I would like to create an unique constraint on a TEXT column that will only affect the non-empty cells. (Each cell must be unique if and only if it contains some characters).
I tried this, but it raised an exception :
db.execSQL("CREATE TABLE tables (" +
"table_id INTEGER PRIMARY KEY, " +
"table_name TEXT, " +
"table_number INTEGER, " +
"table_alias TEXT, " +
"UNIQUE(table_alias) WHERE table_alias != '' ON CONFLICT IGNORE);"
Any idea how can I achieve this?
In a UNIQUE column, NULL values are considered distinct. (Don't ask why, this is just how SQL works.)
So replace the emtry strings with NULLs.
My code follows:
SELECT COUNT(_id) AS count FROM general WHERE _id = 1 CASE WHEN count > 0 THEN UPDATE general SET userGivenId = 'xxx' WHERE _id = 1 ELSE INSERT INTO general (userGivenId) VALUES ('xxx' ) END
With the error:
android.database.sqlite.SQLiteException: near "CASE": syntax error: , while compiling: SELECT COUNT(_id) AS count FROM general WHERE _id = 1 CASE WHEN count > 0 THEN UPDATE general SET userGivenId = 'xxx' WHERE _id = 1 ELSE INSERT INTO general (userGivenId) VALUES ('xxx' ) END
This is the shortest query I will use. Why I do this is because my other queries will have rows that needs to be updated but some may not be touched. Using replace will replace all the data (at least that is how it works for me on my Android phone). For instance my File class will have a filePath, but sometimes the response from the server will return null and I am only to update the File IF the server returns a new File.
Did I forget to write anything?
SQLite does not have any control logic because this would not make sense in an embedded database (there is no separate server machine/process whose asynchronous execution could improve performance).
CASE can be used only for expressions, not for entire commands.
Handle the control logic in your app:
Cursor c = db.rawQuery("SELECT 1 FROM general WHERE _id = 1", null);
if (c.moveToFirst())
db.execSQL("UPDATE general SET userGivenId = 'xxx' WHERE _id = 1");
else
db.execSQL("INSERT INTO general (userGivenId) VALUES ('xxx')");
For these particular commands, if you have a unique constraint on the _id column (and a primary key is constrained to be unique), you can use the INSERT OR REPLACE command:
INSERT OR REPLACE INTO general(_id, userGivenId) VALUES(1, 'xxx')
I am trying to insert a string which contains '%' using QsqlQuery but I am always getting an error of type QSqlError::TransactionError with the message
"near "%": syntax error Unable to execute statement"
I have tried several ways to escape the "%" but I am still getting that error message. Please see the code snippet below.
query.exec(QString("INSERT INTO my_table (name, address) VALUES (\"%1\", \"%2\")")
.arg("Harry", "#302%%1,..."));
In place of "%%", I have tried "\%", "\%", but still it didn't work and I am having the same error message.
In SQL, strings are delimited with ', not ".
Anyway, you should use parameters:
query.prepare("INSERT INTO my_table (name, address) VALUES (?, ?)");
query.addBindValue("Harry");
query.addBindValue("#302%%1,...");
query.exec();
Ok, so I have a basic table called "ledger", it contains fields of various types, integers, varchar, etc.
In my program, I used to use a query with no "from" predicate to collect all of the rows, which of course works fine. But... I changed my code to allow selecting one row at a time using "where acctno = x" (where X is the account number I want to select at the time).
I thought this must be a bug in the client library for my programming language, so I tested it in the SQLite command-line client - and it still doesn't work!
I am relatively new to SQLite, but I have been using Oracle, MS SQL Server, etc. for years and never seen this type of issue before.
Other things I can tell you:
* Queries using other integer fields also don't work
* Queries on char fields work
* Querying it as a string (with the account number on quotes) still doesn't work. (I thought maybe the numbers were stored as a string inadvertently).
* Accessing rows by rowid works fine - which is why I can edit the database with GUI tools with no noticeable problem.
Examples:
Query with no WHERE (works fine):
1|0|0|JPY|8|Paid-In Capital|C|X|0|X|0|0||||0|0|0|
0|0|0|JPY|11|Root Account|P|X|0|X|0|0|SYSTEM|20121209|150000|0|0|0|
3|0|0|JPY|13|Mitsubishi Bank Futsuu|A|X|0|X|0|0|SYSTEM|20121209|150000|0|0|0|
4|0|0|JPY|14|Japan Post Bank|A|X|0|X|0|0|SYSTEM|20121209|150000|0|0|0|
...
Query with WHERE clause: (no results)
sqlite> select * from ledger where acctno=1;
sqlite>
putting quotes around the 1 above changes nothing.
Interestingly enough, "select * from ledger where acctno > 1" returns results! However since it returns ALL results, it's not terrible useful.
I'm sure someone will ask about the table structure, so here goes:
sqlite> .schema ledger
CREATE TABLE "LEDGER" (
"ACCTNO" integer(10,0) NOT NULL,
"drbal" integer(20,0) NOT NULL,
"crbal" integer(20,0) NOT NULL,
"CURRKEY" char(3,0) NOT NULL,
"TEXTKEY" integer(10,0),
"TEXT" VARCHAR(64,0),
"ACCTYPECD" CHAR(1,0) NOT NULL,
"ACCSTCD" CHAR(1,0),
"PACCTNO" number(10,0) NOT NULL,
"CATCD" number(10,0),
"TRANSNO" number(10,0) NOT NULL,
"extrefno" number(10,0),
"UPDATEUSER" VARCHAR(32,0),
"UPDATEDATE" text(8,0),
"UPDATETIME" TEXT(6,0),
"PAYEECD" number(10,0) NOT NULL,
"drbal2" number(10,0) NOT NULL,
"crbal2" number(10,0) NOT NULL,
"delind" boolean,
PRIMARY KEY("ACCTNO"),
CONSTRAINT "fk_curr" FOREIGN KEY ("CURRKEY") REFERENCES "CURRENCY" ("CUR
RKEY") ON DELETE RESTRICT ON UPDATE CASCADE
);
The strangest thing is that I have other similar tables where this works fine!
sqlite> select * from journalhdr where transno=13;
13|Test transaction ATM Withdrawel 20130213|20130223||20130223||
TransNo in that table is also integer (10,0) NOT NULL - this is what makes me thing it is something to do with the values.
Another clue is that the sort order seems to be based on ascii, not numeric:
sqlite> select * from ledger order by acctno;
0|0|0|JPY|11|Root Account|P|X|0|X|0|0|SYSTEM|20121209|150000|0|0|0|
1|0|0|JPY|8|Paid-In Capital|C|X|0|X|0|0||||0|0|0|
10|0|0|USD|20|Sallie Mae|L|X|0|X|0|0|SYSTEM|20121209|153900|0|0|0|
21|0|0|USD|21|Skrill|A|X|0|X|0|0|SYSTEM|20121209|154000|0|0|0|
22|0|0|USD|22|AES|L|X|0|X|0|0|SYSTEM|20121209|154200|0|0|0|
23|0|0|JPY|23|Marui|L|X|0|X|0|0|SYSTEM|20121209|154400|0|0|0|
24|0|0|JPY|24|Amex JP|L|X|0|X|0|0|SYSTEM|20121209|154500|0|0|0|
3|0|0|JPY|13|Mitsubishi Bank Futsuu|A|X|0|X|0|0|SYSTEM|20121209|150000|0|0|0|
Of course the sort order on journalhdr (where the select works properly) is numeric.
Solved! (sort-of)
The data can be fixed like this:
sqlite> update ledger set acctno = 23 where rowid = 13;
sqlite> select * from ledger where acctno = 25;
25|0|0|JPY|0|Test|L|X|0|X|0|0|SYSTEM|20130224|132500|0|0|0|
Still, if it was stored as strings, then that leave a few questions:
1. Why couldn't I select it as a string using the quotes?
2. How did it get stored as a string since it is a valid integer?
3. How would you go about detecting this problem normally besides noticing bizzarre symptoms?
Although the data would normally be entered by my program, some of it was created by hand using Navicat, so I assume the problem must lie there.
You are victim of SQLite dynamic typing.
Even though SQLite defines system of type affinity, which sets some rules on how input strings or numbers will be converted to actual internal values, but it does NOT prevent software that is using prepared statements to explicitly set any type (and data value) for the column (and this can be different per row!).
This can be shown by this simple example:
CREATE TABLE ledger (acctno INTEGER, name VARCHAR(16));
INSERT INTO ledger VALUES(1, 'John'); -- INTEGER '1'
INSERT INTO ledger VALUES(2 || X'00', 'Zack'); -- BLOB '2\0'
I have inserted second row not as INTEGER, but as binary string containing embedded zero byte. This reproduces your issue exactly, see this SQLFiddle, step by step. You can also execute these commands in sqlite3, you will get the same result.
Below is Perl script that also reproduces this issue
This script creates just 2 rows with acctno having values of integer 1 for first, and "2\0" for second row. "2\0" means string consisting of 2 bytes: first is digit 2, and second is 0 (zero) byte.
Of course, it is very difficult to visually tell "2\0" from just "2", but this is what script below demonstrates:
#!/usr/bin/perl -w
use strict;
use warnings;
use DBI qw(:sql_types);
my $dbh = DBI->connect("dbi:SQLite:test.db") or die DBI::errstr();
$dbh->do("DROP TABLE IF EXISTS ledger");
$dbh->do("CREATE TABLE ledger (acctno INTEGER, name VARCHAR(16))");
my $sth = $dbh->prepare(
"INSERT INTO ledger (acctno, name) VALUES (?, ?)");
$sth->bind_param(1, "1", SQL_INTEGER);
$sth->bind_param(2, "John");
$sth->execute();
$sth->bind_param(1, "2\0", SQL_BLOB);
$sth->bind_param(2, "Zack");
$sth->execute();
$sth = $dbh->prepare(
"SELECT count(*) FROM ledger WHERE acctno = ?");
$sth->bind_param(1, "1");
$sth->execute();
my ($num1) = $sth->fetchrow_array();
print "Number of rows matching id '1' is $num1\n";
$sth->bind_param(1, "2");
$sth->execute();
my ($num2) = $sth->fetchrow_array();
print "Number of rows matching id '2' is $num2\n";
$sth->bind_param(1, "2\0", SQL_BLOB);
$sth->execute();
my ($num3) = $sth->fetchrow_array();
print "Number of rows matching id '2<0>' is $num3\n";
Output of this script is:
Number of rows matching id '1' is 1
Number of rows matching id '2' is 0
Number of rows matching id '2<0>' is 1
If you were to look at resultant table using any SQLite tool (including sqlite3), it will print 2 for second row - they all get confused by trailing 0 inside a BLOB when it gets coerced to string or number.
Note that I had to use custom param binding to coerce type to BLOB and permit null bytes stored:
$sth->bind_param(1, "2\0", SQL_BLOB);
Long story short, it is either some of your client programs, or some of client tools like Navicat which screwed it up.
In SQLite I can run the following query to get a list of columns in a table:
PRAGMA table_info(myTable)
This gives me the columns but no information about what the primary keys may be. Additionally, I can run the following two queries for finding indexes and foreign keys:
PRAGMA index_list(myTable)
PRAGMA foreign_key_list(myTable)
But I cannot seem to figure out how to view the primary keys. Does anyone know how I can go about doing this?
Note: I also know that I can do:
select * from sqlite_master where type = 'table' and name ='myTable';
And it will give the the create table statement which shows the primary keys. But I am looking for a way to do this without parsing the create statement.
The table_info DOES give you a column named pk (last one) indicating if it is a primary key (if so the index of it in the key) or not (zero).
To clarify, from the documentation:
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.
Hopefully this helps someone:
After some research and pain the command that worked for me to find the primary key column name was:
SELECT l.name FROM pragma_table_info("Table_Name") as l WHERE l.pk = 1;
For the ones trying to retrieve a pk name in android, and while using the ROOM library.
#Oogway101's answer was throwing an error: "no such column [your_table_name] ... etc.. etc...
my way of query submition was:
String pkSearch = "SELECT l.name FROM pragma_table_info(" + tableName + ") as l WHERE l.pk = 1;";
database.query(new SimpleSQLiteQuery(pkSearch)
I tried using the (") quotations and still error.
String pkSearch = "SELECT l.name FROM pragma_table_info(\"" + tableName + "\") as l WHERE l.pk = 1;";
So my solution was this:
String pragmaInfo = "PRAGMA table_info(" + tableName + ");";
Cursor c = database.query(new SimpleSQLiteQuery(pragmaInfo));
String id = null;
c.moveToFirst();
do {
if (c.getInt(5) == 1) {
id = c.getString(1);
}
} while (c.moveToNext() && id == null);
Log.println(Log.ASSERT, TAG, "AbstractDao: pk is: " + id);
The explanation is that:
A) PRAGMA table_info returns a cursor with various indices, the response is atleast of length 6... didnt check more...
B) index 1 has the column name.
C) index 5 has the "pk" value, either 0 if it is not a primary key, or 1 if its a pk.
You can define more than one pk so this will not bring an accurate result if your table has more than one (IMHO more than one is bad design and balloons the complexity of the database beyond human comprehension).
So how will this fit into the #Dao? (you may ask...)
When making the Dao "abstract" you have access to a default constructor which has the database in it:
from the docummentation:
An abstract #Dao class can optionally have a constructor that takes a Database as its only parameter.
this is the constructor that will grant you access to the query.
There is a catch though...
You may use the Dao during a database creation with the .addCallback() method:
instance = Room.databaseBuilder(context.getApplicationContext(),
AppDatabase2.class, "database")
.addCallback(
//You may use the Daos here.
)
.build();
If you run a query in the constructor of the Dao, the database will enter a feedback loop of infinite instantiation.
This means that the query MUST be used LAZILY (just at the moment the user needs something), and because the value will never change, it can be stored. and never re-queried.