error for enum truncation

Author: max-hoffman

enginetest/queries/script_queries.go

@@ -130,9 +130,10 @@ var ScriptTests = []ScriptTest{
 			{
 				Query: "alter table xy modify y enum('a','b','c')",
 			},
-			//{
-			//	Query: "alter table xy modify y enum('a')",
-			//},
+			{
+				Query:       "alter table xy modify y enum('a')",
+				ExpectedErr: sql.ErrEnumTypeTruncated,
+			},
 		},
 	},
 	{

sql/analyzer/validate_create_table.go

@@ -470,6 +470,15 @@ func validateModifyColumn(ctx *sql.Context, initialSch sql.Schema, schema sql.Sc
 		return nil, err
 	}
 
+	if e1, ok := newCol.Type.(sql.EnumType); ok {
+		oldCol := initialSch[initialSch.IndexOfColName(oldColName)]
+		if e2, ok := oldCol.Type.(sql.EnumType); ok {
+			if len(e1.Values()) < len(e2.Values()) {
+				return nil, sql.ErrEnumTypeTruncated.New()
+			}
+		}
+	}
+
 	// TODO: When a column is being modified, we should ideally check that any existing table check constraints
 	//       are still valid (e.g. if the column type changed) and throw an error if they are invalidated.
 	//       That would be consistent with MySQL behavior.

sql/errors.go

@@ -924,6 +924,8 @@ var (
 	ErrInvalidTypeForLimit = errors.NewKind("invalid limit. expected %T, found %T")
 
 	ErrColumnSpecifiedTwice = errors.NewKind("column '%v' specified twice")
+
+	ErrEnumTypeTruncated = errors.NewKind("new enum type change truncates value")
 )
 
 // CastSQLError returns a *mysql.SQLError with the error code and in some cases, also a SQL state, populated for the