Reputation: 25086

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?

Upvotes: 1129

Answers (30)

NoComprende

Reputation: 751

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;

}

Upvotes: 0

Gratzy

Reputation: 2908

This may be new to SQLiteConnection but there is a much easier way to do this now.

        string appFolder = FileSystem.Current.AppDataDirectory;
        string fileName = Path.Combine(appFolder, "mydb.db");

        using (SQLiteConnection con = new SQLiteConnection(fileName))
        {
            if (con.GetTableInfo("tablename").Count() == 0) 
            {
                con.CreateTable<myObjectName>();
            }
        }

This seems to work great and within the SQLiteObject vs sql commands.

Upvotes: 0

Mark

Reputation: 21

As noted you can find if a table exists using the following query

SELECT name FROM sqlite_master WHERE type='table' AND name='{table_name}';

However, this query will search the schema main.sqlite_master only

If you have one or more attached databases using

ATTACH DATABASE AS schema-name

Then tables will not be found in the attached schema

To know if a table exists in schemas other than 'main' you need to iterate through all schema eg schema-name.sqlite_master.

To solve this I see 2 options

Remember the attached databases schema names and iterate over those
Find all the attached databases using sqlite native functionality and iterate over this list

The 2nd option can be done by using the following

select * from pragma_database_list

This returns the order, schema-name and DATABASE and you can then iterate over all {schema-name}.sqlite_master and find if a table exists and in what schema (multiples could exist) ref: https://www.sqlite.org/dbpage.html#using_sqlite_dbpage_on_attach_ed_databases is the only reference. I can find to this and therefore cannot see if this is a maintained part of sqlite's functionality

Upvotes: 2

Brian Olson

Reputation: 1

Look into the "try - throw - catch" construct in C++. Most other programming languages have a similar construct for handling errors.

Upvotes: -3

Abednego Nasila

Reputation: 165

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

Upvotes: 3

Luis Tejeda

Reputation: 1

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; }

}

Upvotes: 0

Mohamed Reda

Reputation: 1617

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()

Upvotes: 0

StickySli

Reputation: 101

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.

Upvotes: 1

Anton Gogolev

Reputation: 115859

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;

Upvotes: 51

yuviscor

Reputation: 29

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.

Upvotes: 0

sn0wbl1nd

Reputation: 46

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.

Upvotes: 2

Shivam Pokhriyal

Reputation: 1104

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;
}

Upvotes: 0

Stephen Quan

Reputation: 26189

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;
}

Upvotes: 228

PoorLuzer

Reputation: 25086

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)

Upvotes: 1240

Douglas Goodall

Reputation: 121

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

Upvotes: 7

Matthew Joughin

Reputation: 121

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);
}

Upvotes: 3

AnKr

Reputation: 453

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'

Upvotes: 6

Diego Vélez

Reputation: 655

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

Upvotes: 41

Piotr Rodak

Reputation: 1941

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

Upvotes: 1

Zappescu

Reputation: 1439

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);
        });
    });
}

Upvotes: 0

Rakesh Chaudhari

Reputation: 3510

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.

Upvotes: 38

asmad

Reputation: 387

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.

Upvotes: 7

Grz

Reputation: 39

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).

Upvotes: 3

pacheco

Reputation: 139

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"

Upvotes: 13

user655489

Reputation: 1326

If you're using fmdb, I think you can just import FMDatabaseAdditions and use the bool function:

[yourfmdbDatabase tableExists:tableName].

Upvotes: 24

Franz Fahrenkrog Petermann

Reputation: 159

Use

SELECT 1 FROM table LIMIT 1;

to prevent all records from being read.

Upvotes: 3

Scott Deerwester

Reputation: 3977

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';

Upvotes: 11

Brice M. Dempsey

Reputation: 2161

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

Upvotes: 39

arthur johnston

Reputation: 6862

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

Upvotes: 671

DroidGrailer

Reputation: 99

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;
    }
}

Upvotes: 9

How do I check in SQLite whether a table exists?

Answers (30)

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