SQL Expressions: Re-implement feature using go-mysql-server (#99521)

* Under feature flag `sqlExpressions` and is experimental
* Excluded from arm32
* Will not work with the Query Service yet
* Does not have limits in place yet
* Does not working with alerting yet
* Currently requires "prepare time series" Transform for time series viz
 
---------

Co-authored-by: Sam Jewell <sam.jewell@grafana.com>

pkg/expr/sql/db.go

@@ -1,22 +1,61 @@
+//go:build !arm
+
 package sql
 
 import (
-	"errors"
+	"context"
 
+	sqle "github.com/dolthub/go-mysql-server"
+	mysql "github.com/dolthub/go-mysql-server/sql"
+
+	"github.com/dolthub/go-mysql-server/sql/analyzer"
 	"github.com/grafana/grafana-plugin-sdk-go/data"
 )
 
-type DB struct {
-}
+// DB is a database that can execute SQL queries against a set of Frames.
+type DB struct{}
 
-func (db *DB) RunCommands(commands []string) (string, error) {
-	return "", errors.New("not implemented")
-}
+// QueryFrames runs the sql query query against a database created from frames, and returns the frame.
+// The RefID of each frame becomes a table in the database.
+// It is expected that there is only one frame per RefID.
+// The name becomes the name and RefID of the returned frame.
+func (db *DB) QueryFrames(ctx context.Context, name string, query string, frames []*data.Frame) (*data.Frame, error) {
+	// We are parsing twice due to TablesList, but don't care fow now. We can save the parsed query and reuse it later if we want.
+	if allow, err := AllowQuery(query); err != nil || !allow {
+		if err != nil {
+			return nil, err
+		}
+		return nil, err
+	}
 
-func (db *DB) QueryFramesInto(name string, query string, frames []*data.Frame, f *data.Frame) error {
-	return errors.New("not implemented")
-}
+	pro := NewFramesDBProvider(frames)
+	session := mysql.NewBaseSession()
+	mCtx := mysql.NewContext(ctx, mysql.WithSession(session))
 
-func NewInMemoryDB() *DB {
-	return &DB{}
+	// Select the database in the context
+	mCtx.SetCurrentDatabase(dbName)
+
+	// Empty dir does not disable secure_file_priv
+	//ctx.SetSessionVariable(ctx, "secure_file_priv", "")
+
+	// TODO: Check if it's wise to reuse the existing provider, rather than creating a new one
+	a := analyzer.NewDefault(pro)
+
+	engine := sqle.New(a, &sqle.Config{
+		IsReadOnly: true,
+	})
+
+	schema, iter, _, err := engine.Query(mCtx, query)
+	if err != nil {
+		return nil, err
+	}
+
+	f, err := convertToDataFrame(mCtx, iter, schema)
+	if err != nil {
+		return nil, err
+	}
+	f.Name = name
+	f.RefID = name
+
+	return f, nil
 }