ANDROID STUDIO / SQLiteLog：（1）在“LIMIT”附近：语法错误

Question

I am trying to delete the duplicates that I am getting in my database using DELETE function of my SQL with LIMIT 1 but it is showing me the "LIMIT" syntax error.

        myDatabase.execSQL("CREATE TABLE IF NOT EXISTS users (name VARCHAR , age INT(3))");

        myDatabase.execSQL("INSERT INTO users (name, age) VALUES ('Vaishant', 21)");

        myDatabase.execSQL("INSERT INTO users (name, age) VALUES ('Tommy',4)");

        myDatabase.execSQL("DELETE FROM users WHERE name = 'Vaishant' LIMIT 1");

Can someone tell me why I am getting this error and how to correct it?

Answer 1

SQLite does not support LIMIT in a DELETE statement.
Use a subquery that returns the rowid of a row that contains the name that you search for:

String sql = "DELETE FROM users WHERE rowid = (SELECT rowid FROM users WHERE name = 'Vaishant' LIMIT 1)";
myDatabase.execSQL(sql);

If you want to delete the duplicate names and keep only 1, then you can do this:

DELETE FROM users
WHERE NOT EXISTS (SELECT 1 FROM users u WHERE u.name = users.name AND u.rowid < users.rowid)

or:

DELETE FROM users
WHERE rowid NOT IN (SELECT MIN(rowid) FROM users GROUP BY name)

Answer 2

In your delete statement you are using limit with Delete query. You should use it as below:

1. First add id column as primary key in your table

   myDatabase.execSQL("CREATE TABLE IF NOT EXISTS users (ID INTEGER PRIMARY KEY AUTOINCREMENT, name VARCHAR, age INT(3))");

2. change the query of delete as below

   myDatabase.execSQL("DELETE FROM users WHERE id IN (SELECT id FROM (SELECT id, ROW_NUMBER() OVER (PARTITION BY name ORDER BY name) AS row_num FROM users )t WHERE row_num > 1)");