Introduce Stmt.ExplainQueryPlan.

trace.go

@@ -27,6 +27,7 @@ import "C"
 
 import (
 	"fmt"
+	"io"
 	"time"
 	"unsafe"
 )
@@ -431,3 +432,28 @@ func ConfigUri(b bool) error {
 	}
 	return Errno(rv)
 }
+
+func (s *Stmt) ExplainQueryPlan(w io.Writer) error {
+	sql := s.SQL()
+	if len(sql) == 0 {
+		return s.specificError("empty statement")
+	}
+	explain := Mprintf("EXPLAIN QUERY PLAN %s", s.SQL())
+
+	sExplain, err := s.Conn().prepare(explain)
+	if err != nil {
+		return err
+	}
+	defer sExplain.finalize()
+
+	var selectid, order, from int
+	var detail string
+	err = sExplain.Select(func(s *Stmt) error {
+		if err := s.Scan(&selectid, &order, &from, &detail); err != nil {
+			return err
+		}
+		fmt.Fprintf(w, "%d\t%d\t%d\t%s\n", selectid, order, from, detail)
+		return nil
+	})
+	return err
+}

trace_test.go

@@ -6,6 +6,7 @@ package sqlite_test
 
 import (
 	"fmt"
+	"os"
 	"testing"
 	"time"
 
@@ -119,7 +120,7 @@ func TestTrace(t *testing.T) {
 	defer checkClose(db, t)
 	db.Trace(trace, t)
 	err := db.SetAuthorizer(authorizer, t)
-	checkNoError(t, err, "couldn't set an authorizer")
+	checkNoError(t, err, "couldn't set an authorizer: %s")
 	db.Profile(profile, t)
 	db.ProgressHandler(progressHandler, 1, t)
 	db.CommitHook(commitHook, t)
@@ -140,3 +141,16 @@ func TestMemory(t *testing.T) {
 	limit := SoftHeapLimit()
 	assert.T(t, limit >= 0, "soft heap limit positive")
 }
+
+func TestExplainQueryPlan(t *testing.T) {
+	db := open(t)
+	defer checkClose(db, t)
+	createTable(db, t)
+	s, err := db.Prepare("SELECT * FROM test WHERE a_string like ?")
+	checkNoError(t, err, "error while preparing stmt: %s")
+	defer checkFinalize(s, t)
+	w, err := os.Open(os.DevNull)
+	checkNoError(t, err, "couldn't open /dev/null: %s")
+	err = s.ExplainQueryPlan(w)
+	checkNoError(t, err, "error while explaining query plan: %s")
+}