Add support for mysql optimizer hint comments (#270)

Author: austintaylor

select.go

@@ -33,7 +33,8 @@ type SelectStmt struct {
 
 	comments Comments
 
-	indexHints []Builder
+	indexHints     []Builder
+	optimizerHints []Builder
 }
 
 type SelectBuilder = SelectStmt
@@ -54,6 +55,17 @@ func (b *SelectStmt) Build(d Dialect, buf Buffer) error {
 
 	buf.WriteString("SELECT ")
 
+	if len(b.optimizerHints) > 0 {
+		buf.WriteString("/*+ ")
+		for i, hint := range b.optimizerHints {
+			if i > 0 {
+				buf.WriteString(" ")
+			}
+			hint.Build(d, buf)
+		}
+		buf.WriteString(" */ ")
+	}
+
 	if b.IsDistinct {
 		buf.WriteString("DISTINCT ")
 	}
@@ -474,3 +486,16 @@ func (b *SelectStmt) IndexHint(hints ...interface{}) *SelectStmt {
 	}
 	return b
 }
+
+// OptimizerHint adds a MySQL optimizer hint. Hint can be a Builder or string.
+func (b *SelectStmt) OptimizerHint(hints ...interface{}) *SelectStmt {
+	for _, hint := range hints {
+		switch hint := hint.(type) {
+		case string:
+			b.optimizerHints = append(b.optimizerHints, Expr(hint))
+		case Builder:
+			b.optimizerHints = append(b.optimizerHints, hint)
+		}
+	}
+	return b
+}

select_test.go

@@ -24,11 +24,13 @@ func TestSelectStmt(t *testing.T) {
 		Suffix("FOR UPDATE").
 		Comment("SELECT TEST").
 		IndexHint(UseIndex("idx_c_d").ForGroupBy(), "USE INDEX(idx_e_f)").
-		IndexHint(IgnoreIndex("idx_a_b"))
+		IndexHint(IgnoreIndex("idx_a_b")).
+		OptimizerHint("NO_RANGE_OPTIMIZATION(table)").
+		OptimizerHint("MAX_EXECUTION_TIME(1000)")
 
 	err := builder.Build(dialect.MySQL, buf)
 	require.NoError(t, err)
-	require.Equal(t, "/* SELECT TEST */\nSELECT DISTINCT a, b FROM ? USE INDEX FOR GROUP BY(`idx_c_d`) USE INDEX(idx_e_f) IGNORE INDEX(`idx_a_b`) "+
+	require.Equal(t, "/* SELECT TEST */\nSELECT /*+ NO_RANGE_OPTIMIZATION(table) MAX_EXECUTION_TIME(1000) */ DISTINCT a, b FROM ? USE INDEX FOR GROUP BY(`idx_c_d`) USE INDEX(idx_e_f) IGNORE INDEX(`idx_a_b`) "+
 		"LEFT JOIN `table2` USE INDEX(`idx_table2`) ON table.a1 = table.a2 WHERE (`c` = ?) GROUP BY d HAVING (`e` = ?) ORDER BY f ASC LIMIT 3 OFFSET 4 FOR UPDATE", buf.String())
 	// two functions cannot be compared
 	require.Equal(t, 3, len(buf.Value()))