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
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
SQLite 3.35.0引入了对ALTER TABLE DROP COLUMN的支持。
ALTER TABLE DROP COLUMN语法用于从表中删除现有列。DROP COLUMN命令从表中删除指定的列,并重写整个表以清除与该列相关的数据。DROP COLUMN命令仅在列未被模式的任何其他部分引用、不是PRIMARY KEY且没有UNIQUE约束时才有效。
下面的语法是有效的:
ALTER TABLE <TABLENAME> DROP COLUMN <COLUMNNAME>;
ALTER TABLE <TABLENAME> DROP <COLUMNNAME>;
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();
}
}
我的解,只需要调用这个方法。
public static void dropColumn(SQLiteDatabase db, String tableName, String[] columnsToRemove) throws java.sql.SQLException {
List<String> updatedTableColumns = getTableColumns(db, tableName);
updatedTableColumns.removeAll(Arrays.asList(columnsToRemove));
String columnsSeperated = TextUtils.join(",", updatedTableColumns);
db.execSQL("ALTER TABLE " + tableName + " RENAME TO " + tableName + "_old;");
db.execSQL("CREATE TABLE " + tableName + " (" + columnsSeperated + ");");
db.execSQL("INSERT INTO " + tableName + "(" + columnsSeperated + ") SELECT "
+ columnsSeperated + " FROM " + tableName + "_old;");
db.execSQL("DROP TABLE " + tableName + "_old;");
}
辅助方法获取列:
public static 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;
}
至少在3.37.0版本,sqlite3支持DROP COLUMN
修改表SQLite
SQLite支持ALTER TABLE的一个有限子集。SQLite中的ALTER TABLE命令允许用户重命名表或向现有表添加新列。不能重命名列、删除列或从表中添加或删除约束。
您可以:
创建新表作为您要更改的表, 复制所有数据, 丢掉旧桌子, 重新命名新文件。
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。