allow truncated strings when cast as date

Author: angelamayxie

enginetest/queries/queries.go

@@ -4285,6 +4285,12 @@ SELECT * FROM cte WHERE  d = 2;`,
 		Query:    "select cast('2020-01-01 12:34:56.123456' as datetime(6)) > cast('2020-01-01 12:34:56' as datetime)",
 		Expected: []sql.Row{{true}},
 	},
+	{
+		Query:                 "select cast('2020-01-01 a' as date)",
+		ExpectedWarning:       1292,
+		ExpectedWarningsCount: 1,
+		Expected:              []sql.Row{{time.Date(2020, time.January, 1, 0, 0, 0, 0, time.UTC)}},
+	},
 	{
 		Query: `SELECT * FROM (SELECT * FROM (SELECT * FROM (SELECT * FROM othertable) othertable_one) othertable_two) othertable_three WHERE s2 = 'first'`,
 		Expected: []sql.Row{

sql/expression/convert.go

@@ -331,7 +331,10 @@ func convertValue(ctx *sql.Context, val interface{}, castTo string, originType s
 		}
 		d, _, err := types.Date.Convert(ctx, val)
 		if err != nil {
-			return nil, err
+			if !sql.ErrTruncatedIncorrect.Is(err) {
+				return nil, err
+			}
+			ctx.Warn(mysql.ERTruncatedWrongValue, "%s", err.Error())
 		}
 		return d, nil
 	case ConvertToDatetime: