我正在尝试检查表中的记录是否已存在.
我怎么能这样做？
我已经写了以下代码：
@H_403_5@string dbName = "Data Source=searchindex.db"; sqliteConnection con = new sqliteConnection(dbName); con.Open(); sqliteCommand cmd = new sqliteCommand(con); // If this sql request return false cmd.CommandText = "SELECT rowid FROM wordlist WHERE word='word'"; cmd.ExecuteNonQuery(); // then add record in table cmd.CommandText = "INSERT INTO wordlist(word) VALUES ('word')";
要检查该记录是否存在,您可以简化代码
@H_403_5@cmd.CommandText = "SELECT count(*) FROM wordlist WHERE word='word'";
int count = Convert.ToInt32(cmd.ExecuteScalar());
if(count == 0)
{
cmd.CommandText = "INSERT INTO wordlist(word) VALUES ('word')";
cmd.ExecuteNonQuery();
}
ExecuteScalar将返回查询返回的第一行的第一列.
(该链接适用于sqlServer,但它与sqlite完全相同,因为sqliteCommand应该实现IDbCommand接口)
另一种使用方法如下
@H_403_5@cmd.CommandText = "INSERT INTO wordlist (word) SELECT ('word') WHERE NOT EXISTS (SELECT 1 FROM wordlist WHERE word = 'word');"; cmd.ExecuteNonQuery();