Drop column Room migration android - android-studio

Question

I have a table Server
#Entity(tableName = "servers")
data class ServerDto(
#PrimaryKey
#ColumnInfo(name = "server_id")
var serverId: Long,
#ColumnInfo(name = "address", defaultValue = "")
var serverAddress: String,
#ColumnInfo(name = "description", defaultValue = "")
var serverDescription: String,
#ColumnInfo(name = "file_segment")
var fileSegment: Int
) : Serializable
and a table accounts
#Entity(tableName = "accounts", primaryKeys = ["server_id", "account_id"])
data class AccountDto(
#ColumnInfo(name = "server_id")
val serverId: Long,
#ColumnInfo(name = "account_id")
val accountId: Int,
#ColumnInfo(name = "username", defaultValue = "")
val username: String,
#ColumnInfo(name = "password", defaultValue = "")
val password: String,
#ColumnInfo(name = "first_name", defaultValue = "")
var firstname: String,
#ColumnInfo(name = "last_name", defaultValue = "")
var lastname: String,
#ColumnInfo(name = "email", defaultValue = "")
var email: String,
#ColumnInfo(name = "active")
var active: Int
) : Serializable
I want to transfer 2 columns (username, password) from accounts to server and then remove them from accounts. I wrote the Migrations but i see that Android Studio does not allow to write DROP COLUMN since it underlines it with red. What is wrong with that??
override fun migrate(database: SupportSQLiteDatabase) {
database.execSQL("ALTER TABLE servers ADD COLUMN username VARCHAR")
database.execSQL("ALTER TABLE servers ADD COLUMN password VARCHAR")
database.execSQL("UPDATE servers SET username = (SELECT a.username FROM accounts a where a.server_id = servers.server_id and a.active = 1)")
database.execSQL("UPDATE servers SET password = (SELECT a.password FROM accounts a where a.server_id = servers.server_id and a.active = 1)")
database.execSQL("ALTER TABLE accounts ***DROP*** COLUMN username")
database.execSQL("ALTER TABLE accounts ***DROP*** COLUMN password")
}

Answer 1

SQLite doesn't support column deletion straight away.
You will have to do migration steps as follows:
Source: https://www.sqlite.org/faq.html#q11
CREATE TABLE accounts_backup(serverId VARCHAR, accountId VARCHAR, firstname VARCHAR, lastname VARCHAR, email VARCHAR, active VARCHAR);
INSERT INTO accounts_backup SELECT serverId, accountId, firstname, lastname, email, active FROM accounts;
DROP TABLE accounts;
CREATE TABLE accounts(serverId VARCHAR, accountId VARCHAR, firstname VARCHAR, lastname VARCHAR, email VARCHAR, active VARCHAR);
INSERT INTO accounts SELECT serverId, accountId, firstname, lastname, email, active FROM accounts_backup;
DROP TABLE accounts_backup;

Answer 2

Here's a combination of the previous two answers, written in Kotlin for Android:
private val MIGRATION_3_2 = object : Migration(3,2) {
override fun migrate(database: SupportSQLiteDatabase) {
//Drop column isn't supported by SQLite, so the data must manually be moved
with(database) {
execSQL("CREATE TABLE Users_Backup (id INTEGER, name TEXT, PRIMARY KEY (id))")
execSQL("INSERT INTO Users_Backup SELECT id, name FROM Users")
execSQL("DROP TABLE Users")
execSQL("ALTER TABLE Users_Backup RENAME to Users")
}
}
}