## Vert.x Common SQL interface

The common SQL interface is used to interact with Vert.x SQL services.

You obtain a connection to the database via the service interface for the specific SQL service that you are using (e.g. JDBC/MySQL/PostgreSQL).

## The SQL Connection

A connection to the database is represented by `SQLConnection`.

### Auto-commit

When you obtain a connection auto commit is set to `true`. This means that each operation you perform will effectively execute in its own transaction.

If you wish to perform multiple operations in a single transaction you should set auto commit to false with `setAutoCommit`.

When the operation is complete, the handler will be called:

    connection.set_auto_commit(false) { |res_err,res|
      if (res_err == nil)
        # OK!
      else
        # Failed!
      end
    }

### Executing queries

To execute a query use `query`

The query string is raw SQL that is passed through without changes to the actual database.

The handler will be called with the results, represented by `ResultSet` when the query has been run.

    connection.query("SELECT ID, FNAME, LNAME, SHOE_SIZE from PEOPLE") { |res_err,res|
      if (res_err == nil)
        # Get the result set
        resultSet = res
      else
        # Failed!
      end
    }

The `ResultSet` instance represents the results of a query.

The list of column names are available with `getColumnNames`, and the actual results available with `getResults`

The results are a list of `JsonArray` instances, one for each row of the results.

    columnNames = resultSet['columnNames']

    results = resultSet['results']

    results.each do |row|

      id = row[0]
      fName = row[1]
      lName = row[2]
      shoeSize = row[3]

    end

You can also retrieve the rows as a list of Json object instances with `getRows` - this can give you a somewhat simpler API to work with, but please be aware that SQL results can contain duplicate column names - if that’s the case you should use `getResults` instead.

Here’s an example of iterating through the results as Json object instances:

    rows = resultSet['rows']

    rows.each do |row|

      id = row['ID']
      fName = row['FNAME']
      lName = row['LNAME']
      shoeSize = row['SHOE_SIZE']

    end

### Prepared statement queries

To execute a prepared statement query you can use `queryWithParams`.

This takes the query, containing the parameter place holders, and a `JsonArray` or parameter values.

    query = "SELECT ID, FNAME, LNAME, SHOE_SIZE from PEOPLE WHERE LNAME=? AND SHOE_SIZE > ?"
    params = [
      "Fox",
      9
    ]

    connection.query_with_params(query, params) { |res_err,res|

      if (res_err == nil)
        # Get the result set
        resultSet = res
      else
        # Failed!
      end
    }

### Executing INSERT, UPDATE or DELETE

To execute an operation which updates the database use `update`.

The update string is raw SQL that is passed through without changes to the actual database.

The handler will be called with the results, represented by `UpdateResult` when the update has been run.

The update result holds the number of rows updated with `getUpdated`, and if the update generated keys, they are available with `getKeys`.

    columnNames = resultSet['columnNames']

    results = resultSet['results']

    results.each do |row|

      id = row[0]
      fName = row[1]
      lName = row[2]
      shoeSize = row[3]

    end

### Prepared statement updates

To execute a prepared statement update you can use `updateWithParams`.

This takes the update, containing the parameter place holders, and a `JsonArray` or parameter values.

    update = "UPDATE PEOPLE SET SHOE_SIZE = 10 WHERE LNAME=?"
    params = [
      "Fox"
    ]

    connection.update_with_params(update, params) { |res_err,res|

      if (res_err == nil)

        updateResult = res

        puts "No. of rows updated: #{updateResult['updated']}"

      else

        # Failed!

      end
    }

### Executing other operations

To execute any other database operation, e.g. a `CREATE TABLE` you can use `execute`.

The string is passed through without changes to the actual database. The handler is called when the operation is complete

    sql = "CREATE TABLE PEOPLE (ID int generated by default as identity (start with 1 increment by 1) not null,FNAME varchar(255), LNAME varchar(255), SHOE_SIZE int);"

    connection.execute(sql) { |execute_err,execute|
      if (execute_err == nil)
        puts "Table created !"
      else
        # Failed!
      end
    }

### Using transactions

To use transactions first set auto-commit to false with `setAutoCommit`.

You then do your transactional operations and when you want to commit or rollback use `commit` or `rollback`.

Once the commit/rollback is complete the handler will be called and the next transaction will be automatically started.

    # Do stuff with connection - updates etc

    # Now commit

    connection.commit() { |res_err,res|
      if (res_err == nil)
        # Committed OK!
      else
        # Failed!
      end
    }

### Closing connections

When you’ve done with the connection you should return it to the pool with `close`.