我想在我的应用程序中更改sqlite表。
现在,我想检查一下我的表中是否已存在该列?
因此如果不存在,我想用alter table syntex添加该列。
目前我正在使用。
-(void) alterDB{
sqlite3_stmt *statement;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *databasePath = [documentsDirectory stringByAppendingPathComponent:DATABASE_NAME];
if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK)
{
NSString *updateSQL = [NSString stringWithFormat: @"ALTER TABLE diagramInfo ADD COLUMN testColumn VARCHAR"];
const char *update_stmt = [updateSQL UTF8String];
sqlite3_prepare_v2(database, update_stmt, -1, &statement, NULL);
if(sqlite3_step(statement)==SQLITE_DONE)
{
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"DB altered" message:@"Success" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
[alert release];
alert=nil;
}
else
{
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"DB Updation" message:@"DB not Altered" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
[alert release];
alert=nil;
}
// Release the compiled statement from memory
sqlite3_finalize(statement);
sqlite3_close(database);
}
}
答案 0 :(得分:32)
使用以下函数检查列是否存在。实际上没有检查,所以你可能需要检查语法。概念就像你能够创建预备语句而不是列存在,否则不是。
-(BOOL)checkColumnExists
{
BOOL columnExists = NO;
sqlite3_stmt *selectStmt;
const char *sqlStatement = "select yourcolumnname from yourtable";
if(sqlite3_prepare_v2(yourDbHandle, sqlStatement, -1, &selectStmt, NULL) == SQLITE_OK)
columnExists = YES;
return columnExists;
}
Swift 3.2:
private func tableHasColumn(db: OpaquePointer, tableName: String, columnName: String) -> Bool {
var retVal = false
var tableColumnsQueryStatement: OpaquePointer? = nil
if sqlite3_prepare_v2(db, "PRAGMA table_info(\(tableName));",
-1,
&tableColumnsQueryStatement,
nil) == SQLITE_OK {
while (sqlite3_step(tableColumnsQueryStatement) == SQLITE_ROW) {
let queryResultCol1 = sqlite3_column_text(tableColumnsQueryStatement, 1)
let currentColumnName = String(cString: queryResultCol1!)
if currentColumnName == columnName {
retVal = true
break
}
}
}
return retVal
}
答案 1 :(得分:9)
PRAGMA table_info(table-name);
此Pragma用于获取表格中的列列表。
- (BOOL)checkForField
{
NSString *desiredColumn = @"tblName";
const char *sql = "PRAGMA table_info(tblTest)";
sqlite3_stmt *stmt;
if (sqlite3_prepare_v2(db, sql, -1, &stmt, NULL) != SQLITE_OK)
{
return NO;
}
while(sqlite3_step(stmt) == SQLITE_ROW)
{
NSString *fieldName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(stmt, 1)];
if([desiredColumn isEqualToString:fieldName])
return YES;
}
return NO;
}