[yunqa.de] Re: TDISQLite3UniDirQuery record count [this does work]
- From: Todd Cary <todd@xxxxxxxxxxxxxxxxxx>
- To: yunqa@xxxxxxxxxxxxx
- Date: Fri, 19 Mar 2010 16:21:18 -0700
Ralf -
On the following line, I get the error SQLite Error 21 - library routine
called out of sequence.
sqlite3_check(
sqlite3_prepare_v2(DB, Pointer(SQL), Length(SQL), @Stmt, nil), DB);
function sqlite3_exists_table_column() works great! Thanks!
Todd
On 3/19/2010 3:17 AM, Delphi Inspiration wrote:
At 23:06 18.03.2010, Todd Cary wrote:
I want to determine if a table exists, so I have this code:
...
sCmd := 'SELECT name FROM sqlite_master ' +
'WHERE type=''table'' AND name = ''' + sTableName + '''';
SQLGenQry.SelectSQL := sCmd;
SQLGenQry.Open;
Result := (SQLGenQry.RecordCount = 1);
...
SQLGenQry is a TDISQLite3UniDirQuery and the RecordCount is always -1. Am I
making an error?
TDISQLite3UniDirQuery is a uni-directional TDataSet. It does not buffer
multiple records in memory. Hence the RecordCount property is not available --
it always returns -1.
The following function implements a more efficient way to test if a table
exists. It has virtually no overhead and uses the DISQLite3Api unit only:
function sqlite3_exists_table(
const DB: sqlite3_ptr;
const TableName: Utf8String;
const DatabaseName: Utf8String = ''): Boolean;
var
SQL: Utf8String;
Stmt: sqlite3_stmt_ptr;
begin
SQL := 'SELECT 1 FROM ' + sqlite3_database_master(DatabaseName) +
' WHERE type=''table'' AND name=' + DISQLite3Api.QuotedStr(TableName);
sqlite3_check(
sqlite3_prepare_v2(DB, Pointer(SQL), Length(SQL), @Stmt, nil), DB);
Result := sqlite3_check(
sqlite3_step(Stmt), DB) = SQLITE_ROW;
sqlite3_check(
sqlite3_finalize(Stmt), DB);
end;
Applications pass the database handle and the table name. The name of the
(attached) database is optional and defaults to the main database.
sqlite3_exists_table() returns True if the table exists in the database and
False if it does not exist.
Ralf
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