检查列是否已存在，如果不存在，则返回sqlite中的Alter Table

I want to alter a table of sqlite in my app.

我想在我的应用程序中更改sqlite表。

now , i want to check that if that column already exists in my table or not ?

现在，我想检查一下，如果该列已经存在于我的表中？

hence if not exist i want to add that column with alter table syntex.

因此，如果不存在，我想用alter table syntex添加该列。

currently i am using .

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);
    }
}

2 个解决方案

#1

Use following function for checking if column exists. Not checked practically so you may have to check syntax. Concept is like if you are able to create prepared statement than column exists otherwise not.

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，否则不存在。

-(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:

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
}

#2

PRAGMA table_info(table-name);

PRAGMA table_info（table-name）;

This Pragma is used to get list of columns in your table.

此Pragma用于获取表中的列列表。

For more details, visit here

有关详细信息，请访问此处

- (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;
}

#1