Related
I create multiple tables (at least two):
CREATE TABLE prices0
(
dt NOT NULL PRIMARY KEY,
buy REAL NOT NULL,
sell REAL NOT NULL
) WITHOUT ROWID;
CREATE TABLE prices1
(
dt NOT NULL PRIMARY KEY,
buy REAL NOT NULL,
sell REAL NOT NULL
) WITHOUT ROWID;
and insert statements:
INSERT INTO prices0 (dt, buy, sell) VALUES (?, ?, ?);
INSERT INTO prices0 (dt, buy, sell) VALUES (?, ?, ?);
In my C++ code I open and execute the statements as follows:
for (size_t i = 0; i < 2; ++i)
{
sqlite3_prepare(...);
}
for (size_t i = 0; i < 2; ++i)
{
sqlite3_bind_int64(...);
sqlite3_bind_double(...);
sqlite3_bind_double(...);
sqlite3_step(...);
sqlite3_reset(...);
}
The first call of sqlite3_step function fails with error code '1' and the message 'SQL logic error'.
The same code does not produce any errors with the single table.
it is because when I create the second table the database schema is changed, see
p->zErrMsg = sqlite3DbStrDup(db, "database schema has changed");
in SQLite sources.
With SQLite and Cordova on an Android device.
I have a database containing a table with some fields.
None of the fields is a primary key so the records have a default rowid generated by SQLite.
Here is a screenshot of the table in Chrome debugger:
I'm trying to access that rowid (I spare you all the database code and focus on the query):
tx.executeSql('SELECT * FROM ServicesRondes', [], function(tx, res) {
console.log(res.rows.length); // shows 5
if (res.rows.length > 0) {
for(var i = 0; i < res.rows.length; i++) {
console.log(res.rows.item(i).time); // shows the time record
console.log(res.rows.item(i).rowid); // shows undefined
}
}
}
So the problem is that the rowid is undefined in the logs.
I've found only one link with a guy answering his own question: https://forum.qt.io/topic/53217/solved-how-to-access-sqlite-rowid
As you can see, he made a query with rowid to solve his problem.
But it's not really what I want (I want to select all) and furthermore, I don't get why it works this way and not the other way.
Of course I could create my own autoincremented primary key field but I'd like to avoid it and this is not my question.
SELECT * returns all columns that you have declared in the table definition.
If you want the rowid column to show up with *, you have to include it there:
CREATE TABLE ServicesRondes (
rowid INTEGER PRIMARY KEY,
userUuid UUID,
secteurId UUID,
time TIMESTAMP,
[...]
);
I have SQL Server database and I want to change the identity column because it started
with a big number 10010 and it's related with another table, now I have 200 records and I want to fix this issue before the records increases.
What's the best way to change or reset this column?
You can not update identity column.
SQL Server does not allow to update the identity column unlike what you can do with other columns with an update statement.
Although there are some alternatives to achieve a similar kind of requirement.
When Identity column value needs to be updated for new records
Use DBCC CHECKIDENT which checks the current identity value for the table and if it's needed, changes the identity value.
DBCC CHECKIDENT('tableName', RESEED, NEW_RESEED_VALUE)
When Identity column value needs to be updated for existing records
Use IDENTITY_INSERT which allows explicit values to be inserted into the identity column of a table.
SET IDENTITY_INSERT YourTable {ON|OFF}
Example:
-- Set Identity insert on so that value can be inserted into this column
SET IDENTITY_INSERT YourTable ON
GO
-- Insert the record which you want to update with new value in the identity column
INSERT INTO YourTable(IdentityCol, otherCol) VALUES(13,'myValue')
GO
-- Delete the old row of which you have inserted a copy (above) (make sure about FK's)
DELETE FROM YourTable WHERE ID=3
GO
--Now set the idenetity_insert OFF to back to the previous track
SET IDENTITY_INSERT YourTable OFF
If got your question right you want to do something like
update table
set identity_column_name = some value
Let me tell you, it is not an easy process and it is not advisable to use it, as there may be some foreign key associated on it.
But here are steps to do it, Please take a back-up of table
Step 1- Select design view of the table
Step 2- Turn off the identity column
Now you can use the update query.
Now redo the step 1 and step 2 and Turn on the identity column
Reference
You need to
set identity_insert YourTable ON
Then delete your row and reinsert it with different identity.
Once you have done the insert don't forget to turn identity_insert off
set identity_insert YourTable OFF
--before running this make sure Foreign key constraints have been removed that reference the ID.
--set table to allow identity to be inserted
SET IDENTITY_INSERT yourTable ON;
GO
--insert everything into a temp table
SELECT *
INTO #tmpYourTable
FROM yourTable
--clear your table
DELETE FROM yourTable
--insert back all the values with the updated ID column
INSERT INTO yourTable (IDCol, OtherCols)
SELECT ID+1 as updatedID --put any other update logic to the ID here
, OtherCols FROM #tmpYourTable
--drop the temp table
DROP TABLE #tmpYourTable
--put identity back to normal
SET IDENTITY_INSERT yourTable OFF;
GO
Try using DBCC CHECKIDENT:
DBCC CHECKIDENT ('YourTable', RESEED, 1);
SET IDENTITY_INSERT dbo.TableName ON
INSERT INTO dbo.TableName
(
TableId, ColumnName1, ColumnName2, ColumnName3
)
VALUES
(
TableId_Value, ColumnName1_Value, ColumnName2_Value, ColumnName3_Value
)
SET IDENTITY_INSERT dbo.TableName OFF
When using Identity_Insert don't forget to include the column names because sql will not allow you to insert without specifying them
DBCC CHECKIDENT(table_name, RESEED, value)
table_name = give the table you want to reset value
value=initial value to be zero,to start identity column with 1
copy your table to a new table without identity column.
select columns into newtable from yourtable
add an identity column to newtable with new seed and make it as a primary key
ALTER TABLE tableName ADD id MEDIUMINT NOT NULL AUTO_INCREMENT KEY
You can also use SET IDENTITY INSERT to allow you to insert values into an identity column.
Example:
SET IDENTITY_INSERT dbo.Tool ON
GO
And then you can insert into an identity column the values you need.
I had similar problem I needed update some IDs what I did was ( i needed to Increase them by 10k ):
set identity_insert YourTable ON
INSERT INTO YourTable
([ID]
,[something1]
,[something2]
,[something3])
SELECT
([ID] + 10000)
,[something1]
,[something2]
,[something3])
FROM YourTable
WHERE something1 = 'needs updeted id'
AND something2 = 'some other condition'
set identity_insert YourTable OFF
DELETE FROM YourTable
WHERE ID >= 'your old ID From'
AND ID <= 'Your old ID To'
And that's it. Hope you understand this logic, in my case there was also PK-FK keys connection with other tables, which meant i had to update them, before i could delete from 'YourTable' original rows.
I know there is already answers to this I just wanted to leave SQL query as example,
ALTER TABLE tablename add newcolumn int
update tablename set newcolumn=existingcolumnname
ALTER TABLE tablename DROP COLUMN existingcolumnname;
EXEC sp_RENAME 'tablename.oldcolumn' , 'newcolumnname', 'COLUMN'
update tablename set newcolumnname=value where condition
However above code works only if there is no primary-foreign key relation
Complete solution for C# programmers using command builder
First of all, you have to know this facts:
In any case, you cannot modify an identity column, so you have to delete the row and re-add with new identity.
You cannot remove the identity property from the column (you would have to remove to column)
The custom command builder from .net always skips the identity column, so you cannot use it for this purpose.
So, once knowing that, what you have to do is. Either program your own SQL Insert statement, or program you own insert command builder. Or use this one that I'be programmed for you. Given a DataTable, generates the SQL Insert script:
public static string BuildInsertSQLText ( DataTable table )
{
StringBuilder sql = new StringBuilder(1000,5000000);
StringBuilder values = new StringBuilder ( "VALUES (" );
bool bFirst = true;
bool bIdentity = false;
string identityType = null;
foreach(DataRow myRow in table.Rows)
{
sql.Append( "\r\nINSERT INTO " + table.TableName + " (" );
foreach ( DataColumn column in table.Columns )
{
if ( column.AutoIncrement )
{
bIdentity = true;
switch ( column.DataType.Name )
{
case "Int16":
identityType = "smallint";
break;
case "SByte":
identityType = "tinyint";
break;
case "Int64":
identityType = "bigint";
break;
case "Decimal":
identityType = "decimal";
break;
default:
identityType = "int";
break;
}
}
else
{
if ( bFirst )
bFirst = false;
else
{
sql.Append ( ", " );
values.Append ( ", " );
}
sql.Append ("[");
sql.Append ( column.ColumnName );
sql.Append ("]");
//values.Append (myRow[column.ColumnName].ToString() );
if (myRow[column.ColumnName].ToString() == "True")
values.Append("1");
else if (myRow[column.ColumnName].ToString() == "False")
values.Append("0");
else if(myRow[column.ColumnName] == System.DBNull.Value)
values.Append ("NULL");
else if(column.DataType.ToString().Equals("System.String"))
{
values.Append("'"+myRow[column.ColumnName].ToString()+"'");
}
else
values.Append (myRow[column.ColumnName].ToString());
//values.Append (column.DataType.ToString() );
}
}
sql.Append ( ") " );
sql.Append ( values.ToString () );
sql.Append ( ")" );
if ( bIdentity )
{
sql.Append ( "; SELECT CAST(scope_identity() AS " );
sql.Append ( identityType );
sql.Append ( ")" );
}
bFirst = true;
sql.Append(";");
values = new StringBuilder ( "VALUES (" );
} //fin foreach
return sql.ToString ();
}
There's a few ways to do this as I've seen., but the best and faster way in my opinion is the following one:
The identity columns have a counter that isn't necessarily the same as the columns registered, you can see the value of this counter with the folowing SQL command:
DBCC CHECKIDENT('tableName', NORESEED);
Then, if you want to edit the identity column you will not be able, but I recommend to make a new register after reseeding the counter to the number you need. To reseed the counter use this command:
DBCC CHECKIDENT('tableName', RESEED, desiredNumber);
I have solved this problem firstly using DBCC and then using insert. For example if your table is
Firstly set new current ID Value on the table as NEW_RESEED_VALUE
MyTable {
IDCol,
colA,
colB
}
DBCC CHECKIDENT('MyTable', RESEED, NEW_RESEED_VALUE)
then you can use
insert into MyTable (colA, ColB) select colA, colB from MyTable
This would duplicate all your records but using new IDCol value starting as NEW_RESEED_VALUE. You can then remove higher ID Value duplicate rows once your have removed/moved their foreign key references, if any.
You can create a new table using the following code.
SELECT IDENTITY (int, 1, 1) AS id, column1, column2
INTO dbo.NewTable
FROM dbo.OldTable
Then delete the old db, and rename the new db to the old db's name. Note: that column1 and column2 represent all the columns in your old table that you want to keep in your new table.
I did the following:
MOVE related data into temporary storage
UPDATE primary key/identity column value (dropping and creating constraints)
RE-INSERT related data with new foreign key value
I wrapped my solution in a STORED PROCEDURE:
CREATE PROCEDURE [dbo].[UpdateCustomerLocationId]
#oldCustomerLocationId INT,
#newCustomerLocationId INT
AS
/*
Updates CustomerLocation.CustomerLocationId #oldCustomerLocationId to #newCustomerLocationId
Example:
EXEC [dbo].[UpdateCustomerLocationId]
#oldCustomerLocationId = 6154874,
#newCustomerLocationId = 50334;
*/
BEGIN
SET NOCOUNT ON;
-- exit if #oldCustomerLocationId does not exists
IF NOT EXISTS (SELECT * FROM dbo.CustomerLocation cl WHERE cl.CustomerLocationId = #oldCustomerLocationId)
BEGIN
PRINT CONCAT('CustomerLocationId ''', #oldCustomerLocationId, ''' (#oldCustomerLocationId) does not exist in dbo.CustomerLocation');
RETURN 1; -- 0 = success, > 0 = failure
END
-- exit if #newCustomerLocationId already exists
IF EXISTS (SELECT * FROM dbo.CustomerLocation cl WHERE cl.CustomerLocationId = #newCustomerLocationId)
BEGIN
PRINT CONCAT('CustomerLocationId ''', #newCustomerLocationId, ''' (#newCustomerLocationId) already exists in dbo.CustomerLocation');
RETURN 2; -- 0 = success, > 0 = failure
END
BEGIN TRAN;
BEGIN -- MOVE related data into temporary storage
IF EXISTS (SELECT * FROM dbo.CustomerLocationData t WHERE t.CustomerLocationId = #oldCustomerLocationId) BEGIN
IF OBJECT_ID('tempdb..#CustomerLocationData') IS NOT NULL
DROP TABLE #CustomerLocationData;
SELECT * INTO #CustomerLocationData FROM dbo.CustomerLocationData t WHERE t.CustomerLocationId = #oldCustomerLocationId;
DELETE t FROM dbo.CustomerLocationData t WHERE t.CustomerLocationId = #oldCustomerLocationId;
END
END
BEGIN -- UPDATE dbo.CustomerLocation
-- DROP CONSTRAINTs
ALTER TABLE [dbo].[CustomerLocation] DROP CONSTRAINT [UC_CustomerLocation];
-- INSERT OLD record with new CustomerLocationId
SET IDENTITY_INSERT dbo.CustomerLocation ON;
INSERT INTO dbo.CustomerLocation
(
CustomerLocationId, CustomerId, LocationId, CustomerLocationIdent, CustomerLocationIdent2, LocationIdent, LocationName, CustomerDistrictId,
CustomerLocationGUID, UpdatedOn, IssueManager, EnrollSelfMonitoring, TemperatureControlDeadlineHour, CreatedOn, OperationBegin, ActiveCustomer,
Comments, LocationName2, ParentGroup, TempString1, TempString2, TempString3, TempString4, TempString5, AutoInheritFromLocation, ClassificationPrimary
)
SELECT #newCustomerLocationId AS CustomerLocationId, CustomerId,LocationId, CustomerLocationIdent, CustomerLocationIdent2, LocationIdent, LocationName, CustomerDistrictId,
CustomerLocationGUID, UpdatedOn, IssueManager, EnrollSelfMonitoring, TemperatureControlDeadlineHour, CreatedOn, OperationBegin, ActiveCustomer,
Comments,LocationName2, ParentGroup, TempString1, TempString2, TempString3, TempString4, TempString5, AutoInheritFromLocation, ClassificationPrimary
FROM dbo.CustomerLocation
WHERE CustomerLocationId = #oldCustomerLocationId;
SET IDENTITY_INSERT dbo.CustomerLocation OFF;
-- DELETE OLD record
DELETE cl FROM dbo.CustomerLocation cl WHERE cl.CustomerLocationId = #oldCustomerLocationId;
-- ADD CONSTRAINTS
ALTER TABLE [dbo].[CustomerLocation] ADD CONSTRAINT [UC_CustomerLocation] UNIQUE NONCLUSTERED ([CustomerId], [LocationId]);
END
BEGIN -- re-INSERT related data from temporary storage
IF OBJECT_ID('tempdb..#CustomerLocationData') IS NOT NULL BEGIN
SET IDENTITY_INSERT dbo.CustomerLocationData ON;
INSERT INTO dbo.CustomerLocationData (Guid, CustomerLocationId, CustomerLocationDataTypeId, Date, Category, Data)
SELECT Guid, #newCustomerLocationId CustomerLocationId, CustomerLocationDataTypeId, Date, Category, Data FROM #CustomerLocationData;
SET IDENTITY_INSERT dbo.CustomerLocationData OFF;
END
END
COMMIT TRAN;
END
This happened to me because I did a merge that was updating the ID that I was doing the Merge on.
Example that did not work (note ClownID):
MERGE ArchitectMain.dbo.BackendClowns AS TGT
USING (
SELECT ClownID
,ClownName
,Description
,Active
,EmailSubject
,AddedBy
,Added
FROM #temptable1
) AS SRC(ClownID, ClownName, Description, Active, EmailSubject, AddedBy, Added)
ON (TGT.ClownID = SRC.ClownID)
WHEN MATCHED
THEN
UPDATE
SET ClownID = SRC.ClownID
,ClownName = SRC.ClownName
,Description = SRC.Description
,Active = SRC.Active
,EmailSubject = SRC.EmailSubject
,AddedBy = SRC.AddedBy
,Added = SRC.Added;
Example that worked (note ClownID):
MERGE ArchitectMain.dbo.BackendClowns AS TGT
USING (
SELECT ClownID
,ClownName
,Description
,Active
,EmailSubject
,AddedBy
,Added
FROM #temptable1
) AS SRC(ClownID, ClownName, Description, Active, EmailSubject, AddedBy, Added)
ON (TGT.ClownID = SRC.ClownID)
WHEN MATCHED
THEN
UPDATE
SET ClownName = SRC.ClownName
,Description = SRC.Description
,Active = SRC.Active
,EmailSubject = SRC.EmailSubject
,AddedBy = SRC.AddedBy
,Added = SRC.Added;
Update is not allowed:
but you can
INSERT new data with correct key
Delete reg
import: all fields must be declared in insert into
sample: reg 5 must be changed to 4:
set IDENTITY_INSERT Gastos_ReclamacionCausa on
insert into Gastos_ReclamacionCausa
(IDCausa,TextoCombo,Asunto,Mensaje,EsBaja)
select 4,TextoCombo,Asunto,Mensaje,EsBaja from Gastos_ReclamacionCausa where idcausa=5
delete from Gastos_ReclamacionCausa where idcausa = 5
set IDENTITY_INSERT Gastos_ReclamacionCausa off
If you specifically need to change the primary key value to a different number (ex 123 -> 1123). The identity property blocks changing a PK value. Set Identity_insert isn't going to work. Doing an Insert/Delete is not advisable if you have cascading deletes (unless you turn off referential integrity checking).
EDIT: Newer versions of SQL don't allow changing the syscolumns entity, so part of my solution has to be done the hard way. Refer to this SO on how to remove Identity from a primary key instead:
Remove Identity from a column in a table
This script will turn off identity on a PK:
***********************
sp_configure 'allow update', 1
go
reconfigure with override
go
update syscolumns set colstat = 0 --turn off bit 1 which indicates identity column
where id = object_id('table_name') and name = 'column_name'
go
exec sp_configure 'allow update', 0
go
reconfigure with override
go
***********************
Next, you can set the relationships so they'll update the foreign key references. Or else you need to turn off relationship enforcement. This SO link shows how:
How can foreign key constraints be temporarily disabled using T-SQL?
Now, you can do your updates. I wrote a short script to write all my update SQL based on the same column name (in my case, I needed to increase the CaseID by 1,000,000:
select
'update ['+c.table_name+'] SET ['+Column_Name+']=['+Column_Name+']+1000000'
from Information_Schema.Columns as c
JOIN Information_Schema.Tables as t ON t.table_Name=c.table_name and t.Table_Schema=c.table_schema and t.table_type='BASE TABLE'
where Column_Name like 'CaseID' order by Ordinal_position
Lastly, re-enable referential integrity and then re-enable the Identity column on the primary key.
Note: I see some folks on these questions ask WHY. In my case, I have to merge data from a second production instance into a master DB so I can shut down the second instance. I just need all the PK/FKs of operations data to not collide. Meta-data FKs are identical.
Here's my tables:
CREATE TABLE IF NOT EXISTS message_threads (
thread_id integer primary key autoincrement NOT NULL,
user_id integer NOT NULL,
last_checked timestamp NOT NULL DEFAULT '0',
last_updated timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP
)
CREATE TABLE IF NOT EXISTS messages (
message_id integer primary key autoincrement NOT NULL,
thread_id integer NOT NULL,message_type integer NOT NULL DEFAULT '0',
message_content varchar(500) NOT NULL,
message_date timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
sent integer NOT NULL DEFAULT '0'
);
Here's the error I'm getting:
Could not prepare statement (1 no such column: m.message_date)
Here's the query that I'm using (This query works in MySQL, as I tested it in PHPMyAdmin with a dummy table)
SELECT * FROM messages m, message_threads t
WHERE m.thread_id = t.thread_id
ORDER BY t.last_updated, t.thread_id, m.message_date;
I'm using WebSQL (which I think is SQLite)
FULL WebSQL CODE
$rootScope.database = openDatabase('application.db', '1.0', 'Application database', 1024 * 1024);
$rootScope.database.transaction(function(tx) {
tx.executeSql("CREATE TABLE IF NOT EXISTS message_threads (thread_id integer primary key autoincrement NOT NULL, user_id integer NOT NULL, last_checked timestamp NOT NULL DEFAULT '0', last_updated timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP);");
tx.executeSql("CREATE TABLE IF NOT EXISTS messages (message_id integer primary key autoincrement NOT NULL,thread_id integer NOT NULL,message_type integer NOT NULL DEFAULT '0',message_content varchar(500) NOT NULL, message_date timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, sent integer NOT NULL DEFAULT '0');");
});
// Empty messages/threads for testing purposes
$rootScope.database.transaction(function(tx) {
tx.executeSql("DELETE FROM messages;");
tx.executeSql("DELETE FROM message_threads;");
});
$rootScope.database.transaction(function(tx) {
tx.executeSql("INSERT INTO message_threads (user_id) VALUES (?);", [0]);
tx.executeSql("INSERT INTO messages (thread_id, message_content, sent) VALUES (?, ?, ?);", [1, "How are you doing?", 1]);
tx.executeSql("INSERT INTO messages (thread_id, message_content) VALUES (?, ?);", [1, "Good you?"]);
});
$rootScope.database.transaction(function(tx) {
tx.executeSql("SELECT * FROM messages m, message_threads t WHERE m.thread_id = t.thread_id ORDER BY t.last_updated, t.thread_id, m.message_date", [], function(tx, rs) {
console.log(JSON.stringify(rs));
}, function(tx, err) {
alert("Error: " + err.message);
});
});
I should add that the query works fine using DBBrowser for SQLite.
Chances are that your database has an older version of the table without the column.
CREATE TABLE IF NOT EXISTS only creates a new table with the given specification if a table by the same name does not exist. It does nothing to make sure the columns are there.
To fix it, either remove your database file, or use DROP TABLE to get rid of your old tables before recreating them.
I have created a fresh new sqlite database and tested both of your create queries using the plain command line sqlite.exe version 3.8.0.2 on windows 7. There were no errors.
Then I have used SQLiteStudio Version 3.0.6 and entered some dummy data and executed your select query. Again no issues.
The tools that I have used can only deal with sqlite. Therefore, it seems to me that there are some configuration issues with your tools.
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 Vélez 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.