I am trying to copy all data from sqlite table to another one (reason being changing primary key and recommended way is to create new table, copy data, rename, etc).
Something along:
insert into new_table select * from old_table;
drop old_table;
alter table new_table rename to old_table;
Now problem is, that sometimes when I create new table, it's order of columns is not the same and data is completely messed up. Not sure why, probably cause some people have brand new table and some have old table which lived trough lot of upgrade scripts. Anyway my point is, I need to make sure every column is inserted into correct column. I can for sure just name all the columns manually, but I'd like this to work even if I add some columns in future and also for other tables. I can probably somehow query name of columns and then construct query in language that I am using above (kotlin), but I'd like to do this on db level if possible.
It's on android, but not very relevant to the question :)
Thanks!
Sadly I had add 1 extra query to get columns.
Other queries had all columns specifically mentioned instead of using star to ensure correct order. My kotlin way:
fun columns(db: SQLiteDatabase, tableName: String): List<String> {
val sql = "pragma table_info($tableName)"
return db.rawQuery(sql, arrayOf()).use { cursor ->
(1..cursor.count).map {
cursor.moveToNext()
cursor.getString(cursor.getColumnIndexOrThrow("name"))
}
}
}
fun copyFromTableToTable(db: SQLiteDatabase, originalTableName: String, backupTableName: String) {
val columns = columns(db, backupTableName).joinToString(separator = ",")
db.execSQL("""INSERT INTO $backupTableName
($columns)
SELECT $columns FROM $originalTableName
""".trimMargin())
//db.execSQL("DROP TABLE $originalTableName;")
//db.execSQL("ALTER TABLE $backupTableName RENAME TO $originalTableName;")
}
I have a collection in DocumentDB with objects that look like this:
{
"id":"1de03a93-729d-43da-985a-12584079b4f8",
"Components":[
{
"Name":"MyComponentName1",
"Value": 12345
},
{
"Name":"MyComponentName2",
"Value": 34567
},
{
"Name":"MyComponentName3",
"Value": 56789
}
]
...other properties irrelevant to question...
}
When querying CosmosDB, I have the following query:
SELECT VALUE d FROM c
JOIN d IN c.Components
WHERE d.Name="MyComponentName1"
which correctly returns:
{
"Name":"MyComponentName1",
"Value":12345
}
However, when I attempt to query based on a String operator:
SELECT VALUE d FROM c
JOIN d IN c.Components
WHERE CONTAINS(d.Name,'MyComponent') --OR STARTSWITH OR ENDSWITH
I get no results.
If I take the same query as above but I add an id restriction to the where clause:
SELECT VALUE d FROM c
JOIN d IN c.Components
WHERE CONTAINS(d.Name,'MyComponent')
AND c.id = "1de03a93-729d-43da-985a-12584079b4f8"
I get back the results I expect, but obviously only for that id. I need all of the documents that match the String operator.
Is this a bug with CosmosDB, or am I doing something wrong?
Nick,
Make sure that you're following all the continuations when you execute this query. Please keep in mind that the query w/ Contains will result in a full scan and hence it might not finish in a single continuation. This is the same case w/ EndsWith. For StartsWith, however, it should utilize the index, but only if the collection index policy define range index on strings; otherwise, it will still be a scan.
I'm using the latest ArangoDB 3.1 on Windows 10.
Here I want to remove the collection document and edge document using the for loop. But I'm getting an error like document not found (vName).
vName contains the many collection names. But I dunno how to use it in for loop.
This is the AQL I am using to remove the documents from the graph:
LET op = (FOR v, e IN 1..1 ANY 'User/588751454' GRAPH 'my_graph'
COLLECT vid = v._id, eid = e._id
RETURN { vid, eid }
)
FOR doc IN op
COLLECT vName = SPLIT(doc.vid,'/')[0],
vid = SPLIT(doc.vid,'/')[1],
eName = SPLIT(doc.eid,'/')[0],
eid = SPLIT(doc.eid,'/')[1]
REMOVE { _key: vid } in vName
Return output im getting from the AQL (Web UI screenshot)
vName is a variable introduced by COLLECT. It is a string with the collection name of a vertex (extracted from vid / v._id). You then try to use it in the removal operation REMOVE { ... } IN vName.
AQL does not support dynamic collection names however, collection names must be known at query compile time:
Each REMOVE operation is restricted to a single collection, and the collection name must not be dynamic.
Source: https://docs.arangodb.com/3.2/AQL/Operations/Remove.html
So, you either have to hardcode the collection into the query, e.g. REMOVE { ... } IN User, or use the special bind parameter syntax for collections, e.g. REMOVE { ... } IN ##coll and bind parameters: {"#coll": "User", ...}.
This also means that REMOVE can only delete documents in a single collection.
It's possible to workaround the limitation somewhat by using subqueries like this:
LET x1 = (FOR doc IN User REMOVE aa IN User)
LET x2 = (FOR doc IN relations REMOVE bb IN relations)
RETURN 1
The variables x1 and x2 are syntactically required and receive an empty array as subquery result. The query also requires a RETURN statement, even if we don't expect any result.
Do not attempt to remove from the same collection twice in the same query though, as it would raise a access after data-modification error.
"IN" query is not working. Please guide me if i am wrong.
KaizenResultsInformationTable is MasterTable having field "recordinfo", this field contains Child table Ids as string.
kaizenResultsRecordInformationTable is Childtable having field "recordId".
I have to match records of child.
Query:
select recordinfo from KaizenResultsInformationTable
Output: ;0;1;2;3;4;5;6;7;8;9;10
Query:
select substr(replace(recordinfo,';','","'),3,length(recordinfo))
from KaizenResultsInformationTable`
Output: "0","1","2","3","4","5"
This query is not working:
select * from kaizenResultsRecordInformationTable
where substr(recordid,0,2) in (
select substr(replace(recordinfo,';','","'),3,length(recordinfo))
from KaizenResultsInformationTable
)
This query is working:
select * from kaizenResultsRecordInformationTable
where substr(recordid,0,2) in ("0","1","2","3","4","5")
You can't use in like that. In your second query, you are passing in a single string containing a comma-separated list of values.
It is better to represent a list of IDs as one record for each value.
Also, I'm not sure why you are taking a substring of your recordid. You should usually be storing one value per column.
However, if you can't change the schema, you can use string matching with 'like' instead of 'in'. Something like this should work:
select a.* from kaizenResultsRecordInformationTable a
join KaizenResultsInformationTable b
on (';'+b.recordinfo+';') LIKE ('%;'+trim(substr(recordid,0,2))+';%')
So if your recordinfo looks like 1;2;3;4;5;6, and your substr(recordid,0,2) looks like 1, this will include that row if ";1;2;3;4;5;6;" LIKE "%;1;%", which is true.
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.