drop-table | 易学教程

DROP IF EXISTS VS DROP?

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问题 Can someone tell me if there is any difference between DROP IF EXISTS [TABLE_NAME] DROP [TABLE_NAME] I am asking this because I am using JDBC template in my MVC web application. If I use DROP [TABLE_NAME] the error said that Table exist. And if I use DROP IF EXISTS [TABLE_NAME] it says bad SQL grammar. Can some one help? 回答1: Standard SQL syntax is DROP TABLE table_name; IF EXISTS is not standard; different platforms might support it with different syntax, or not support it at all. In

How to delete a table in SQLAlchemy?

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问题 I want to delete a table using SQLAlchemy. Since I am testing over and over again, I want to delete the table my_users so that I can start from scratch every single time. So far I am using SQLAlchemy to execute raw SQL through the engine.execute() method: sql = text('DROP TABLE IF EXISTS my_users;') result = engine.execute(sql) However, I wonder if there is some standard way to do so. The only one I could find is drop_all(), but it deletes all the structure, not only one specific table: Base

Android SQLite Database, WHY drop table and recreate on upgrade

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In the tutorials I am following and a lot of more places I see this, onUpgrade -> drop table if exists, then recreate table. What is the purpose of this? private static class DbHelper extends SQLiteOpenHelper{ public DbHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL("CREATE TABLE " + DATABASE_TABLE + " (" + KEY_ROWID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_NAME + " TEXT NOT NULL, " + KEY_HOTNESS + " TEXT NOT NULL);" ); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int

Android SQLite Database, WHY drop table and recreate on upgrade

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问题 In the tutorials I am following and a lot of more places I see this, onUpgrade -> drop table if exists, then recreate table. What is the purpose of this? private static class DbHelper extends SQLiteOpenHelper{ public DbHelper(Context context) { super(context, DATABASE_NAME, null, DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { db.execSQL(\"CREATE TABLE \" + DATABASE_TABLE + \" (\" + KEY_ROWID + \" INTEGER PRIMARY KEY AUTOINCREMENT, \" + KEY_NAME + \" TEXT NOT NULL, \"