SQL Database Cursors Tutorial200

Introduction

A SQL cursor is a temporary work area that stores a set of data from a database table. It allows you to iterate through the data row by row, making it a valuable tool for processing and manipulating database records.

Creating a Cursor

To create a cursor, use the following syntax:```sql
DECLARE cursor_name CURSOR FOR SELECT_statement;
```
where:
* `cursor_name` is the name of the cursor
* `SELECT_statement` is the SQL statement that defines the data to be fetched by the cursor

Opening a Cursor

Once a cursor is created, it needs to be opened before it can be used. To open a cursor, use the following statement:```sql
OPEN cursor_name;
```

Fetching Data from a Cursor

To fetch data from a cursor, use the `FETCH` statement. The syntax is as follows:```sql
FETCH cursor_name INTO variable_list;
```
where:
* `variable_list` is a list of variables to which the fetched data will be assigned

Updating Data in a Cursor

Cursors also allow you to update data in a table. To update data, use the `UPDATE` statement. The syntax is as follows:```sql
UPDATE table_name
SET column_name = new_value
WHERE CURRENT OF cursor_name;
```

Deleting Data from a Cursor

To delete data from a cursor, use the `DELETE` statement. The syntax is as follows:```sql
DELETE FROM table_name
WHERE CURRENT OF cursor_name;
```

Closing a Cursor

When you are finished with a cursor, you should close it to free up resources. To close a cursor, use the following statement:```sql
CLOSE cursor_name;
```

Cursor Types

There are three main types of cursors in SQL:* Static cursors: These cursors are read-only and provide a snapshot of the data at the time the cursor is opened. Any changes made to the underlying table after the cursor is opened will not be reflected in the cursor.
* Dynamic cursors: These cursors are read-write and reflect any changes made to the underlying table while the cursor is open.
* Keyset cursors: These cursors are used to fetch data from a table that has a unique index. They provide a more efficient way of fetching data compared to static or dynamic cursors.

When to Use Cursors

Cursors are useful in situations where you need to process data row by row, such as:* Iterating through a large dataset and performing some operation on each row
* Updating or deleting specific rows in a table
* Inserting new rows into a table

Conclusion

SQL cursors are a powerful tool for working with data in a database. They allow you to fetch, update, and delete data row by row, making them a valuable asset for a wide range of data processing tasks.

2025-01-11

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