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
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
其他回答
在SQLite 3中不能删除特定的列。参见FAQ。
我已经改进了user2638929回答，现在它可以保留列类型，主键，默认值等。
public static void dropColumns(SQLiteDatabase database, String tableName, Collection<String> columnsToRemove){
List<String> columnNames = new ArrayList<>();
List<String> columnNamesWithType = new ArrayList<>();
List<String> primaryKeys = new ArrayList<>();
String query = "pragma table_info(" + tableName + ");";
Cursor cursor = database.rawQuery(query,null);
while (cursor.moveToNext()){
String columnName = cursor.getString(cursor.getColumnIndex("name"));
if (columnsToRemove.contains(columnName)){
continue;
}
String columnType = cursor.getString(cursor.getColumnIndex("type"));
boolean isNotNull = cursor.getInt(cursor.getColumnIndex("notnull")) == 1;
boolean isPk = cursor.getInt(cursor.getColumnIndex("pk")) == 1;
columnNames.add(columnName);
String tmp = "`" + columnName + "` " + columnType + " ";
if (isNotNull){
tmp += " NOT NULL ";
}
int defaultValueType = cursor.getType(cursor.getColumnIndex("dflt_value"));
if (defaultValueType == Cursor.FIELD_TYPE_STRING){
tmp += " DEFAULT " + "\"" + cursor.getString(cursor.getColumnIndex("dflt_value")) + "\" ";
}else if(defaultValueType == Cursor.FIELD_TYPE_INTEGER){
tmp += " DEFAULT " + cursor.getInt(cursor.getColumnIndex("dflt_value")) + " ";
}else if (defaultValueType == Cursor.FIELD_TYPE_FLOAT){
tmp += " DEFAULT " + cursor.getFloat(cursor.getColumnIndex("dflt_value")) + " ";
}
columnNamesWithType.add(tmp);
if (isPk){
primaryKeys.add("`" + columnName + "`");
}
}
cursor.close();
String columnNamesSeparated = TextUtils.join(", ", columnNames);
if (primaryKeys.size() > 0){
columnNamesWithType.add("PRIMARY KEY("+ TextUtils.join(", ", primaryKeys) +")");
}
String columnNamesWithTypeSeparated = TextUtils.join(", ", columnNamesWithType);
database.beginTransaction();
try {
database.execSQL("ALTER TABLE " + tableName + " RENAME TO " + tableName + "_old;");
database.execSQL("CREATE TABLE " + tableName + " (" + columnNamesWithTypeSeparated + ");");
database.execSQL("INSERT INTO " + tableName + " (" + columnNamesSeparated + ") SELECT "
+ columnNamesSeparated + " FROM " + tableName + "_old;");
database.execSQL("DROP TABLE " + tableName + "_old;");
database.setTransactionSuccessful();
}finally {
database.endTransaction();
}
}
PS:这里我使用的是android.arch.persistence.db。支持sqlitedatabase，但你可以很容易地修改它使用android.database.sqlite.SQLiteDatabase
这个不同问题的答案是针对修改列的，但我相信，如果你有很多列，并且不想在INSERT语句中手动重新输入大部分列，部分答案也可以产生有用的方法:
https://stackoverflow.com/a/10385666
您可以按照上面链接中描述的方法转储数据库，然后从该转储中获取“create table”语句和“insert”模板，然后按照SQLite FAQ条目“如何从SQLite中现有的表中添加或删除列”中的说明进行操作。(常见问题在本页其他地方有链接。)
Kotlin解决方案，基于这里，还要:
确保临时表不存在 修复了检查默认值的类型，因为当它是Integer时返回String类型(此处报告了此问题)。 避免在希望删除的列不存在时执行任何操作。
object DbUtil {
/** https://stackoverflow.com/a/51587449/878126 */
@JvmStatic
fun dropColumns(database: SQLiteDatabase, tableName: String,
columnsToRemove: Collection<String>) {
val columnNames: MutableList<String> = ArrayList()
val columnNamesWithType: MutableList<String> = ArrayList()
val primaryKeys: MutableList<String> = ArrayList()
val query = "pragma table_info($tableName);"
val cursor = database.rawQuery(query, null)
val columnDefaultIndex = cursor.getColumnIndex("dflt_value")
val columnNameIndex = cursor.getColumnIndex("name")
val columnTypeIndex = cursor.getColumnIndex("type")
val columnNotNullIndex = cursor.getColumnIndex("notnull")
val columnPrimaryKeyIndex = cursor.getColumnIndex("pk")
val sb = StringBuilder()
var foundColumnsToRemove = false
while (cursor.moveToNext()) {
val columnName = cursor.getString(columnNameIndex)
if (columnsToRemove.contains(columnName)) {
foundColumnsToRemove = true
continue
}
val columnType = cursor.getString(columnTypeIndex)
val isNotNull = cursor.getInt(columnNotNullIndex) == 1
val isPrimaryKey = cursor.getInt(columnPrimaryKeyIndex) == 1
columnNames.add(columnName)
sb.clear()
sb.append("`$columnName` $columnType ")
if (isNotNull)
sb.append(" NOT NULL ")
if (cursor.getType(columnDefaultIndex) != Cursor.FIELD_TYPE_NULL) {
//has default value
when (columnType.uppercase()) {
"INTEGER" -> sb.append(" DEFAULT ${cursor.getInt(columnDefaultIndex)} ")
"TEXT" -> sb.append(" DEFAULT \"${cursor.getString(columnDefaultIndex)}\" ")
"REAL" -> sb.append(" DEFAULT ${cursor.getFloat(columnDefaultIndex)} ")
}
}
columnNamesWithType.add(sb.toString())
if (isPrimaryKey)
primaryKeys.add("`$columnName`")
}
cursor.close()
if (!foundColumnsToRemove)
return
val columnNamesSeparated = TextUtils.join(", ", columnNames)
if (primaryKeys.size > 0)
columnNamesWithType.add("PRIMARY KEY(${TextUtils.join(", ", primaryKeys)})")
val columnNamesWithTypeSeparated = TextUtils.join(", ", columnNamesWithType)
database.beginTransaction()
try {
var newTempTableName: String
var counter = 0
while (true) {
newTempTableName = "${tableName}_old_$counter"
if (!isTableExists(database, newTempTableName))
break
++counter
}
database.execSQL("ALTER TABLE $tableName RENAME TO $newTempTableName;")
database.execSQL("CREATE TABLE $tableName ($columnNamesWithTypeSeparated);")
database.execSQL(
"INSERT INTO $tableName ($columnNamesSeparated) SELECT $columnNamesSeparated FROM $newTempTableName;")
database.execSQL("DROP TABLE ${newTempTableName};")
database.setTransactionSuccessful()
} finally {
database.endTransaction()
}
}
@JvmStatic
fun isTableExists(database: SQLiteDatabase, tableName: String): Boolean {
database.rawQuery(
"select DISTINCT tbl_name from sqlite_master where tbl_name = '$tableName'", null)
?.use {
return it.count > 0
} ?: return false
}
}
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();
}
}
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