storage/sql: rework of the original MySQL PR

storage/sql/sql.go

@@ -91,20 +91,16 @@ var (
 			{matchLiteral("bytea"), "blob"},
 			{matchLiteral("timestamptz"), "datetime(3)"},
 			// MySQL doesn't support indicies on text fields w/o
-			// specifying key length. Use varchar instead (768 is
-			// the max key length for InnoDB with 4k pages).
-			{matchLiteral("text"), "varchar(768)"},
+			// specifying key length. Use varchar instead (767 byte
+			// is the max key length for InnoDB with 4k pages).
+			// For compound indexes (with two keys) even less.
+			{matchLiteral("text"), "varchar(384)"},
 			// Quote keywords and reserved words used as identifiers.
 			{regexp.MustCompile(`\b(keys)\b`), "`$1`"},
 			// Change default timestamp to fit datetime.
 			{regexp.MustCompile(`0001-01-01 00:00:00 UTC`), "1000-01-01 00:00:00"},
 		},
 	}
-
-	// Not tested.
-	flavorCockroach = flavor{
-		executeTx: crdb.ExecuteTx,
-	}
 )
 
 func (f flavor) translate(query string) string {