我想在sqlite数据库中删除或添加列

我正在使用以下查询删除列。

ALTER TABLE TABLENAME DROP COLUMN COLUMNNAME

但它会产生错误

System.Data.SQLite.SQLiteException: SQLite error
near "DROP": syntax error

当前回答

我猜您想做的是数据库迁移。在SQLite中不存在“删除”列。但是,您可以使用ALTER表查询添加一个额外的列。

其他回答

我重写了@Udinic答案,以便代码自动生成表创建查询。它也不需要ConnectionSource。它还必须在事务中完成此操作。

public static String getOneTableDbSchema(SQLiteDatabase db, String tableName) {
    Cursor c = db.rawQuery(
            "SELECT * FROM `sqlite_master` WHERE `type` = 'table' AND `name` = '" + tableName + "'", null);
    String result = null;
    if (c.moveToFirst()) {
        result = c.getString(c.getColumnIndex("sql"));
    }
    c.close();
    return result;
}

public List<String> getTableColumns(SQLiteDatabase db, String tableName) {
    ArrayList<String> columns = new ArrayList<>();
    String cmd = "pragma table_info(" + tableName + ");";
    Cursor cur = db.rawQuery(cmd, null);

    while (cur.moveToNext()) {
        columns.add(cur.getString(cur.getColumnIndex("name")));
    }
    cur.close();

    return columns;
}

private void dropColumn(SQLiteDatabase db, String tableName, String[] columnsToRemove) {
    db.beginTransaction();
    try {
        List<String> columnNamesWithoutRemovedOnes = getTableColumns(db, tableName);
        // Remove the columns we don't want anymore from the table's list of columns
        columnNamesWithoutRemovedOnes.removeAll(Arrays.asList(columnsToRemove));

        String newColumnNamesSeparated = TextUtils.join(" , ", columnNamesWithoutRemovedOnes);
        String sql = getOneTableDbSchema(db, tableName);
        // Extract the SQL query that contains only columns
        String oldColumnsSql = sql.substring(sql.indexOf("(")+1, sql.lastIndexOf(")"));

        db.execSQL("ALTER TABLE " + tableName + " RENAME TO " + tableName + "_old;");
        db.execSQL("CREATE TABLE `" + tableName + "` (" + getSqlWithoutRemovedColumns(oldColumnsSql, columnsToRemove)+ ");");
        db.execSQL("INSERT INTO " + tableName + "(" + newColumnNamesSeparated + ") SELECT " + newColumnNamesSeparated + " FROM " + tableName + "_old;");
        db.execSQL("DROP TABLE " + tableName + "_old;");
        db.setTransactionSuccessful();
    } catch {
        //Error in between database transaction 
    } finally {
        db.endTransaction();
    }


}

正如其他人指出的那样

不能重命名列、删除列或添加或 从表中删除约束。

来源:http://www.sqlite.org/lang_altertable.html

而您总是可以创建一个新表,然后删除旧表。 我将尝试用一个例子来解释这种解决方法。

sqlite> .schema
CREATE TABLE person(
 id INTEGER PRIMARY KEY, 
 first_name TEXT,
 last_name TEXT, 
 age INTEGER, 
 height INTEGER
);
sqlite> select * from person ; 
id          first_name  last_name   age         height    
----------  ----------  ----------  ----------  ----------
0           john        doe         20          170       
1           foo         bar         25          171       

现在要从该表中删除列的高度。

创建另一个名为new_person的表

sqlite> CREATE TABLE new_person(
   ...>  id INTEGER PRIMARY KEY, 
   ...>  first_name TEXT, 
   ...>  last_name TEXT, 
   ...>  age INTEGER 
   ...> ) ; 
sqlite> 

现在从旧表复制数据

sqlite> INSERT INTO new_person
   ...> SELECT id, first_name, last_name, age FROM person ;
sqlite> select * from new_person ;
id          first_name  last_name   age       
----------  ----------  ----------  ----------
0           john        doe         20        
1           foo         bar         25        
sqlite>

现在删除person表并将new_person重命名为person

sqlite> DROP TABLE IF EXISTS person ; 
sqlite> ALTER TABLE new_person RENAME TO person ;
sqlite>

如果你使用。schema,你会看到

sqlite>.schema
CREATE TABLE "person"(
 id INTEGER PRIMARY KEY, 
 first_name TEXT, 
 last_name TEXT, 
 age INTEGER 
);

您现在还可以使用DB浏览器为SQLite操作列

public void DeleteColFromTable(String DbName, String TableName, String ColName){
    SQLiteDatabase db = openOrCreateDatabase(""+DbName+"", Context.MODE_PRIVATE, null);
    db.execSQL("CREATE TABLE IF NOT EXISTS "+TableName+"(1x00dff);");
    Cursor c = db.rawQuery("PRAGMA table_info("+TableName+")", null);
    if (c.getCount() == 0) {

    } else {
        String columns1 = "";
        String columns2 = "";
        while (c.moveToNext()) {
            if (c.getString(1).equals(ColName)) {
            } else {
                columns1 = columns1 + ", " + c.getString(1) + " " + c.getString(2);
                columns2 = columns2 + ", " + c.getString(1);
            }
            if (c.isLast()) {
                db.execSQL("CREATE TABLE IF NOT EXISTS DataBackup (" + columns1 + ");");
                db.execSQL("INSERT INTO DataBackup SELECT " + columns2 + " FROM "+TableName+";");
                db.execSQL("DROP TABLE "+TableName+"");
                db.execSQL("ALTER TABLE DataBackup RENAME TO "+TableName+";");
            }
        }
    }
}

只需要调用一个方法

DeleteColFromTable("Database name","Table name","Col name which want to delete");

基于http://www.sqlite.org/faq.html#q11上的信息在Python中实现。

import sqlite3 as db
import random
import string

QUERY_TEMPLATE_GET_COLUMNS = "PRAGMA table_info(@table_name)"
QUERY_TEMPLATE_DROP_COLUMN = """
  BEGIN TRANSACTION;
  CREATE TEMPORARY TABLE @tmp_table(@columns_to_keep);
  INSERT INTO @tmp_table SELECT @columns_to_keep FROM @table_name;
  DROP TABLE @table_name;
  CREATE TABLE @table_name(@columns_to_keep);
  INSERT INTO @table_name SELECT @columns_to_keep FROM @tmp_table;
  DROP TABLE @tmp_table;
  COMMIT;
"""

def drop_column(db_file, table_name, column_name):
    con = db.connect(db_file)
    QUERY_GET_COLUMNS = QUERY_TEMPLATE_GET_COLUMNS.replace("@table_name", table_name)
    query_res = con.execute(QUERY_GET_COLUMNS).fetchall()
    columns_list_to_keep = [i[1] for i in query_res if i[1] != column_name]
    columns_to_keep = ",".join(columns_list_to_keep)
    tmp_table = "tmp_%s" % "".join(random.sample(string.ascii_lowercase, 10))
    QUERY_DROP_COLUMN = QUERY_TEMPLATE_DROP_COLUMN.replace("@table_name", table_name)\
        .replace("@tmp_table", tmp_table).replace("@columns_to_keep", columns_to_keep)
    con.executescript(QUERY_DROP_COLUMN)
    con.close()

drop_column(DB_FILE, TABLE_NAME, COLUMN_NAME)

这个脚本首先创建随机的临时表,并只插入必要列的数据,除了将要删除的列。然后根据临时表恢复原表,删除临时表。