如何在SQLITE中删除或添加列?

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

我根据Sqlite推荐的方法写了一个Java实现:

private void dropColumn(SQLiteDatabase db,
        ConnectionSource connectionSource,
        String createTableCmd,
        String tableName,
        String[] colsToRemove) throws java.sql.SQLException {

    List<String> updatedTableColumns = getTableColumns(tableName);
    // Remove the columns we don't want anymore from the table's list of columns
    updatedTableColumns.removeAll(Arrays.asList(colsToRemove));

    String columnsSeperated = TextUtils.join(",", updatedTableColumns);

    db.execSQL("ALTER TABLE " + tableName + " RENAME TO " + tableName + "_old;");

    // Creating the table on its new format (no redundant columns)
    db.execSQL(createTableCmd);

    // Populating the table with the data
    db.execSQL("INSERT INTO " + tableName + "(" + columnsSeperated + ") SELECT "
            + columnsSeperated + " FROM " + tableName + "_old;");
    db.execSQL("DROP TABLE " + tableName + "_old;");
}

为了获得表的列，我使用了“PRAGMA table_info”:

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

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

    return columns;
}

实际上我在我的博客上写过，你可以在那里看到更多的解释:

http://udinic.wordpress.com/2012/05/09/sqlite-drop-column-support/

2012-05-14 10:12:32

其他回答

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

正如您在图中看到的，只支持ADD COLUMN。不过，有一个(有点沉重的)变通方法:http://www.sqlite.org/faq.html#q11

2011-12-09 07:07:58

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。

2018-02-05 11:15:28

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 
);

2015-09-17 08:57:54

在SQLite 3中不能删除特定的列。参见FAQ。

2012-09-26 07:12:27