*: Check float length in parser

parser/parser.y

@@ -3681,6 +3681,16 @@ NumericType:
 		fopt := $2.(*coldef.FloatOpt)
 		x := types.NewFieldType($1.(byte))
 		x.Flen = fopt.Flen 
+		if x.Tp == mysql.TypeFloat {
+			// Fix issue #312
+			if x.Flen > 53 {
+				yylex.(*lexer).errf("Float len(%d) should not be greater than 53", x.Flen)
+				return 1
+			}
+			if x.Flen > 24 { 
+				x.Tp = mysql.TypeDouble
+			}
+		}
 		x.Decimal =fopt.Decimal
 		for _, o := range $3.([]*field.Opt) {
 			if o.IsUnsigned {

parser/parser_test.go

@@ -533,6 +533,10 @@ func (s *testParserSuite) TestParser0(c *C) {
 		{`select * from t as a`, true},
 		{"select 1 full, 1 row, 1 abs", true},
 		{"select * from t full, t1 row, t2 abs", true},
+
+		// For https://github.com/pingcap/tidb/issues/312
+		{`create table t (c float(53));`, true},
+		{`create table t (c float(54));`, false},
 	}
 
 	for _, t := range table {

stmt/stmts/create_test.go

@@ -103,6 +103,44 @@ func (s *testStmtSuite) TestCreateTable(c *C) {
 
 	// Test "if not exist"
 	mustExec(c, s.testDB, "CREATE TABLE if not exists test(id INT NOT NULL DEFAULT 1, name varchar(255), PRIMARY KEY(id));")
+
+	// Testcase for https://github.com/pingcap/tidb/issues/312
+	mustExec(c, s.testDB, `create table issue312_1 (c float(24));`)
+	mustExec(c, s.testDB, `create table issue312_2 (c float(25));`)
+	tx = mustBegin(c, s.testDB)
+	rows, err := tx.Query(`desc issue312_1`)
+	c.Assert(err, IsNil)
+	for rows.Next() {
+		var (
+			c1 string
+			c2 string
+			c3 string
+			c4 string
+			c5 string
+			c6 string
+		)
+		rows.Scan(&c1, &c2, &c3, &c4, &c5, &c6)
+		c.Assert(c2, Equals, "float")
+	}
+	rows.Close()
+	mustCommit(c, tx)
+	tx = mustBegin(c, s.testDB)
+	rows, err = tx.Query(`desc issue312_2`)
+	c.Assert(err, IsNil)
+	for rows.Next() {
+		var (
+			c1 string
+			c2 string
+			c3 string
+			c4 string
+			c5 string
+			c6 string
+		)
+		rows.Scan(&c1, &c2, &c3, &c4, &c5, &c6)
+		c.Assert(c2, Equals, "double")
+	}
+	rows.Close()
+	mustCommit(c, tx)
 }
 
 func (s *testStmtSuite) TestCreateIndex(c *C) {