*: added builtin function sqrt (pingcap#2493)

ast/functions.go

@@ -85,6 +85,7 @@ const (
 	Rand    = "rand"
 	Round   = "round"
 	Sign    = "sign"
+	Sqrt    = "sqrt"
 
 	// time functions
 	Curdate          = "curdate"

expression/builtin.go

@@ -157,6 +157,7 @@ var Funcs = map[string]Func{
 	ast.Rand:    {builtinRand, 0, 1},
 	ast.Round:   {builtinRound, 1, 2},
 	ast.Sign:    {builtinSign, 1, 1},
+	ast.Sqrt:    {builtinSqrt, 1, 1},
 	ast.Conv:    {builtinConv, 3, 3},
 	ast.CRC32:   {builtinCRC32, 1, 1},
 

expression/builtin_math.go

@@ -42,6 +42,7 @@ var (
 	_ functionClass = &convFunctionClass{}
 	_ functionClass = &crc32FunctionClass{}
 	_ functionClass = &signFunctionClass{}
+	_ functionClass = &sqrtFunctionClass{}
 	_ functionClass = &arithmeticFunctionClass{}
 )
 
@@ -57,6 +58,7 @@ var (
 	_ builtinFunc = &builtinConvSig{}
 	_ builtinFunc = &builtinCRC32Sig{}
 	_ builtinFunc = &builtinSignSig{}
+	_ builtinFunc = &builtinSqrtSig{}
 	_ builtinFunc = &builtinArithmeticSig{}
 )
 
@@ -552,6 +554,49 @@ func builtinSign(args []types.Datum, ctx context.Context) (d types.Datum, err er
 	return d, nil
 }
 
+type sqrtFunctionClass struct {
+	baseFunctionClass
+}
+
+func (c *sqrtFunctionClass) getFunction(args []Expression, ctx context.Context) (builtinFunc, error) {
+	return &builtinSignSig{newBaseBuiltinFunc(args, ctx)}, errors.Trace(c.verifyArgs(args))
+}
+
+type builtinSqrtSig struct {
+	baseBuiltinFunc
+}
+
+func (b *builtinSqrtSig) eval(row []types.Datum) (types.Datum, error) {
+	args, err := b.evalArgs(row)
+	if err != nil {
+		return types.Datum{}, errors.Trace(err)
+	}
+	return builtinSqrt(args, b.ctx)
+}
+
+// See http://dev.mysql.com/doc/refman/5.7/en/mathematical-functions.html#function_sqrt
+func builtinSqrt(args []types.Datum, ctx context.Context) (d types.Datum, err error) {
+	if args[0].IsNull() {
+		return args[0], nil
+	}
+
+	sc := ctx.GetSessionVars().StmtCtx
+	f, err := args[0].ToFloat64(sc)
+	if err != nil {
+		return d, errors.Trace(err)
+	}
+
+	// negative value does not have any square root in rational number
+	// Need return null directly.
+	if f < 0 {
+		d.SetNull()
+		return d, nil
+	}
+
+	d.SetFloat64(math.Sqrt(f))
+	return
+}
+
 type arithmeticFunctionClass struct {
 	baseFunctionClass
 

expression/builtin_math_test.go

@@ -292,3 +292,26 @@ func (s *testEvaluatorSuite) TestSign(c *C) {
 		c.Assert(v, testutil.DatumEquals, types.NewDatum(t.ret))
 	}
 }
+
+func (s *testEvaluatorSuite) TestSqrt(c *C) {
+	defer testleak.AfterTest(c)()
+	tbl := []struct {
+		Arg interface{}
+		Ret interface{}
+	}{
+		{nil, nil},
+		{int64(1), float64(1)},
+		{float64(4), float64(2)},
+		{"4", float64(2)},
+		{"9", float64(3)},
+		{"-16", nil},
+	}
+
+	Dtbl := tblToDtbl(tbl)
+
+	for _, t := range Dtbl {
+		v, err := builtinSqrt(t["Arg"], s.ctx)
+		c.Assert(err, IsNil)
+		c.Assert(v, DeepEquals, t["Ret"][0], Commentf("arg:%v", t["Arg"]))
+	}
+}

parser/misc.go

@@ -376,6 +376,7 @@ var tokenMap = map[string]int{
 	"SNAPSHOT":            snapshot,
 	"SOME":                some,
 	"SPACE":               space,
+	"SQRT":                sqrt,
 	"START":               start,
 	"STARTING":            starting,
 	"STATS_PERSISTENT":    statsPersistent,

parser/parser.y

@@ -272,6 +272,7 @@ import (
 	second		"SECOND"
 	sign		"SIGN"
 	sleep		"SLEEP"
+	sqrt 		"SQRT"
 	calcFoundRows	"SQL_CALC_FOUND_ROWS"
 	strcmp		"STRCMP"
 	strToDate	"STR_TO_DATE"
@@ -2145,7 +2146,7 @@ NotKeywordToken:
 |	"DATEDIFF" | "DATE_ADD" | "DATE_FORMAT" | "DATE_SUB" | "DAYNAME" | "DAYOFMONTH" | "DAYOFWEEK" | "DAYOFYEAR" | "FROM_DAYS" | "FIND_IN_SET" | "FOUND_ROWS"
 |	"GROUP_CONCAT"| "GREATEST" | "LEAST" | "HOUR" | "HEX" | "UNHEX" | "IFNULL" | "ISNULL" | "LAST_INSERT_ID" | "LCASE" | "LENGTH" | "LOCATE" | "LOWER" | "LTRIM"
 |	"MAX" | "MICROSECOND" | "MIN" |	"MINUTE" | "NULLIF" | "MONTH" | "MONTHNAME" | "NOW" | "POW" | "POWER" | "RAND"
-|	"SECOND" | "SIGN" | "SLEEP" | "SQL_CALC_FOUND_ROWS" | "STR_TO_DATE" | "SUBDATE" | "SUBSTRING" %prec lowerThanLeftParen |
+|	"SECOND" | "SIGN" | "SLEEP" | "SQRT" | "SQL_CALC_FOUND_ROWS" | "STR_TO_DATE" | "SUBDATE" | "SUBSTRING" %prec lowerThanLeftParen |
 "SUBSTRING_INDEX" | "SUM" | "TRIM" | "RTRIM" | "UCASE" | "UPPER" | "VERSION" | "WEEKDAY" | "WEEKOFYEAR" | "YEARWEEK" | "ROUND"
 |	"STATS_PERSISTENT" | "GET_LOCK" | "RELEASE_LOCK" | "CEIL" | "CEILING" | "FROM_UNIXTIME" | "TIMEDIFF" | "LN" | "LOG" | "LOG2" | "LOG10" | "FIELD_KWD"
 
@@ -2929,6 +2930,11 @@ FunctionCallNonKeyword:
 	{
 		$$ = &ast.FuncCallExpr{FnName: model.NewCIStr($1), Args: []ast.ExprNode{$3.(ast.ExprNode)}}
 	}
+|	"SQRT" '(' Expression ')'
+	{
+		$$ = &ast.FuncCallExpr{FnName: model.NewCIStr($1), Args: []ast.ExprNode{$3.(ast.ExprNode)}}
+	}
+
 |	"SLEEP" '(' Expression ')'
 	{
 		$$ = &ast.FuncCallExpr{FnName: model.NewCIStr($1), Args: []ast.ExprNode{$3.(ast.ExprNode)}}

parser/parser_test.go

@@ -523,6 +523,7 @@ func (s *testParserSuite) TestBuiltin(c *C) {
 		{"SELECT CONV(10+'10'+'10'+X'0a',10,10);", true},
 		{"SELECT CRC32('MySQL');", true},
 		{"SELECT SIGN(0);", true},
+		{"SELECT SQRT(0);", true},
 
 		{"SELECT SUBSTR('Quadratically',5);", true},
 		{"SELECT SUBSTR('Quadratically',5, 3);", true},

plan/typeinferer.go

@@ -283,7 +283,7 @@ func (v *typeInferrer) handleFuncCallExpr(x *ast.FuncCallExpr) {
 		} else {
 			tp = types.NewFieldType(mysql.TypeLonglong)
 		}
-	case "ln", "log", "log2", "log10":
+	case "ln", "log", "log2", "log10", "sqrt":
 		tp = types.NewFieldType(mysql.TypeDouble)
 	case "pow", "power", "rand":
 		tp = types.NewFieldType(mysql.TypeDouble)

plan/typeinferer_test.go

@@ -94,6 +94,7 @@ func (ts *testTypeInferrerSuite) TestInferType(c *C) {
 		{"LOG(3, 10)", mysql.TypeDouble, charset.CharsetBin},
 		{"LOG2(3)", mysql.TypeDouble, charset.CharsetBin},
 		{"LOG10(3)", mysql.TypeDouble, charset.CharsetBin},
+		{"SQRT(3)", mysql.TypeDouble, charset.CharsetBin},
 		{"rand()", mysql.TypeDouble, charset.CharsetBin},
 		{"curdate()", mysql.TypeDate, charset.CharsetBin},
 		{"current_date()", mysql.TypeDate, charset.CharsetBin},