query;
startInfo.UseShellExecute = false;
startInfo.CreateNoWindow = true;
startInfo.RedirectStandardError = true;
startInfo.RedirectStandardOutput = true;
startInfo.WindowStyle = System.Diagnostics.ProcessWindowStyle.Hidden;
try
{
using(System.Diagnostics.Process sqlite3 = System.Diagnostics.Process.Start(startInfo))
{
output = sqlite3.StandardOutput.ReadToEnd();
error = sqlite3.StandardError.ReadToEnd();
sqlite3.WaitForExit();
}
}
catch (System.Exception ex)
{
System.Console.WriteLine(ex.ToString());
return null;
}
return output;
}
I'm inserting data into a table, and I'd like it to return the id of the inserted data. Is there a way to get SQLite to do this?
For example, my query might look like this "INSERT INTO mytable (some_values) VALUES ('some value');". After this query is run, I'd like output to contain the rowid of the inserted data. Is there any way to do this (a command line switch, etc.)?
A possible workaround, is to run two commands against the DB. First insert the data, then get the last inserted row id. In which case, the query would look like this "\"INSERT INTO mytable (some_values) VALUES ('some value'); SELECT last_insert_rowid();\""
You should not use max(id) or similar function in DB.
In this specific case it can work, under the condition that you use ONE connection and ONE thread to write data to DB.
In case of multiple connections you can get wrong answer.
From version SQLite 3.35.0 it supports returning close in the insert statement (SQLite Returning Close)
create table test (
id integer not null primary key autoincrement,
val text
);
insert into table test(val) values (val) returning id;
Would you consider this:
select max(id) from your_table_name;
or embedded function last_insert_rowid()?

get all data from dynamo db table without supplying any PK

I am trying to fetch all the data from my dynamodb table but unable to get as all the methods for Query / Scan operates with input parameter. so i tried getting all the rows which having primary key greater than 0.
var table = Table.LoadTable(client,Utilities.Utility.EmployeeTable);
ScanFilter filter = new ScanFilter();
filter.AddCondition("iemp_id", ScanOperator.GreaterThan, 0);
ScanOperationConfig config = new ScanOperationConfig()
{
Filter = filter,
// Optional parameters.
Select = SelectValues.SpecificAttributes,
AttributesToGet = new List<string> { "iemp_id", "demp_salary", "semp_name" }
//ConsistentRead = true
};
Search search = table.Scan(config);`
Here i am getting search.Matches = 0 where it should return data from my table.
You have only two options
1.Query : You need to supply Partition Key(mandatory) and optionally Range key.
2.Scan: Full scan of the table with out Partition key/Range Key.
In your case you will have to do full scan of the table.
DynamoDBQScanExpression scanExpression = new DynamoDBScanExpression();
scanExpression .withFilterExpression(filterexpression)
.withExpressionAttributeValues(expression values);

Insert the newset value in a table and drop the old ones

I have a method which saves somes records for a machine in a table. However, I may insert by accident multiple times the records for the same machine in a day, so I want for this day to save the newest insert and drop the old ones. I thought one solution:
String sq = "SELECT date, idMachine "
+ "FROM MACHINES_RECORDS WHERE date = ? AND idMachine = ?";
try {
Class.forName(typeDB);
c = DriverManager.getConnection(path);
stm = c.prepareStatement(sq);
ResultSet rs = stm.executeQuery();
if (rs.next()) {
do {
//call an another method to drop this value
} while(rs.next());
}else {
//call an another method to insert this value
}
}catch (SQLException e) {
System.out.println(e.getMessage());
} finally {
if (stm != null)
stm.close();
if (c != null)
c.close();
}
Is there any better/smartest solution from this, so I can make all theses actions in the same method?
With a unique index (possibly the primary key) on date and idmachine you would use INSERT ... ON DUPLICATE KEY UPDATE, so as to insert when there is no entry for that machine on that day or update the existing record with the new data otherwise.
insert into machines_records
(machineid, date, data)
values
(#id, #date, #data)
on duplicate key update data = #data;
EDIT: I see you removed the MySQL tag. So you want an answer for SQLite. In SQLite you'd use INSERT OR REPLACE:
insert or replace into machines_records
(machineid, date, data)
values
(#id, #date, #data);

Why can SQLite not add up DECIMAL values?

sqlite> create table test (Qty DECIMAL(10,2));
sqlite> insert into test values(1059.79);
sqlite> insert into test values(-1050);
sqlite> insert into test values(83.58);
sqlite> insert into test values(130.51);
sqlite> insert into test values(-5);
sqlite> insert into test values(-136.68);
sqlite> insert into test values(-2.6);
sqlite> insert into test values(-75);
sqlite> insert into test values(-4.6);
sqlite> select sum(Qty) FROM TEST;
-6.21724893790088e-14
Given that I explicitly specified DECIMAL(10,2) as the field type, why is the sum not 0?
SQLite does not have a DECIMAL type. Math is performed using 64-bit floating point values.
See SQLite3 data types
Rather than messing about, and making my sql incompatible with the other databases I support, I merely wrote a user-defined replacement for the SQLite SUM function, like so:
[SqliteFunctionAttribute(Name = "SUM", Arguments = 1, FuncType = FunctionType.Aggregate)]
class SqliteSum : SqliteFunction {
public override void Step(object[] args, int stepNumber, ref object contextData) {
if (args.Length < 1 || args[0] == null || args[0] == DBNull.Value)
return;
try {
decimal d = Math.Round(Convert.ToDecimal(args[0]), 4);
if (contextData != null) d += (Decimal)contextData;
contextData = d;
} catch (Exception ex) {
WebServer.Log("Exception: {0}", ex);
}
}
public override object Final(object contextData) {
return contextData;
}
}
SQLite does not have decimal type :
NULL
INTEGER
REAL
TEXT
BLOB
So maybe it is converted to Text , then suming happens.
SQLite is powerfull enough to work with, and can rely on for calculations and math, too.

How do I check in SQLite whether a table exists?

How do I, reliably, check in SQLite, whether a particular user table exists?
I am not asking for unreliable ways like checking if a "select *" on the table returned an error or not (is this even a good idea?).
The reason is like this:
In my program, I need to create and then populate some tables if they do not exist already.
If they do already exist, I need to update some tables.
Should I take some other path instead to signal that the tables in question have already been created - say for example, by creating/putting/setting a certain flag in my program initialization/settings file on disk or something?
Or does my approach make sense?
I missed that FAQ entry.
Anyway, for future reference, the complete query is:
SELECT name FROM sqlite_master WHERE type='table' AND name='{table_name}';
Where {table_name} is the name of the table to check.
Documentation section for reference: Database File Format. 2.6. Storage Of The SQL Database Schema
This will return a list of tables with the name specified; that is, the cursor will have a count of 0 (does not exist) or a count of 1 (does exist)
If you're using SQLite version 3.3+ you can easily create a table with:
create table if not exists TableName (col1 typ1, ..., colN typN)
In the same way, you can remove a table only if it exists by using:
drop table if exists TableName
A variation would be to use SELECT COUNT(*) instead of SELECT NAME, i.e.
SELECT count(*) FROM sqlite_master WHERE type='table' AND name='table_name';
This will return 0, if the table doesn't exist, 1 if it does. This is probably useful in your programming since a numerical result is quicker / easier to process. The following illustrates how you would do this in Android using SQLiteDatabase, Cursor, rawQuery with parameters.
boolean tableExists(SQLiteDatabase db, String tableName)
{
if (tableName == null || db == null || !db.isOpen())
{
return false;
}
Cursor cursor = db.rawQuery(
"SELECT COUNT(*) FROM sqlite_master WHERE type = ? AND name = ?",
new String[] {"table", tableName}
);
if (!cursor.moveToFirst())
{
cursor.close();
return false;
}
int count = cursor.getInt(0);
cursor.close();
return count > 0;
}
You could try:
SELECT name FROM sqlite_master WHERE name='table_name'
See (7) How do I list all tables/indices contained in an SQLite database in the SQLite FAQ:
SELECT name FROM sqlite_master
WHERE type='table'
ORDER BY name;
Use:
PRAGMA table_info(your_table_name)
If the resulting table is empty then your_table_name doesn't exist.
Documentation:
PRAGMA schema.table_info(table-name);
This pragma returns one row for each column in the named table. Columns in the result set include the column name, data type, whether or not the column can be NULL, and the default value for the column. The "pk" column in the result set is zero for columns that are not part of the primary key, and is the index of the column in the primary key for columns that are part of the primary key.
The table named in the table_info pragma can also be a view.
Example output:
cid|name|type|notnull|dflt_value|pk
0|id|INTEGER|0||1
1|json|JSON|0||0
2|name|TEXT|0||0
SQLite table names are case insensitive, but comparison is case sensitive by default. To make this work properly in all cases you need to add COLLATE NOCASE.
SELECT name FROM sqlite_master WHERE type='table' AND name='table_name' COLLATE NOCASE
If you are getting a "table already exists" error, make changes in the SQL string as below:
CREATE table IF NOT EXISTS table_name (para1,para2);
This way you can avoid the exceptions.
If you're using fmdb, I think you can just import FMDatabaseAdditions and use the bool function:
[yourfmdbDatabase tableExists:tableName].
The following code returns 1 if the table exists or 0 if the table does not exist.
SELECT CASE WHEN tbl_name = "name" THEN 1 ELSE 0 END FROM sqlite_master WHERE tbl_name = "name" AND type = "table"
Note that to check whether a table exists in the TEMP database, you must use sqlite_temp_master instead of sqlite_master:
SELECT name FROM sqlite_temp_master WHERE type='table' AND name='table_name';
Here's the function that I used:
Given an SQLDatabase Object = db
public boolean exists(String table) {
try {
db.query("SELECT * FROM " + table);
return true;
} catch (SQLException e) {
return false;
}
}
Use this code:
SELECT name FROM sqlite_master WHERE type='table' AND name='yourTableName';
If the returned array count is equal to 1 it means the table exists. Otherwise it does not exist.
class CPhoenixDatabase():
def __init__(self, dbname):
self.dbname = dbname
self.conn = sqlite3.connect(dbname)
def is_table(self, table_name):
""" This method seems to be working now"""
query = "SELECT name from sqlite_master WHERE type='table' AND name='{" + table_name + "}';"
cursor = self.conn.execute(query)
result = cursor.fetchone()
if result == None:
return False
else:
return True
Note: This is working now on my Mac with Python 3.7.1
You can write the following query to check the table existance.
SELECT name FROM sqlite_master WHERE name='table_name'
Here 'table_name' is your table name what you created. For example
CREATE TABLE IF NOT EXISTS country(country_id INTEGER PRIMARY KEY AUTOINCREMENT, country_code TEXT, country_name TEXT)"
and check
SELECT name FROM sqlite_master WHERE name='country'
Use
SELECT 1 FROM table LIMIT 1;
to prevent all records from being read.
Using a simple SELECT query is - in my opinion - quite reliable. Most of all it can check table existence in many different database types (SQLite / MySQL).
SELECT 1 FROM table;
It makes sense when you can use other reliable mechanism for determining if the query succeeded (for example, you query a database via QSqlQuery in Qt).
The most reliable way I have found in C# right now, using the latest sqlite-net-pcl nuget package (1.5.231) which is using SQLite 3, is as follows:
var result = database.GetTableInfo(tableName);
if ((result == null) || (result.Count == 0))
{
database.CreateTable<T>(CreateFlags.AllImplicit);
}
The function dbExistsTable() from R DBI package simplifies this problem for R programmers. See the example below:
library(DBI)
con <- dbConnect(RSQLite::SQLite(), ":memory:")
# let us check if table iris exists in the database
dbExistsTable(con, "iris")
### returns FALSE
# now let us create the table iris below,
dbCreateTable(con, "iris", iris)
# Again let us check if the table iris exists in the database,
dbExistsTable(con, "iris")
### returns TRUE
I thought I'd put my 2 cents to this discussion, even if it's rather old one..
This query returns scalar 1 if the table exists and 0 otherwise.
select
case when exists
(select 1 from sqlite_master WHERE type='table' and name = 'your_table')
then 1
else 0
end as TableExists
My preferred approach:
SELECT "name" FROM pragma_table_info("table_name") LIMIT 1;
If you get a row result, the table exists. This is better (for me) then checking with sqlite_master, as it will also check attached and temp databases.
This is my code for SQLite Cordova:
get_columnNames('LastUpdate', function (data) {
if (data.length > 0) { // In data you also have columnNames
console.log("Table full");
}
else {
console.log("Table empty");
}
});
And the other one:
function get_columnNames(tableName, callback) {
myDb.transaction(function (transaction) {
var query_exec = "SELECT name, sql FROM sqlite_master WHERE type='table' AND name ='" + tableName + "'";
transaction.executeSql(query_exec, [], function (tx, results) {
var columnNames = [];
var len = results.rows.length;
if (len>0){
var columnParts = results.rows.item(0).sql.replace(/^[^\(]+\(([^\)]+)\)/g, '$1').split(','); ///// RegEx
for (i in columnParts) {
if (typeof columnParts[i] === 'string')
columnNames.push(columnParts[i].split(" ")[0]);
};
callback(columnNames);
}
else callback(columnNames);
});
});
}
Table exists or not in database in swift
func tableExists(_ tableName:String) -> Bool {
sqlStatement = "SELECT name FROM sqlite_master WHERE type='table' AND name='\(tableName)'"
if sqlite3_prepare_v2(database, sqlStatement,-1, &compiledStatement, nil) == SQLITE_OK {
if sqlite3_step(compiledStatement) == SQLITE_ROW {
return true
}
else {
return false
}
}
else {
return false
}
sqlite3_finalize(compiledStatement)
}
c++ function checks db and all attached databases for existance of table and (optionally) column.
bool exists(sqlite3 *db, string tbl, string col="1")
{
sqlite3_stmt *stmt;
bool b = sqlite3_prepare_v2(db, ("select "+col+" from "+tbl).c_str(),
-1, &stmt, 0) == SQLITE_OK;
sqlite3_finalize(stmt);
return b;
}
Edit: Recently discovered the sqlite3_table_column_metadata function. Hence
bool exists(sqlite3* db,const char *tbl,const char *col=0)
{return sqlite3_table_column_metadata(db,0,tbl,col,0,0,0,0,0)==SQLITE_OK;}
You can also use db metadata to check if the table exists.
DatabaseMetaData md = connection.getMetaData();
ResultSet resultSet = md.getTables(null, null, tableName, null);
if (resultSet.next()) {
return true;
}
If you are running it with the python file and using sqlite3 obviously. Open command prompt or bash whatever you are using use
python3 file_name.py first in which your sql code is written.
Then Run sqlite3 file_name.db.
.table this command will give tables if they exist.
I wanted to add on Diego VĂ©lez answer regarding the PRAGMA statement.
From https://sqlite.org/pragma.html we get some useful functions that can can return information about our database.
Here I quote the following:
For example, information about the columns in an index can be read using the index_info pragma as follows:
PRAGMA index_info('idx52');
Or, the same content can be read using:
SELECT * FROM pragma_index_info('idx52');
The advantage of the table-valued function format is that the query can return just a subset of the PRAGMA columns, can include a WHERE clause, can use aggregate functions, and the table-valued function can be just one of several data sources in a join...
Diego's answer gave PRAGMA table_info(table_name) like an option, but this won't be of much use in your other queries.
So, to answer the OPs question and to improve Diegos answer, you can do
SELECT * FROM pragma_table_info('table_name');
or even better,
SELECT name FROM pragma_table_list('table_name');
if you want to mimic PoorLuzers top-voted answer.
If you deal with Big Table, I made a simple hack with Python and Sqlite and you can make the similar idea with any other language
Step 1: Don't use (if not exists) in your create table command
you may know that this if you run this command that will have an exception if you already created the table before, and want to create it again, but this will lead us to the 2nd step.
Step 2: use try and except (or try and catch for other languages) to handle the last exception
here if you didn't create the table before, the try case will continue, but if you already did, you can put do your process at except case and you will know that you already created the table.
Here is the code:
def create_table():
con = sqlite3.connect("lists.db")
cur = con.cursor()
try:
cur.execute('''CREATE TABLE UNSELECTED(
ID INTEGER PRIMARY KEY)''')
print('the table is created Now')
except sqlite3.OperationalError:
print('you already created the table before')
con.commit()
cur.close()
You can use a simple way, i use this method in C# and Xamarin,
public class LoginService : ILoginService
{
private SQLiteConnection dbconn;
}
in login service class, i have many methods for acces to the data in sqlite, i stored the data into a table, and the login page
it only shows when the user is not logged in.
for this purpose I only need to know if the table exists, in this case if it exists it is because it has data
public int ExisteSesion()
{
var rs = dbconn.GetTableInfo("Sesion");
return rs.Count;
}
if the table does not exist, it only returns a 0, if the table exists it is because it has data and it returns the total number of rows it has.
In the model I have specified the name that the table must receive to ensure its correct operation.
[Table("Sesion")]
public class Sesion
{
[PrimaryKey]
public int Id { get; set; }
public string Token { get; set; }
public string Usuario { get; set; }
}
Look into the "try - throw - catch" construct in C++. Most other programming languages have a similar construct for handling errors.

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